TAKS Objective 5

Motion , Forces

and Energy

Energy

Is defined as the Ability to do Work

Energy has Two

Types: Kinetic (Energy of Motion) Kinetic (Energy of Motion) and and Potential (Stored Energy)Potential (Stored Energy)

Kinetic Energy

KE = ½ m v 2 Ex: A moving car

has the ability to

do work on the light pole if it hits it.

Gravitational Potential Energy

or Will it fall?

GPE = m g h

m is the mass of the

object in Kg,

g is the acceleration

due to gravity which is

9.8 m/s2 on earth and

h is the height in meters

Use the formula page! PE = mgh

41 What is the potential energy of the rock?

A 59,900 joules

B 64,600 joules

C 93,100 joules

D 121,600 joules

m = 95 kg g = 9.8 m/s2 h = 100 m

95 kg x 9.8 m/s2 x 100 =

93,100 joules C

Electrical Energy - Moving electrons in a path is electricity

Electrical Potential Difference (v) is measured in Volts The rate of moving electric charges, Electric Current

(I), is measured in Amperes Resistance or opposition to the movement of the

energy is called Resistance (R).

Circuits – 2 types

Series circuits are the most simple.

One (1) path for the current to travel.

Contains an energy source, a path, and a load (something for it to do, like a lamp)

Circuits – 2 types Parallel circuits

provide more than one path for the current to travel.

Most circuits are parallel, since if one lamp goes out, the others can stay lit.

F. QG. RH. SJ. T

6. Which switches, if opened, will cause the light bulb to stop

glowing?

It is the only switch in series to both the battery and light.

USE THE FORMULA SHEET!!

What is the current in a copper wire that has a resistance of 2 ohms and is connected to a 9 volt electrical source?

A. 0.22 amp

B. 4.5 amps

C. 11.0 amps

D. 18.0 amps

V = I R so,

9V = I x 2 ohms or 4.5 amps

Heat- Transfer of Thermal Energy

1. Conduction-direct contact, a pot heating on a stove (solids)

2. Convection- heating by circulating fluids, (gas and liquid) heating from a fireplace

And. . .

Three forms of heating:Three forms of heating:

3. Radiation – Transfer of Electromagnetic (E.M.) Energy

Objects are heated when exposed to infrared radiation

The suns heats the earth by sending infrared radiation along with other forms of E.M. energy 3.0 x 108 meters through empty space

Heat moves by conduction in solids since the particles are close together and vibrate. . .

43 Heat convection occurs in gases and liquids. Heat convection does not occur in solids because solids are unable to —

A absorb heat by vibrating

B transfer heat by fluid motion

C emit radiation by reflecting light

D exchange heat by direct contact

Solids do radiate heat to their surroundings

2 The primary way liquids and gases transmit heat is by the process of —

F reflection

G conduction

H radiation

J convection

Fluid heat movement is convection. Fluid motion occurs in liquids and gases.

F improve emission of infrared radiation

G reduce the heat loss by convection currents

H improve absorption of infrared radiation

J reduce the heater’s conducting properties

50 A solar heater uses energy from the sun to heat water. The heater’s panel is painted black to —

Emission is giving off – we want to absorb: Not F

Convection is movement of heat in fluid matter, heat loss would be from a solid exterior – Not GPainting a substance will not change its conductivity

– That is a property of metals. It would have to be made of a different substance to change that: Not J

Waves - Energy carried by rhythmic disturbances

Two types: 1. E.M. radiation

move through empty space

2. Mechanical require a medium (air, water or any type of matter) for movement

Waves - 2 Types

All waves have similar properties

Frequency- the number of vibrations per second or the speed of the movement of the vibrating particles

Amplitude – the size of the movement of the vibrating particles

Both are controlled by the disturbance that created the waves

Velocity of all waves - v=f λ

f-frequency and λ is wavelength (distance between identical points on two consecutive waves)

Reflection- bounce off barriers in regular ways

Refraction- waves can change direction when speed changes

And the answer is?

38 At 0°C sound travels through air at a speed of 330 m/s. If a sound wave is produced with a wavelength of 0.10 m, what is the wave’s frequency?

F 0.0033 Hz

G 33 Hz

H 330 Hz

J 3300 Hz

Use the formula chart!!!

Velocity = f λ OR f λ OR

330 m/s = f x 0.10 m330 m/s = f x 0.10 m

JJ 3300 Hz 3300 Hz

Sound Waves move through matter not through empty space.

32 One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because of —

F interference

G the Doppler effect

H resonance

J standing waves

Resonance is the vibration of another object struck by a wave of the correct frequency. Since the forks are identical, the second one receives the correct frequency to begin vibrating.

