2011 10 Physics Power Point New

8/2/2019 2011 10 Physics Power Point New

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CURRENTELECTRICITY


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Electrical Appliances in theHome

All electrical appliances _________ electrical _________ intoanother, more _________ form of energy.

Electrical energy (__________) is produced because it is_______ to __________, __________, __________, and

__________.

Appliance Energy Conversions

convert

energyuseful

electricity easyproduce transport control conver

t

Radiant Heater MainPurpose:

Electricalenergy

-> Heat Energy

Waste:Electrical

energy

-> Light Energy (glowing)-> Sound Energy

(humming)Fan Heater MainPurpose:

Electricalenergy

-> Heat Energy-> Kinetic Energy

Waste:Electricalenergy

-> Sound Energy(humming)

Light Bulb Main

Purpose:

Electrical

energy

-> light Energy

Waste:Electrical -> Heat Energy


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Efficiency of Appliances

All electrical appliances or ___________ have an

______________ Efficiency is the __________ (or ______________) of the

energy that is _________ the that device is used for the ____we _____________

Efficiency = Energy Used to do

To make this a percentage; multiply it by 100 Energy __________ = _____________ Energy Used to do

__________

Example: In a light bulb, 100J of energy is input and 70J of heat isroduced. What is the efficienc of the li ht bulb as a decimal and

device

s

efficiency

fraction percentageputinto

work want it to do

Main Job

Total EnergyIn

waste

d

Total Energy

In

Main Job

Energy for Main Job =100J 70J

= 30JTotal Ener In =100J

Efficiency = Main Job / Total In

= 30/100= 0.3 = 30%


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Efficiency of AppliancesQuestions

1. When heating water a kettle ran for 5 minutes using 50J of energy. Only 40J ofenergy was used to heat the water; the rest was wasted on heating the

surroundings and producing sound. How efficient is the kettle?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. A space heater claims to be 80% efficient. In a test it was found that 350J ofenergy was needed to run the heater, 200J of energy was used to produce heat,80J went into driving the fan, and 70J of sound energy was produced. Is the heater80% efficient? Why?

____________________________________________________________________________________________________________________________________

____________________________________________________________________________________________________________________________________________________________________

3. A computer is said to waste 15% of the electrical energy used on things likeproducing heat (and the cooling system to cool it) and sound. If a computer uses anaverage of 750J of energy a day, how much energy is wasted each day? Howenergy much is useful?

__________________________________________________________________


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Static and Current Electricity

There are two types of electricity: Static

Electricity:______________________________

CurrentElectricity:_____________________________

We will be dealing with Current Electricity

To get current to flow we need:

__________________________________________

_______________________________________

build up of electrical charge then suddenrelease

flow of electrical charge (electrons) along aconductor

A closed path (a complete circuit)A power supply to push the electrons (battery)

Conductors for the electrons to travel on (i.e. copperwires)A load - something for the electrical energy to be

transferred to (i.e. Light bulb, resistor, motor, etc.)


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Current (I) Current (I) is the ______________.

It is measured in __________________. 1 amp is _________ of electrons flowing past a given point in

1second

Amperes are measured with an _______________.

Typical current values: Small torch:____________

Car headlight:________

Electric kettle:________

flow of electrons

amperes (A)1 Coulomb

ammeter ACircuit diagramsymbol

0.2A = 200mA

4A

10A

This is 6.2 x 1018 electrons.Thats 62 followed by 17zeros!!!!

Direction electronsflow

Direction it isdrawn on adiagram (howscientists

used to thinkit went

PositiveTerminal (thelong one)

Negative Terminal(the short one)


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Current Homework 1. Read pages 40-42 in textbook2. Answer the Questions Below

1. What is electric current?____________________________________________________________________

______________________________________________________________________________________________________________________________________________________ _______

2. Explain the difference between real and conventional current.

____________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. What kind of current is generated from a battery? A solar cell? What do you get from powerpoint?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. What device is used to measure current (name and symbol)?________________________


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Generating Electricity There are many ways to generate electricity but they all involve

________________ other types of energy. There are 3 ways:

1. Batteries use ______________ to produce ___ current.

What we call batteries are really _____. When we place 2 or more

________ together we get a battery.

2. Solar Cells use ______________ to produce ____ current.

More and more, solar cells are being used in__________________ electricity production. Like with batteries

thousands of solar cells can be ________________________ toproduce huge amounts of electricity.

