 # Energy Changes 2

In this worksheet, students learn about energy changes, the work needed for changes to happen and dissipation of energy. Key stage:  KS 4

Curriculum topic:  Physics: Energy

Curriculum subtopic:  Energy Changes

Difficulty level:   ### QUESTION 1 of 10

In order for energy to change from one form to another, work needs to be done. Work is done on an object when a force acts to move an object in the direction of the force, even if movement does not take place.

Dissipation is the loss of energy as it is transferred to a different form from the initial one. The new type of energy is not capable of doing work as much as the initial one, that's why we say it is lost.

When you kick a ball, you give it kinetic energy, which makes it move. After a while, air resistance and friction act against the direction of the movement and slow the ball down, because it has to do work against these forces. Kinetic energy is dissipated to heat energy. Objects that are above the Earth's surface have gravitational potential energy (GPE). For example, if you cycle up a hill without pedalling, the kinetic energy of you and the bicycle, as a system, will eventually drop, so you slow down. To prevent stopping you need to pedal as you go up, which means you need to do work against the gravitational pull of the Earth. Just as you reach the top of the hill, a lot of your kinetic energy will have changed to GPE. Work is essentially the amount of energy that has changed form. This can be calculated using the following formula:

work  =  force  ×  distance travelled

The force is measured in Newton (N) and the distance in metres (m). The unit for work is Joules (J).

What is needed for energy to change from one form to another?

What is a usual outcome of work?

An object moves in the opposite direction of a force.

An object moves in the direction of a force.

The effect of work is not obvious usually.

What is the scientific word for loss of energy when it is transferred from one form to another?

What forces act against the direction a ball moves in after it has been kicked?

gravity and upthrust

friction and the force from the kick

friction and air resistance

What does dissipation of energy involve when a ball is moving?

Heat is transferred into kinetic energy.

Kinetic energy is transferred into heat.

GPE is transferred into kinetic energy.

Why does the ball lose its kinetic energy?

because it needs to do work against gravity

because it needs to do work against the force of the kick

because it needs to do work against friction and air resistance

When a crane lifts a vehicle, it does work. How much work is needed if the crane is to lift a heavier car?

The amount of work remains the same.

The amount of work increases.

The amount of work decreases.

Why does work need to be done when one cycles up a hill?

Without work the bicycle will eventually move downwards.

Work is needed so the bicycle speeds up.

Without work the cyclist will fall off the bicycle.

Why would the cyclist not make it to the top of the hill without work?

because of upthrust

because of air resistance

because of the gravitational pull of the Earth

A total force of 20 N is acting against the movement of a skier travelling down a slope for 100 m. Calculate the work needed to keep the skier moving down hill.

5 J

200 J

2000 J

• Question 1

What is needed for energy to change from one form to another?

work
EDDIE SAYS
Work needs to be done for energy to change from one form to another.
• Question 2

What is a usual outcome of work?

An object moves in the direction of a force.
EDDIE SAYS
As a result of work, an object moves in the direction of a force.
• Question 3

What is the scientific word for loss of energy when it is transferred from one form to another?

dissipation
EDDIE SAYS
Dissipation is the loss of energy when it is transferred from one form to another.
• Question 4

What forces act against the direction a ball moves in after it has been kicked?

friction and air resistance
EDDIE SAYS
Friction and air resistance act against a ball moving.
• Question 5

What does dissipation of energy involve when a ball is moving?

Kinetic energy is transferred into heat.
EDDIE SAYS
When a ball is moving, kinetic energy is transferred into heat and so the ball slows down and eventually stops.
• Question 6

Why does the ball lose its kinetic energy?

because it needs to do work against friction and air resistance
EDDIE SAYS
A ball that has been kicked and is moving loses kinetic energy, because it needs to do work against friction and air resistance.
• Question 7

When a crane lifts a vehicle, it does work. How much work is needed if the crane is to lift a heavier car?

The amount of work increases.
EDDIE SAYS
Cranes need to do more work when they lift heavier objects.
• Question 8

Why does work need to be done when one cycles up a hill?

Without work the bicycle will eventually move downwards.
EDDIE SAYS
When cycling up a hill work needs to be done, so that upward movement continues to reach the top of the hill. Without work the bicycle will eventually move downwards.
• Question 9

Why would the cyclist not make it to the top of the hill without work?

because of the gravitational pull of the Earth
EDDIE SAYS
The cyclist would not make it to the top of the hill without work because of the gravitational pull of the Earth.
• Question 10

A total force of 20 N is acting against the movement of a skier travelling down a slope for 100 m. Calculate the work needed to keep the skier moving down hill.