# Force and Displacement

In this worksheet, students will learn about work done by a force and how to calculate it using the displacement it causes.

Key stage:  KS 3

Curriculum topic:   Physics: Energy

Curriculum subtopic:   Energy Changes and Transfers

Difficulty level:

### QUESTION 1 of 10

The diagram shows a fist displacing water as it punches into it with force.

Forces can cause displacement of objects and this is called work done by the force on the object. When a book falls off a table, gravity acts on the book and causes it to be displaced from the table to the floor. This means work was done on the book.

When studying work it is important to examine whether it is the force that causes displacement. It is only when the displacement is caused by the force that we can say the specific force has done work on the object.

Work is calculated by the following formula:

work  =  force  ×  displacement

When the unit of the force is Newton (N) and displacement is measured in metres (m), the unit of work is Newton metres; 1 Newton metre is equal to 1 Joule (J).

In ancient times people invented simple machines that helped them overcome resistive forces and were able to do work that seemed impossible, like building the pyramids in Egypt.

Simple machines work in the following ways:

• transfer a force from one place to another
• change the direction of a force
• increase the magnitude of a force
• increase the displacement the force causes
• change the speed of the force.

Examples of simple machines are the lever, the wheel and axle, the pulley, the inclined plane, the wedge and the screw.

A machine produces a mechanical advantage when the force applied by the person using it (input force) is smaller than the force applied to the task (output force).

Determine if the following example constitutes work:

A body builder lifts 100 kg above his head.

work

no work

Determine if the following example constitutes work:

A lady carries her shopping bags from the supermarket to her car.

work

no work

Determine if the following example constitutes work:

A father pushes a baby in a carriage.

work

no work

Calculate the work done in the following example:

An apple weighing 6 N falls from a branch, 3 m high up on a tree.

2 J

9 J

18 J

Calculate the work done in the following example:

A worker pushes a concrete block 5 m with a force of 20 N.

4 J

25 J

100 J

Calculate the work done in the following example:

A child pulls a toy 5 m with a force of 5 N.

1 J

10 J

25 J

What did ancient people invent in order to help them overcome resistive forces?

standard machines

senior machines

simple machines

Tick two different ways that a simple machine makes a task easier.

Changes the direction of a force.

Alters the power of people that perform the task.

Decreases the size of the task.

Changes the magnitude of a force.

Tick three simple machines from the examples below.

lever

plate

pulley

wedge

fork

Complete this sentence.

A machine is said to produce a mechanical advantage when the input force is smaller than the _________ force.

• Question 1

Determine if the following example constitutes work:

A body builder lifts 100 kg above his head.

work
EDDIE SAYS
This is an example of work. The body builder exerts a force on the mass of 100 kg and causes it to be displaced from the floor to above his head.
• Question 2

Determine if the following example constitutes work:

A lady carries her shopping bags from the supermarket to her car.

no work
EDDIE SAYS
This is not an example of work. The lady exerts a force on the shopping bags in order to lift them. However, the displacement is caused due to the lady walking to her car and not due to the force that caused the bags to be lifted.
• Question 3

Determine if the following example constitutes work:

A father pushes a baby in a carriage.

work
EDDIE SAYS
This is an example of work. The father exerts a force on the carriage, which causes it to be pushed along.
• Question 4

Calculate the work done in the following example:

An apple weighing 6 N falls from a branch, 3 m high up on a tree.

18 J
EDDIE SAYS
Work = force x displacement = 6 x 3 = 18 J.
• Question 5

Calculate the work done in the following example:

A worker pushes a concrete block 5 m with a force of 20 N.

100 J
EDDIE SAYS
Work = force x displacement = 20 x 5 = 100 J.
• Question 6

Calculate the work done in the following example:

A child pulls a toy 5 m with a force of 5 N.

25 J
EDDIE SAYS
Work = force x displacement = 5 x 5 = 25 J.
• Question 7

What did ancient people invent in order to help them overcome resistive forces?

simple machines
EDDIE SAYS
Ancient people invented simple machines in order to help them overcome resistive forces.
• Question 8

Tick two different ways that a simple machine makes a task easier.

Changes the direction of a force.
Changes the magnitude of a force.
EDDIE SAYS
Simple machines change the direction and magnitude of a force.
• Question 9

Tick three simple machines from the examples below.

lever
pulley
wedge
EDDIE SAYS
The correct answers are lever, pulley and wedge.
• Question 10

Complete this sentence.

A machine is said to produce a mechanical advantage when the input force is smaller than the _________ force.

output
EDDIE SAYS
A machine is said to produce a mechanical advantage when the input force is smaller than the output force.
---- OR ----

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