Hooke's law describes the relationship between force and extension in springs, stating that extension is proportional to the applied force until the elastic limit is reached. An experiment is proposed to measure and analyze how different materials react to applied forces, specifically observing elastic and plastic behaviors. Key findings include that materials obey Hooke's law up to their elastic limits, beyond which they undergo permanent deformation.

1. Hooke’s Law
 Hooke's Law gives
the relationship
between the force
applied to an
unstretched spring
and the amount the
spring is stretched.

2.  Recall: How does a spring
stretch when a force is applied
to it?
 Try stretching a piece of thin
copper wire and an elastic.
 How do they differ from the
springs?
 What does it feel like as you
pull harder and harder?
 Can you sketch a graph to
show how the force affects the
extension.
How different materials behave

3. Elastic and wire
 Different materials
react differently when
a force is applied to
them.

4. How does a spring behave?
 Aim: We shall conduct an experiment to
determine how the extension of a spring varies
with the stretching force.
 A spring is hung vertically from a fixed point and
a force is applied in stages by hanging weights
from the spring.

5. Extension = present length – original length
 Diagram
 The apparatus is set
up as shown. For the
purposes of this
experiment we shall
be using loads of
100g, and the
extension of the
spring shall be
measured in metres.

6. Method:
What is the independent
variable? (range?)
What is the dependent
variable? ( How will
this be measured
accurately?)
What are the control
variables?
Table:
single spring
Equilibrium
length
__________m
Total
Hangi
ng
Mass
(g)
Total
Hangi
ng
Mass
(kg)
Total force (mg)
g= 10 N/kg
Stretched length
(m)
Extension (m)
100
200
300
400
500
600
700
800
900
1000
1600

7.  Graph: Plot a graph of force
against extension.
 Conclusion:
 Comment on the shape of the
best fit line, try to describe the
pattern which appears. Have
you found any simple rule for
springs?
 What happened to the stretch
when you doubled the load?
And three times?
 Can you work out the
gradient? What does this
gradient mean?
 What happens when large
loads are added to the spring?
 How would the plot look if you
replaced the spring with a
stiffer spring? weaker spring?
Force (N)
Extension (m)

8. Hooke’s Law
 "Hooke's Law" is about
stretching springs and wires.
 Hooke's Law states:- the
extension is proportional to the
force
 the spring will go back to its
original length when the force is
removed
 so long as we don't exceed the
elastic limit.

9. Elastic Limit
 Below the elastic limit, we
say that the spring is showing
"elastic behaviour": the
extension is proportional to the
force, and it'll go back to it's
original length when we
remove the force.
 Beyond the elastic limit, we
say that it shows "plastic
behaviour". This means that
when a force is applied to
deform the shape, it stays
deformed when the force is
removed.
Elastic limit
Elasticbehaviour
Plastic
behaviour

10. Repeat the experiment using an
elastic
 What do you
notice?
 Does an elastic
obey Hooke’s
Law?

11. Class Experiment – Stretching a
wire – Vernier Scale
 Two wires of the same
material are suspended
side by side from the
same support. The main
scale is kept taut by the
weight L. The extension
of the wire for different
loads is obtained from
the vernier.

12. Elastic and wire
 Different materials react
differently when a force is
applied to them.
 If a material obeys Hooke's
Law, its extension is
proportional to the applied
force. If the force is removed,
the material returns to its
original length.
 Springs and metal wire obey
Hooke's law up to the elastic
limit. Beyond this point, they
are permanently deformed.
They will not return to its
original length when the force
is removed.
copper
rubberF
F
e
e

13. HysteresisrubberF
 What do you notice about
the plot when you load
and unload an elastic?
 What does the area
under a graph represent?
 ENERGY!!!
 See for yourself!! – Take
an elastic and repeatedly
stretch the elastic while it
is in contact with your top
lip.
 What do you notice?
 How could this energy be
measured from the
graph?