Forces and Motion Forces can create

changes in motion (acceleration)

Deceleration is negative acceleration

Velocity Graphs V = distance

time

Velocity (v) is the slope (rise over run) of a position (d) vs. time (t) graph

Velocity

0

20

40

60

1 3 5 7 9 11 13 15

Time (sec)

Dista

nce (

m) Series1

Series2

40 The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed?F QG RH SJ T

How do we work this one?

Calculate v = d/t for each segment.

Acceleration Graphs Acceleration (a) is

the slope of a velocity (v) vs. time (t) graph

Plotted on a distance vs. time graph, acceleration is an exponential curve

Acceleration

0

20

40

60

1 3 5 7 9 11 13 15

Time (sec)

Velo

city

((m

/s)(m

)

Acceleration is a change in an objects velocity (speed or direction)

When an object’s speed changes over time it is accelerating (or decelerating)

A = vfinal – vinitial time Units for acceleration

m/s/s or m/s2

Definition of a Force

A Force is a push or a pull

Balanced Force

A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.

4 The picture shows the position of a ball every 0.25 second on a photogram. Using a ruler, determine the velocity of the ball.

F 3.5 cm/s

G 10.5 cm/s

H 14.0 cm/s

J 28.0 cm/s

Use the ruler on the side of the chart and the equation for velocity. The answer was H.

Measure from the center of ball 1 to the center of ball 2 and divide by .25.

Unbalanced Forces

Are forces that results in an object’s motion being changed.

+

Friction

A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

Friction

Friction causes an object to slow down and stop.

Since the amount of energy stays constant, the energy becomes heat.

Newton’s 1st Law of Motion

Object in motion stays in motion

Newton’s 1st Law of Motion

And Objects at rest stay at rest

Newton’s 1st Law of Motion

Until they are acted upon by unbalanced forces.

Inertia or Newtons 1st Law

Tendency for an object to stay at rest or moving in a straight line at a constant speed.

The mass (m measured in kg) of an object determines its inertia

Newton’s 2nd Law of Motion

Force = Mass X AccelerationF=maWeight (pull of gravity) is a commonly measured force,

calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2

Newton’s 2nd Law of Motion

The greater the mass of an object, the greater the force required to change its motion.

Newton’s 2nd Law of Motion

The greater the acceleration of an object, the greater the force required to change its motion.

A 0.2 N B 0.8 N C 1.5 N D 6.0 N

11 The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping?

Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2.

So, .5 kg x 3 m/s2= 1.5 N

Newton’s 3rd Law of Motion

For every action force there is an equal and opposite reaction force.

Newton’s 3rd Law of Motion

All forces come in action-reaction pairs

Ex: feet push backward on floor, the floor pushes forward on feet

27 A ball moving at 30 m/s has a momentum of 15 kg·m/s. The mass of the ball is —

A 45 kg

B 15 kg

C 2.0 kg

D 0.5 kg

Formula Page says that Momentum = Mass x Velocity

So 15 kg.m/s = M x 30 m/s solving for M it is:

Work Work: using a force

for a distance W = F x d The work done by forces on an object

= changes in energy for that object. Work and Energy are measured in

Joules 1 Joule=1 Newton • meter

42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?

F 300 JG 750 JH 1,000 JJ 15,000 J

Use the formula Work = Force x distance

Force of 20 N x 15 meters = 300 Joules Answer:

Machines make work easier

The ideal mechanical advantage of a machine (IMA) of a machine is the number of times the output force is larger than the input

force IMA=Fout/Fin A machine can only make this

happen by moving the input force through a farther distance than the output force

Fin • din=Fout • dout

48 The diagram shows an electric motor lifting a 6 N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat?

F 9 J

G 12 J

H 18 J

J 21 J

Work Output = Resistance Force x Resistance Distance

Workout = 18J = 6N x 3m

Work Input = 30J done by the motor

The difference is lost as heat due to friction, which is 30J – 18J = 12J

Answer G

Real Machines use Energy No real machine is

100 % efficient. i.e. none put out more work than is put in

Efficiency of a machine is work output/work input X 100 %

Eff = Wout X 100%

Win

Machines use power Power: the rate at

which energy is used (work is done)

P=Work/time Power is measured in

H.P. or watts 1 watt = 1 Joule

1 sec

A accelerated rapidly

B remained motionless

C decreased its velocity

D gained momentum

45 If a force of 100 newtons was exerted on an object and no work was done, the object must have —

Work = Force x Distance

Work = 0 Force = 100 N so

0 J = 100 N x d

distance must be 0

It did not move!

Universal Law of Gravitation

All objects in the universe attract each other by the force of gravity

Universal Law of Gravitation

Gravity varies depending on two factors:

1) the mass of the object doing the pulling, and

2) the distance from the center of that object

On Earth gravity = 9.8 m/s/s

For every second that an object falls its speed increases by 9.8 m/s

Weight= Mass (m) X gravity (g)

Weight Unit of mass = kg Unit of acceleration =

m/s/s Unit of weight = Newton 1 Newton= about ¼ pound