TAKS Objective 5

The student will demonstrate an understanding of motion, forces,

and energy.

Practice filling in

• Speed is the rate of change in position

• V = d t

– V = velocity– d = distance– t = time

Speed

V = d t

Set up the Speed Triangle

d

tv

v = v = dd

tt

Sometimes the question will use the word VELOCITYVELOCITY instead of speed.

A 1-kilogram ball travels 50 meters in 5 seconds. The velocity of the ball is —

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Speed = 56 meters 96 sec

Speed = 0.58 m/s

d

tv

• Velocity is the speed and direction of an object

• The velocity of an object can change even if the speed remains constant

Velocity & Speed

• Acceleration is the rate of change of velocity–Speeding up –Slowing down

Acceleration

vf - vi

a = -------- t

vf = final velocity

vi = initial (beginning velocity)

a = accelerationt = time

Equation to find Acceleration

vf - vi

ta

vf - vi

a

Grade 10 2009

a = (30 m/s) – (20 m/s)2 seconds

a = (10 m/s) 2 s

a = 5 m/s2

t

vf - vi

a

• Forces are all around us– Pushing– Pulling– Squeezing

What is a force?

• Momentum can be defined as "mass in motion.”

• Momentum depends upon the variables mass and velocity

• Momentum = mass x velocity • p = m x v

– m = mass– v = velocity– p = momentum

Momentum

p

vm

• Describe the momentum of a 5-kg bowling ball moving westward at 2 m/s.

• p = m x v• p = 5 kg x 2 m/s• p = 10 kg x m/ s

Momentum

p

vm

Grade 10 2009

p = mvp = 2.0 kg x 15 m/sp = 30 kg • m/s

p

vm

p = m x vp = 0.2 kg x 12 m/sp = 2.4 kg • m/s

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p

vm

Energy is the amount of work a physical system is capable of

performing.

The Law of Conservation of Mass states:

Energy can neither be created nor destroyed

A measure of the change a force produces.

The work done by a force acting on an object is equal to the force multiplied by the distance through which the force acts.

FdW W

dF

Work is done……by a force when the object it

acts on moves a distance

NO work is done by pushing against a wall that will not move.

Work IS done throwing a ball because the ball MOVES while being pushed during the throw.

joule (J) The SI unit of energy

Amount of work done by a force of one Newton when it acts through a distance of one meter:

PRACTICE PROBLEM #1PRACTICE PROBLEM #1

A person pushes a large box across a level floor by applying a horizontal force of 200 N. If the person pushes the box a distance of 5 meters in 10 seconds, how much work does the person do on the box?

A 2000 joules

B 1000 joules

C 400 joules

D 100 joules

Work =force x distance

W=F x dW= (200N)(5m) = 1000 joules

W

dF

The weight lifter used a force of 980 N to raise the barbell over her head in 5.21 seconds. Approximately how much work did she do in raising the barbell?

F 380 JG 982 JH 2,000 JJ 10,000 J

(Practice problem from TEA released TAKS Test)

W=F x dW= 980N x 2.04m =1999.2J

W

dF

The RATE of Doing Work… Power is the amount of work done in a

specified period of time The more powerful something is, the faster it

can do work

time

WorkPower W

tP

A mechanic used a hydraulic lift to raise a12,054 N car 1.89 m above the floor of agarage. It took 4.75 s to raise the car.

Whatwas the power output of the lift?A 489WB 1815WC 4796D 30,294W

 

(Practice problem from TEA released TAKS Test)

P=W / tW = F x d W=12,054N x 1.89m = 22,782.06J

P= 22,782.06J/4.75s=4,796.2W

W

tP

Day 2Day 2Newton’s Three Laws, Simple Machines, & Waves

11stst Law of Motion Law of Motion (Law of Inertia) (Law of Inertia)

An object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an unbalanced force.

11stst Law Law Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

What is one type of What is one type of unbalanced force that unbalanced force that acts on an object in acts on an object in motion?motion?

FrictionFrictionSlide a book

across a table and watch it slide to a rest position. The

book comes to a rest because of

friction.

Newton’s 1Newton’s 1stst Law and You Law and You

Don’t let this be you. Wear seat belts.

Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving forward at 80 km/hour.

Grade 10 2009

22ndnd Law Law

The force of an object is equal to the product of

its mass and acceleration, or

F=m x a.

22ndnd Law Law

22ndnd Law Law

How much force is needed to accelerate a 1400 kilogram car 2 m/sec2?