3. Magnets use _______________ to produce ____ current.

Magnets are passed through a ________________. When this

happens, a current is _____________. This process is called

transforming

chemical energy DC

DC = directcurrent

cells

cells

light energy DC

large scale

combined together in series

kinetic energy AC

coil of wireinduced

Electro Magnetic Induction

S


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Power Stations All Power Stations use electromagnetic induction to produce

energy. They simple use different ways to _______________.

The device with a ________ magnet inside a coil is called a__________. A ___________ is attached to it which turns themagnet.

As we saw from the simulation we can increase the output fromelectromagnetic induction by: 1.________________________2._______________________

3._________________________ 4._____________________________

This is all power stations do!!!

Hydro-Electric Stations: (Youtube: Hydro-Electric Power How it Works)

Use _________ Energy from ________ water to turn turbine____________.

Coal Stations: (Youtube: How a coal power station works)

Burns coal which releases __________________. This is usedto __________ water to produce _______ which turns the

turbine.

turn the magnet

rotating generatorturbine

Increase the Strength ofMagnet

Rotate magnet faster

Increase # of turns in coil Increase diameter of coil

kinetic moving directly

chemical potentialheat & boil steam

Neutrons Uranium nucleusnuclear energy heat &

boil steam


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Potential Difference (Voltage)

We can think of voltage in two ways: 1. As the _________ given to get electrons _______

Sometimes referred to as _____ (_____________________)

Used to describe an ____________ (i.e The voltage of a typical cell is_____; we can place cells together in ______ (to form a __________)

to increase the voltage. 2 1.5V cells in series gives ______, 6 1.5Vcells in series give _____.

2. The amount of ________________________ the electrons have

How much energy is available to be _____________ (i.e. Into_______ in a speaker or ________ in a toaster)

Each ________ (or _____) in a circuit uses up some of the electricpotential of the electrons; this is why we use the term _______________________ (describes the difference in the electric potentialenergy between _____________ in a circuit or the ____________)

All electrons in a circuit will also return to the power supply with____ of electric potential energy. It is all ________ in the circuit!

push flowingEMF electro motive force

energy source 1.5Vseries battery

3V 9VElectric Potential Energy

transformed

soundheat

device

loadpotential difference

any 2 points voltage drop

0Vusedup


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Measuring Voltage Voltage is measured in __________________.

1 volt means each coulomb of charge(______________ electrons)

is given 1 joule of electrical energy. Voltage are measured with a ___________________.

A typical cell provides a V or EMF of ______.

Connecting two or more in ______ to form a _______ increases

voltage.

volts (V)

6.2 x 1018

voltmeter

1.5V

series battery

VCircuit diagramsymbol


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Voltage Homework 1. Read pages 47-50 in textbook2. Answer the Questions Below

1. What is electric potential? Use an analogy in your explanation____________________________________________________________________

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ _______

2. Copy Learn Section (the bit shaded grey) on page 53 of text below. ____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. What device is used to measure voltage (name and symbol)?________________________

____________________________________________________________________


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Series and Parallel Circuits

Bulbs in Series

Only one path for electrons

Bulbs ______ the voltage_____ so each glow

_______.

If one bulb is ____________the other ________ becausethe _____________.

http://phet.colorado.edu/simulations/si

Bulbs in Parallel

Two paths for electrons

Both bulbs get ______

voltage so both glow________.

Current is _____ in each______

If one bulb is

+ -

>

>

>Branch

Two

iTiT

i1 i1i2

i2 i2

i2

iT

iT

V

full

brightly

V

12V

12V

12V

sharedbulb /branch

removed/blown

stays on

there is still a complete path


15/94

Basic Circuit Rules Series Circuit

Current through___________ is_________________________.

Voltage _______ acrosseach resistor is

______________ to itsresistance.

Total voltage equals sum of

Parallel Circuit

Voltage drop across_________ is

________________________.

Current _______ each_______ is _____________

to its total resistance. current in

= Symbol for resistor

both resistorsthesame.

(theres only onepath!)Drop

proportional

100 200

V V

12V

4V 8V

100

200

both resistors

the

same.

(must go back with

0V)through branchproportional

Total the circuit

A

A

A

3A2A

1A

A

3A
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Short Circuits

In parallel circuits we can have _________ ___________ wewant.

