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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