F = m x a

F = 1400 kg x 2 m/sec2

2800 NF

am

Check Your UnderstandingCheck Your Understanding

1. What acceleration will result when a 12 N net force is applied to a 3 kg object?

F = m x a

a = F = 12 N = 4 m/sec2

m 3 kg

 

F

am

Check Your UnderstandingCheck Your Understanding

2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2.

Determine the mass.

F = m x a

m = F = 16 N = 3.2 kg a 5 m/s2 F

am

Check Your UnderstandingCheck Your Understanding

3. How much force is needed to accelerate a 66 kg skier 1 m/sec2?

F = m x a

F = 66 kg x 1 m/sec2 F

am

Check Your UnderstandingCheck Your Understanding

4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec2?

F

am

F = m x a

F = 1000 kg x 9.8 m/sec2

F = 9800 NF

m

F = (6.0 kg) x (0.50 m/s2)

F = 3 kg • m/s2

W = (3 kg•m/s2) x (8.0 m)

W = 24 Nm

33rdrd Law LawFor every action, there is an equal and opposite reaction.

33rdrd Law LawWhen you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

33rdrd Law Law

The hot gases The hot gases push down push down against the against the

ground. As the ground. As the gases move gases move

downward, the downward, the rocket moves in rocket moves in

the opposite the opposite direction, direction, upward.upward.

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What is a Simple Machine? A simple

machine has few or no moving parts.

Simple machines make work easier

Wheels and Axles

The axle is a rod that goes through the wheel which allows the wheel to turn

Gears are a form of wheels and axles

Pulleys

Pulley are wheels and axles with a groove around the outside

A pulley needs a rope, chain or belt around the groove to make it do work

Inclined Planes

An inclined plane is a flat surface that is higher on one end

Inclined planes make the work of moving things easier

Wedges

Two inclined planes joined back to back.

Wedges are used to split things.

Screws

A screw is an inclined plane wrapped around a shaft or cylinder.

The inclined plane allows the screw to move itself when rotated.

Levers-First Class

In a first class lever the fulcrum is in the middle and the load and effort is on either side

Think of a see-saw

Levers-Second Class

In a second class lever the fulcrum is at the end, with the load in the middle

Think of a wheelbarrow

Levers-Third Class

In a third class lever the fulcrum is again at the end, but the effort is in the middle

Think of a pair of tweezers

There are also two kinds of work to be considered when a machine is used. Work done on the machine – Win (work

input) Work done by the machine – Wout (work

output)

You can never get more work out of a machine than you put in.

Wout can never be greater than Win

Mechanical Advantage

The number of times a machine multiplies the effort force is the mechanical advantage (MA) of the machine.

MA = work output work input

wo

wiMA

Efficiency

Efficiency is a measure of how much of the work put into a machine is changed to useful work put out by a machine.

The higher the efficiency, the greater amount of work input that is changed to work output.

600 N x 2.5 m = 1500 Nm

300 N x 6.5 m = 1950 Nm

1500 Nm 1950 Nm

X 100 = 77%

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WAVESWAVES

A transverse wave is a wave in which the particles of the medium move in a 90 degree angle to the direction of energy transport.

The crest of a wave is the highest point of the wave.

The trough of a wave is the lowest point of the wave.

The amplitude of a wave refers to the amount of energy carried by a wave.

A longitudinal (compressional) wave is a wave that moves in the same direction as

the medium it is traveling through.

Wavelength – the distance from a point in a wave to the next point that wave in the same place.****From crest to crest or trough to trough

• Frequency – the number of complete waves passing a point per second

How many cars pass the line in one second?

By knowing the frequency of a wave and its wavelength, we can find its velocity.

Here is the equation for the velocity of a wave:

velocity = wavelength x frequency or

v = x f

f

v

Wave Properties: Reflection

When a wave hits a barrier, it will be reflected depending on the direction of the barrier (normal).

• Refraction causes objects to appear in a different place than it actually is because when light passes into a different medium the light path bends.

Wave Properties: InterferenceWhen two waves travel through the same medium and collide.

1. Constructive interference is when the amplitudes of the initial waves are in the same direction. The resulting wave will be larger than the original waves.

Constructive Interference

2. Destructive interference is when the amplitudes of the initial waves are opposite.

Destructive Interference

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Wave Properties: Resonance

• Resonance - VIBRATIONS.

