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8th Grade Science

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Work, Power and Machines

Energy and Heat

Waves and Sound

Electricity and Magnetism

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Row 1, Col 1

What is the purpose of a simple machine?

To make work easier.

1,2

This is the energy of a moving windmill.

Mechanical Energy

1,3

What is the difference betweena mechanical and

an electromagnetic wave?

A mechanical wave requires a medium, an electromagnetic wave does not.

1,4

This is the difference betweena radio and a gamma ray in

terms of frequency, wavelengthand speed.

A radio wave has a longer wavelength and lower frequency than a gamma ray but both travel at the same

speed.

2,1

What are the 3 ways that a machinecan make work easier?

The machine could change the direction of the input force, increase the output force by reducing the input distance or increase the output distance by reducing

the input force.

2,2

How much potential energy does

a 50 N box have if it is sitting

5 m above the floor have?

PE = W x H

PE = 50 X 5

PE = 250 J

2,3

This property explains why alight wave bends when it enters

a new medium.

Refraction

2,4

When a circuit is open are thelights on or off?

Off

3,1

How much work does a man do when he pulls ona heavy cabinet with a force of 50 N and the

cabinet still does not move?

None – in order for work to be done the object must move in the direction of the force.

3,2

This is the movement of thermal energy from one object

to another.

heat

3,3

Because only red light is beingtransmitted, all other colors are

being absorbed.

Why does a red transparent water bottle appear red?

3,4

What will happen to the circuit below if a bulb is added?

The brightness will remain the same but the battery will drain faster.

4,1

How does a doorknob (wheeland axle) make work easier?

It allows you to use less force over a greater distance

4,2

You have a pot and bowl of soupat the same temperature. Whichhas more thermal energy? Why?

The pot because thermal energy is total kinetic energy and the pot has more mass so it will have more total

energy.

4,3

A high pitch, soft sound suddenly becomesloud and low pitch. Explain how the

properties of the wave must have changed.

The amplitude becomes higher and the frequency decreases.

4,4

Give an example of charging by friction and induction.

Friction – rubbing a balloon in your hairInduction – the now charged balloon can cause charges

to rearrange within another object without direct contact.

5,1

How much work does a man do if he lifts a 100 kg box

0.5 meters off of the table?

W = f x d

W = (100 x 9.8) x 0.5

W = 490 J

5,2

A 240 kg skier flies down the hill at10 m/s. What is her kinetic energy?

KE = ½ mv2

KE = ½(240)(10)2

KE = 12,000 J

5,3

What is the frequency of a wave that has a wavelength of 3 meters, amplitude of 2 meters

and a speed of 21 m/s.?

F = S/WF = 21/3F = 7 Hz

5,4

What is the device above called, how could it be strengthened?

A solenoid, add an iron core or more coils.