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Effects of Forces

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Core• State that a force may produce a

change in size and shape of a body.• Plot extension/load graphs and

describe the associated experimental procedure.

• Describe the ways in which a force may change the motion of a body.

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Plastic

If you put a force on an object making the object change shape and it stays the same shape after you remove the force we say the object is plastic.

Example?

Plasticene

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Elastic

If you put a force on an object making the object change shape and it returns to its original shape after you remove the force we say the object is elastic.

Example?

A spring

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Elastic and plastic

Elastic Plastic

Write down four examples of plastic and elastic materials.

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Match the force with its definition:

Tension

CompressionThe force on a material

when it is being stretched.

The force on a material when it is being

squashed.

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Tension or compression?

Your triceps muscle when you bend your arm.

A fishing line holding a fish.

A football being kicked.

A string holding a conker.

Pushing in a syringe.

An arrow in a bow.

Your biceps muscle when you bend your arm.

T – Tension C - Compression

T

T

T

T

T

T

T

C

C

C

C

C

C

C

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Standing on a plank:

Where is the plank being compressed?

Where is the plank being stretched?

What force pulls down on the man?

Tension Compression

Gravity

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KS4 Forces

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Forces and motion

If an object is stationary and an unbalanced force acts on it, it will start to move.

If an object is moving and an unbalanced force acts on it there are three possibilities…

The object could speed up.

The object could slow down.

The object could change direction.

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Supplement• Interpret extension/load graphs• State Hooke’s Law and recall and use

the expression F = k x• Recognise the significance of the

term ‘limit of proportionality’ for an extension/load graph

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Stretching springs

1. Attach a spring to a stand.

2. Record the length of the spring using a ruler.

3. Add a 50g mass to the spring.

4. Record the new length of the spring.

5. Continue to add masses to the spring up to 500g in total.

6. Plot a graph of load against extension.

7. What do your results tell you?

What do you predict will happen as masses are attached to a spring?

Mass (g)

Load(N)

Length(cm)

Extension(cm)

0 0 2.4 0

50 0.5

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Load and extension for a metal spring

Load (N)

Extension (cm)

Where is load proportional to extension?Where the graph is a straight line.

Load extension

Elastic limit

Plastic region

What do we call the point after which the spring will not return to its original shape?

The Elastic Limit