Grade 10 2009

Energy, Heat & Circuits

Types of Energy

Kinetic – Energy of Motion Potential – Energy of Position

Chemical Energy Food converted to energy in our bodies

Heat Energy Heat from burning oil to make steam to drive turbines

Electric Energy Electricity turns motors in homes and factories

Radiant Energy Energy from the sun

Kinetic Energy

Kinetic energy = the energy an object possesses due to its motion

Kinetic energy = ½ mv2

Kinetic Energy

Kinetic energy of a 1000kg car moving at 10 m/s is 50kJ

Potential Energy

Energy stored in an object.

Gravitational Potential EnergyWhen a stone is dropped, it falls towards

the ground, until it hits the ground

Potential Energy Gravitational Potential energy =

the energy an object possesses because of its position relative to the ground

h mg

Gravitational

Potential = mgh Energy

Potential Energy Example Potential energy of a car pushed

off a 45m cliff

kJmsmkgmghPE 441)45)(/8.9)(1000( 2

Conservation of Energy

Law of Conservation of Energy:Energy cannot be created nor

destroyed, although it can be changed from one form to another.

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Temperature and Heat

Thermal energy: the total potential and kinetic energy of the particles of a material.

Heat is thermal energy in motion.

Methods of Heat Energy Transfer Conduction is the transfer of heat energy by

direct contact Convection is the transfer of heat energy by

the movement of fluids(gas or liquid) currents.

Radiation is the transfer of heat energy by electromagnetic waves

A. Conduction transfers energy as heat along the wire and into the hand

B. Embers swirl upward in the convection currents that are created by the warmed air above the fire which rises

C. Electromagnetic waves emitted by the hot campfire transfer energy by radiation

Heat Transfer by Conduction

Conduction is the transfer of thermal energy by direct contact of an object to a heat source.

When a metal poker is put in a hot fire, the exposed end of the poker soon becomes hot as well. We say that heat has been conducted from the hot end to the cold end.

Heat Transfer by Convection Convection is the process

of heat transfer through the mass motion or flow of some fluid, such as air or water. When a pot of water is heated,

convection currents are set up as the heated water at the bottom of the pot rises because of its reduced density and is replaced by cooler water from above.

Heat Transfer by Radiation

Radiation is a more rapid transfer of thermal energy in the form of electromagnetic radiation. The warmth you fell when you warm yourself

by a fire is due to this radiation. If the object is hot enough, some of the radiation is visible and can indeed be seen.

What type of heat transfer is shown in the following pictures?

A.

B.

C.

D.

Convection

Radiation

Radiation

Conduction

Grade 10 2009

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Conductors and Insulators

Conductors readily transfer heat energy.

Insulators are poor conductors of heat energy.

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CircuitsCircuits

Circuit DiagramsCircuit DiagramsA circuit diagram is a drawing of a real circuit, allowing you to see the direction of flow of electricity.

Basic Parts of a CircuitBasic Parts of a CircuitSwitch – can be used to turn

circuits on and offWires – for the current to run

throughPower Source – for example a

battery

Switch

Battery

Wires

Light Bulb

Open & Closed CircuitsOpen & Closed CircuitsWhen a circuit is turned off, it is

called an open circuit, because it has a break in it or the switch is open.

When there are no longer any breaks in the circuit, it is called a closed circuit, and the electricity will flow through the circuit.

Open CircuitOpen Circuit

Closed CircuitClosed Circuit

Two Types of CircuitsTwo Types of Circuits1. Series Circuit

2. Parallel Circuit

Series CircuitSeries CircuitIn a series circuit, the current can

only take one path.All the current flows through

every part of the circuit.◦Christmas Lights – if you remove one

bulb and the whole strand goes out, then they were made in series.

Series CircuitSeries Circuit

Only one path to follow!

Parallel CircuitsParallel Circuits

In parallel circuits, the current can take more than one path. ◦The electrical circuits in homes and buildings are parallel circuits

Parallel CircuitParallel Circuit

MORE than one path to follow (THREE)!

2009 Grade 10

CurrentCurrent

Current is the flow of electrical charges.

Current is measured in amperes.

ResistanceResistance

Resistance (R) is a measure of how difficult it is for the charges to flow through the wire.

Ohm’s LawOhm’s LawOhm’s Law states that the

current of a circuit is the ratio of the voltage and the resistance of the circuit.

I = V / R◦I = current (amps)◦V = voltage (volts)◦R = resistance (ohms)

V

RI

Practice ProblemPractice Problem

In this circuit, how much current flows through the light bulb?

A 0.75 ampB 1.50 ampsC 2.0 ampsD 3.0 amps

CurrenCurrentt = = voltage voltage = = V V resistance R resistance R

Current = Current = 1.5 volts1.5 volts = = 0.75 0.75 ampamp

2.0 ohms 2.0 ohms