However, if one of the branches consists only of a good__________ (no ______ or _______ of any kind) we will get a

______________.

Virtually _________ will flow through the branch with no______

This causes 2 things:

All of the other ____________________ go _____

An _________________ current in the __________branch

______ current = _____ heat = _______ or_______!!!

as many branches

conductor

loads devices short circuit

all current load

components / devces off

extremely large no - load

High High Sparks Fire


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Circuits Homework 1. Read pages 41-42 in textbook2. Answer Questions 1- 5 on pg 47-48

below________________________________________________________________________________________________________________________________________

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________ _______

____________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________


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Circuits Homework Contd____________________________________________________________________________________________________________________________________________________________________________________________________________

___________________________________________________________________________________________________________________________________________________________________ _______

____________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


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Resistance Resistance can be thought of as ________ current.

Resistance is measured in _______________.

All materials (even __________) have some resistance.Materials with low resistance are called ________. Those withhigh resistance are _________.

Factors that affect Resistance are:

1) Length: _________________

_______________________

2) Cross-sectional Area:

_______________________

_______________________

3) Material: ________________

4) Temperature: _____________

________________________

slowing

ohms ()

conductors

conductors

insulators

the longer thewire;the greater the

resistance

As area resistanceLike a highway; more lanes;more cars through

different properties

resistance

as temperature


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Resistance Contd

Resistors: devices made to specifically provideresistance. They are used to

________________. In complicated circuits,such as those in __________, ______, and

___________ used to keep ________ and_________ at specific levels needed for othercomponents (parts) to work properly.

Resistors can have a large range of afew_______ to _________ of ______.

1 kilohm (____) = _______

1 megohm (____) = ___________

reducecurrent computers

TVs mobilephones

voltage

current

Ohms ()

millions Ohms ()

1k 1000

1M 1 000 000


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Circuits


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Ohms Law

In circuits; current, voltage, and resistance arerelated.

We can make a circuit to discover thisrelationship.

We can also draw them with symbols:

Power Supply (Cell):_______

Wires (Conductors):_____Resistors:____________

Voltmeter:________ Ammeter:_________

Circuit Diagram:

What does a battery look

like?

V A

A

Ammeter mustbe connected inseries

V

Voltmeter must be

connected in parallel

Oh L
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Ohms Law Ohms Law: The ________ flowing through a circuit

(conductor) is __________ to the ________ _______between its ends.

V = _____

R = _____

I = _____

Ohms Law Problem: A circuit with a 12 resistor is connected to a 6Vpower supply. What is the current through it?

current

proportional potential difference

V

I R

IR

V/IV/R

Most commonform

Given: V = 6V

R = 12

I = ?

I = V/R

= 6/12

= 0.5A

Important:

Must use Proper Units:Voltage in VoltsCurrent in Amps

Resistance in OhmsIf not; you must convert first!


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Ohms Law Lab

Make a Circuit as shown and fill in the following charts:

Use Lab on page of booklet for method (we will use 56 and 330 resistorsso we can use bigger voltages then in the lab) Do it twice, once for each

PowerSupplySetting(Volts)

Voltmeter

Reading(V)

Ammeter

Reading(I)

V/I(ohm

s)

Resistance of

resistor(ohms)

2 V

4 V

6 V

8 V

10 V

12 V

PowerSupplySetting(Volts)

Voltmeter

Reading(V)

Ammeter

Reading(I)

V/I(ohm

s)

Resistance of

resistor(ohms)

2 V

4 V

6 V

8 V

10 V

12 V

A

V

Oh L L b C td
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Ohms Law Lab Contd Plot values from above graph and answer questions below:

1. Calculate the slope of the lines:______________________

2. What does the slope represent?_____________________

3. Explain the difference in slope of the lines.

_____________________________________________________

_____________________________________________________

Oh L H k


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________________________________________________________________________________________________________________________________________

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________ _______

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________

Ohms Law Homework 1. Read pages 53-59 in textbook2. Answer Questions 1- 4 on pg 56 below3. Answer Questions 1- 6 on pg 59-60 below

Oh L H k C td


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Ohms Law Homework Contd____________________________________________________________________________________________________________________________________________________________________________________________________________

___________________________________________________________________________________________________________________________________________________________________ _______

____________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Oh L H k C td


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Ohms Law Homework Contd____________________________________________________________________________________________________________________________________________________________________________________________________________

___________________________________________________________________________________________________________________________________________________________________ _______

____________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


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Electrical Power

Power is__________________________________.

Its unit is __________. (_______=__________)

A general equation for poweris:_______________

Electric devices have __________.

Kettle:____________ Iron:__________

TV:_______ Power Drill:__________ Lamp:___________

For circuits: Power = ______ x ______ or

_______

the rate at which energy is transformedWatts (W) Power Energy/Time

P = E/t or E = Pt

power ratings2400W (2.4kW) 1100W (1.1kW) 80 W

400W 60W

Voltage curren

t

P = VI

P d P i F


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Power and Paying ForElectricity Why the electrical power equation works: The equation P=VI works because of how the_______, _________, _________, and _______are related.

Consider the battery on the right: General Description:

Each coulomb of charge______ _________ fromthe _________.

___ coulombs of chargeleave the battery

___________

So ___ joules of ________

energy is convertedener ever

ScientificDescription:

PD = ________

Current =_____

Battery

Volt

ampere coulomb joule

5km

Distance =5km + 5km= 10km

Displacement = 0km(finished where hestarted)

start

>

> finish8km

6km Distance =8km+ 6km= 14km

Displacement =(82 + 62)= (64 + 36)

= 10kmN

S

W E NE

direction

Speed and Velocity


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Speed and Velocity We often use speed and velocity interchangeably; however

they are technically different.

Speed is the ___________ in __________ over ________. Speed = ________ ________ (_________). It is a __________.

Velocity is the __________ in ____________ over ________.

Velocity = ______________ ________. It is a

_______________. Example: Calculate the average speed and Average velocity of trip if it takes me 15 minutes?

Most common units are _______ and _______.

We need to be able to convert between these units, heres how: (Example 3;page 11)

change distance timedistance time S = d/t scalar

change displacement

time

displaceme

nt

time vector V=disp/t

Given:d = 14kmt = 15min

= 0.25hr

converttohours!

S = d/t

= 14/0.25

= 56km/h

disp = 10kmNEt = 0.25hr

v = disp/t

= 10/0.25

= 40km/hNE

km/h m/s

Convert 60km/h tom/sGetunitsright!!!

Distance = 60km= 60 000m

Time = 1hr= 60min = 3600sec

S = d/t= 60 000m/3600sec

= 16.67m/s

So, 60km/h = 16.67m/s

Shortcut:

m/s -> km/h x3.6

Km/h -> m/s 3.6

Average Speed


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Average Speed Think about your trip to school. You did not go at a ___________

speed. You stopped and started, sped up and slowed down. If

you looked at the speedometer of your car (or bus) it would tell youyour ______________ speed or how fast you are going at thatexact __________. So if we know the distance travelled and timetaken, we can only calculate the ______________ speed.

Examples: 1. What is the average speed of a train ride that goes fromShorncliffe to the City

(25km) in 45 minutes. Give your answer in km/h.

2. A man completes a 70km bike race with an average speed of 30km/h.How long did it take him?

constant

instantaneousmoment

average

S

d

t

Given:d = 25kmt = 45min

= 0.75hr

S = d/t= 25/0.75

= 33.33km/h

*** if we left as min; our unitfor speed would be km/min

Given:

d = 70kms = 30km/ht = ?

t = d/s

= 70/30= 2.33hr

*** 0.33hr = 0.33(60)= 20min

= 2hr 20min

Acceleration

v = final speed


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Acceleration Acceleration is the __________ in speed over ______.

___________ = _________________ _____. (___ = ________)

Deceleration occurs when speed _________ over time. It has thesame _______ as acceleration but has a _______________.

Its main unit is ________ per _______ ________ (_______)

Acceleration due to gravity is _________. This means that every

second its speed has increased _______ from the last. So, 1second after an object is dropped its speed is _________

2 seconds after its going ____________; 5 seconds after________

Examples:

change time

Acceleration final initial

speed

time a (v-u)/t

u = initial speed

decreasesunit negative sign

metres second squared m/s2

9.8 m/s2

9.8 m/s9.8 m/s

2(9.8) = 19.6m/s

5(9.8) = 49 m/s

A car increases it speed from 95km/h to 110km/h to

pass. It does this in 5sec. What is its acceleration inkm/h/s? In m/s2

u = 95km/hv = 110km/ht = 5s

a = (v-u)/t

= (110-95)/5

= 15/5= 3 km/h/s

3km/h/s = 3 3.6 = 0.83m/s2

A runner finishes at race travelling at 12m/s. He comes

to a stop after 3 sec. Whats his acceleration?

u = 12m/sv = 0m/st = 3s

a = (v-u)/t

= (0-12)/3

= -12/3= -4 m/s2

Cartoon Physics!


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Cartoon Physics!

Cartoon Physics!


55/94

Cartoon Physics!

Cartoon Physics!


56/94

Cartoon Physics!

Speed & Acceleration


57/94

Speed & AccelerationHomework

Read pages 7-11 of text and the cartoons in booklet

Complete all questions from Exercise 01 on pg.11 of text.___________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

___________________________________________________________________


58/94

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________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

________________________________________________________________


59/94

Feeling Forces

Forces and Acceleration are ____________________; weactually feel them the same way.

This is because a force is need to________________________. (RECALL: Acceleration is a

change in motion) OR:No force, no change in ________; no acceleration!

Also, the ________ the force; the ________ theacceleration.

So, force and acceleration are said to be________________.

If I push two trolleys, one empty and one filled withgroceries, with the same force; which one goes further?

_______________________.

very closely related

cause a change in motion

motionbigger bigger

proportional

Spring cartdemo!!!the empty trolley!

smaller

halved

Or, it takes a ________ force to accelerate a _______ objecth h f bj

greater heavier

li h


60/94

the at the same rate of a ________ object.

So, with a constant force; acceleration and mass are________ proportional

All this can be summarised with the following formula:

a = F/m (but it is more commonly given as _______)

This is Newtons Second Law of Motion!

__________________ experience a force dueto _____________ but dont continually ________because there is normally a ________

force from the ground or a desk If the supporting force is removed; all objects fall with an

__________________ of ____________ or _____________

So, the force due to gravity pulling a 100kg man to the Earth

is F = ma = (______)(___) = _____ (Force is measured in

lighter

inversely

F = ma

F = force (N)m = mass (kg)a = accel.(m/s2)

F

m aAll objects on Earth

gravity fall

supporting

acceleration

9.8m/s/s 9.8m/s2

100 9.8 980N Newtons (N)

We can also experience what is called a force.perceived


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We can also experience what is called a ____________ force.

This is because of _____________. This is the idea that all objectswill stay in their ______________________ unless acted up by anoutside force (Newtons ________ law of motion).

Examples: (fig 1.5a-b & train)

Just like how we are free to move around in a car or train; our_____________ ___________ can move around inside of us; This is whatgives you that funny feeling in your stomach when you_______________!!!

p

inertiacurrent state ofmotionfirst

internalorgans

fall suddenly

Cartoon Physics!


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Cartoon Physics!

Cartoon Physics!


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Cartoon Physics!

Feeling Forces Homework


64/94

Read pages 12 & 13 and cartoons above

Answer questions 1-6 on page 16 of text

______________________________________________________________________________________________________________________________

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

______________________________________________________________________________________________________________________________

g

Rollercoaster Forces


65/94

Rollercoaster Forces Rollercoaster designers use the concepts of ___________

along with changes in the direction of the track to_______________ different _______ on the riders.

These forces combine with the force of ___________(_________ always acts on objects to pull them

_______________________)

Forces in a Loop:

inertia

create

forces Recall: A change in direction requires aforce!

gravity gravity

toward the centre of theEarth

Gravity always actingdown

NOTICE:

Gravity always samemagnitude (since mass ofcart does not change)

Force of cart always acting

toward the centre of thetrack

Combining Forces


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g Forces are _______; so they have a ________ (size) and a

_______.

We use _____________ to represent forces (and all_________)

The _______ of the _______ is proportional to the ______ ofthe force

The ______ points in the _______________ of the force

To add vectors we _______ the two (or more) forces___________ to form a _______________.

This triangle is a __________ triangle so we can use_____________ theorem to calculate the ___________ of thecombined _____ force.

In senior physics you will also learn to use_________________ to calculate the net forces exact

.

vectors magnitude direction

arrows vectors

length arrow sizearrow direction

Big force to the right small force to theleft

align Tip-to-tail

Vector triangle

Right-angle Pythagorasmagnitude net

trigonometry

direction

ObjectA 3N

B 2N

A + B tip-to-tail

Net force = 5N

Object 5N

ObjectA 3NB 2N

A + B

Net force = 1N

Object1N

Situation 1: There are 2 forces acting on an object. The first is 25N acting South andthe other is 35N acting West. What is the magnitude of the resultant force?


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g g

Situation 2: There are 3 forces acting on an object. The first is 125N acting North, thesecond is 70N acting East, and the other is 35N acting West. What is themagnitude of the resultant force?

Mathematically Graphically

Mathematically Graphically

N

S

W E

Object

25N

35N

25N

35N

Net force =

= (1850)

= 43N SW

(352 + 252)

43N

Scale: 1cm = 10N of Force

2.5cm= 25N

3.5cm= 35N

4.3cm

Net force

= 4.3(10)= 43 N SW

Object70N

35N

35N

125N

= (15625+1225)= 130N NE

(1252 + 352)

125N

Net force =

Scale: 1cm = 35N of

*125/35

=3.6cm

3.6cm= 125N

2 cm =70N

1 cm =35N

3.7cm

Net force

= 3.73(35)

= 129.5 N NE

Combining Forces:


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Read pages 13-15

Answer questions 7-10 on page 16 of text

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Rollercoasters as Energy


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gyConverters #1

Rollercoasters are only powered ________________ of the

ride; to get them to _______________________________. Its the speed from the __________that keeps it going

after that!

Heres why: When an object is ______; it gains

____________________________

PE = _____ where: __ = ______ (in ___)

__ = ___________ due to ________(_______)

__ = __________ of the object (in __)

When an object is dropped it gains ________________ (___)

KE = (_____)/___ where: ___ = ______ (in ____)

at the

beginningthe top of the first hill/drop

first drop

lifted Gravitational PotentialEnergy

mgh mmass

kg

g acceleration gravity 9.8m/s2

h height m

Kinetic Energy KEmv2 2 m

masskg

v velocity speed m/s

Joules J

***Actually ALL forms of energy measured in

Ki ti P t ti l E


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Kinetic vs. Potential Energy

At the point of maximum potential energy, the car has minimumkinetic energy.

Examples:

C


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What did you notice about the kinetic energy of the twoobjects?

A rollercoaster car andpassengers is pulled upthe first hill of the track. Itsmass is 350kg and the hill

is 120m tall. Calculate thePE.

Calculate the KineticEnergy of the samecart/passenger combowhen it has a speed of

30m/s.

A cannon ball of mass1.25kg is fired. It has amuzzle velocity of 500m/s.Calculate its KE.

*Units allgood!

m =350kg

g = 9.8m/s2

h = 120m

PE = mgh

= 350(9.8)(120)= 411600J

m =350kgv = 30m/s

*Units allgood!

KE = mv2

2

= 350(30)(30)2

= 157500J

m =1.25kgv = 500m/s

*Units allgood!

KE = mv2

2

= 1.25(500)(500)2

= 156250J

*VerySimilar

*velocity/speed is squared so a small object travelling very fast canhave as much KE as a big object travelling slower

How do we get Joules for PE & KE when we multiply totally different thingstogether? Lets consider units.


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g

There are only a few _______ units (these are __________, _________,and ___________); the rest are combinations of these _____ units.

Lets Prove that PE and KE have the same unit:

PropertyMeasured SI Unit Notes on the Unit

Base kilograms metresseconds Base

Height/distance/length Metre (m) SI Base Unit

Mass Kilograms (kg) SI Base Unit

Time Seconds (s) SI Base Unit

Speed/velocity Metres/second (m/s) A combination of base units

Acceleration Metres/second2(m/s2)

A combination of base units

Force Newtons (N)Given a special name but still a combinationof base units (1N = 1kgm/s2)

Energy Joule (J)

Given a special name but still a combination

of base units (1J = 1kgm2/s2)

PE = mgh

= kg (m/s2)(m)

= kgmms2

= kgm2

s2

KE = mv2

2No unit so we can leave it out

= kg (m/s)(m/s)

=kgmm

ss = kgm2

s2

Rollercoasters as Energy Converters #1 Homework:R d 19 21


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Read pages 19-21

Answer questions 1-3 on page 25 - 26 of text

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o ercoas ers as nergyC t #2


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gyConverters #2

As an object falls; its height obviously _____________. So,its PE also ______________.

But as it falls; its speed ____________. So, its KE_____________.

When an object falls; its PE is ________________to KE. Ifwe add the ___ and ___ of a falling object at any point of its

fall (just after release, half way down, just before contactwith ground); we will get ______________________.

We can use this knowledge to _______ the carts velocity from theearlier example at the bottom of the hill.

We know that at the bottom of the hill PE = ____ and at the top ofthe hill KE = ____ (just before it begins to fall)

So, this means _________ = _________ & __________ =__________

Example: Calculate the velocity of the cart at the bottom of the hill.

decreases

decreases

increases increases

constantlyconvertedPE KE

the same number

predict

0J

0JPEBOT KETOP PETOP KEBOT

KEBOT = PETOP =411600Jm =

350kgv = ?

KE = mv2

2

2KE =2

2(411600) = 350v2

v2 =823200/350

v=(2352) = 48.5m/s

But this this isnt exactly what happens inReal life


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But this this isn t exactly what happens in ______________.

If you were to touch the wheels of the cart what did you think youwould notice? _______________________

This is because of __________. _________ is a force that____________ motion and is present whenever two_____________________________. Friction causes _______and _______ is a form of __________. So some of the PE is

_____________ to heat. (Not all converts to ____)

You can also _________ the rollercoasters wheels rolling over thetrack. Sound is a form of ________ so some of the PE is alsoconverted to sound.

This is represented

in the graph:

Real life

They are

HOT!!! friction Friction opposesSurfaces move over eachotherheat heat energy

converted

KE

hearenergy

Cartoon Physics!


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y

Cartoon Physics!


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y

Rollercoasters as Energy Converters #2 Homework:


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Read pages 21-25 and cartoon physics

Answer questions 4-7 on page 26 of your textbook.

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Topic Review C l t ll ti (1 21)


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Topic Review: Complete all questions (1-21) on pages31-33

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Rollercoaster Investigation


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g Sketch of Track (Label the key dimensions):

Mass of car:

________________

Name of Section Section

Length

Key Heights

Rollercoaster Analysis I: Finding Speed & Velocity using Distance, Displacement and Time.


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Finding Speed & Velocity using Distance, Displacement and Time. Use the video to get times; distances and displacements by taking measurements directly from the

rollercoaster.Entire Rollercoaster

Average Speed Average Displacement

Track Section: First Drop

Average Speed Average Displacement Instantaneous Speed at end of drop

Track Section: Loop

Average Speed Average Instantaneous Speed at top of loop Instantaneous Speed at end of loop


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Average Speed AverageDisplacement

Instantaneous Speed at top of loop Instantaneous Speed at end of loop

Track Section: Second Hill

Average Speed Average Displacement Inst. Speed at top of 2nd Hill Inst. Speed at end of 2nd Hill

Track Section: Flat

Average Speed Average Displacement Instantaneous Speed at end of Flat


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Extra Work Space:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Average Speed Average Displacement Instantaneous Speed at end of Flat

Rollercoaster Analysis II: Finding Speed & Velocity using Energy.


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Finding Speed & Velocity using Energy.

Entire Rollercoaster

PE & KE at Start of Track PE & KE at End of Track Energy Lost Energy Lost per cm of Track

Track Section: First Drop

PE at Start and End of Sectoin KE at Start and End of Section (includeLosses)

Speed at End of Section (Average orInst?)

Track Section: Loop

PE at Start, Top, End of Loop KE at Start, Top, End of Loop Speed at Top and End of Loop


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Track Section: 2nd Hill

PE at Start, Top, End of 2nd Hill KE at Start, Top, End of 2nd Hill Speed at Top and End of 2nd Hill

Track Section: Flat

PE at start and end of flat KE at the start and end of flat Speed at end of Flat


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Extra Work Space:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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p

Discussion Questions: 1. Complete the table:

Point on Track Speed (Method I) Speed (Method


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2. Discuss any differences. Which method do you think was more accurate, why?.____________________________________________________________________________________________________________________________________

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Point on Track Speed (Method I) Speed (MethodII)

End of First Drop

Top of Loop

End of Loop

Top of 2nd Hill

End of 2

nd

HillEnd of Flat

3) What are the advantages and disadvantages of each method?___________________________________________________________________


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4) Consider the Energy v Length of Track graph from below. Using all theinformation gathered using Method II (PE and KE) complete one of these for ourcoaster.

Energy Changes Over a Rollercoaster Track


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2011 10 Physics Power Point New

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