1. Stretching springs and Hooke’s Law
Learning Outcomes:
Describe what is meant when an object is elastic
Describe how to measure extension of a stretched object
Accurately remember and use F = k x e
Explain what is meant by ‘the limit of proportionality’

3. Elastic materials
An object is elastic if it returns to its original shape
when the forces deforming it have been removed.

4. Non elastic materials
A polythene bag does not return to its original
shape when stretched.
It remains inelastically deformed .

5. Damping
A car has lots of springs.
Without dampers (shock absorbers)
the car would be too bouncy
and be unsafe!

6. Extension of specimen = present length – original length

7. Hooke’s law
provided the elastic limit
has not been exceeded.

8. Hooke’s law (Spring stretches in a non linear way beyond ‘P’) ‘P’
provided the
has not been exceeded.
proportional limit

9. Hooke’s law (Spring stretches in a non linear way beyond ‘P’) ‘P’
provided the elastic limit
has not been exceeded.
proportional limit

10. Q.1

11. Q.1

12. Q.2

13. Q.2

14. Experiment to investigate Hooke’s Law

15. Experiment to investigate Hooke’s Law
Load /N
Original length /mm
Final length /mm
Extension /mm 20 20 1 20 40 20 2 20 3 20 4 20 5 20
Force /N
Extension /mm

16. Experiment to investigate Hooke’s Law
Load /N
Original length /mm
Final length /mm
Extension /mm 20 20 1 20 40 20 2 20 60 40 3 20 80 60 4 20
100 80 5 20
120
100
Force /N
Extension /mm

17. Experiment to investigate Hooke’s Law
Load /N
Original length /mm
Final length /mm
Extension /mm 20 20 1 20 40 20 2 20 60 40 3 20 80 60 4 20
100 80 5 20
120
100
Force /N
These are sample plots !
Extension /mm

18. Conclusions:
The graph shows……….. 1. 2.
The anomalous results could be caused by………… 3.
The investigation could be improved by ……………

19. Conclusions:
The graph shows……….. 1.
the extension increases in direct proportion to the force 2.
The anomalous results could be caused by………… 3.
The investigation could be improved by ……………

20. Conclusions:
The graph shows……….. 1.
the extension increases in direct proportion to the force
because the straight line passes through the origin. 2.
The anomalous results could be caused by………… 3.
The investigation could be improved by ……………

21. Conclusions:
The graph shows……….. 1.
the extension increases in direct proportion to the force
because the straight line passes through the origin. 2.
The anomalous results could be caused by…………
A parallax error in taking the reading from the scale.
The spring moved on its support 3.
The investigation could be improved by ……………

22. Conclusions:
The graph shows……….. 1.
the extension increases in direct proportion to the force
because the straight line passes through the origin. 2.
The anomalous results could be caused by…………
A parallax error in taking the reading from the scale.
The spring moved on its support 3.
The investigation could be improved by ……………
Repeating the readings ( eg unloading), and calculating the average.
Increasing the range to see where Hooke’s law no longer applies.

23. Experiment to investigate Hooke’s Law A* work
The spring constant (spring stiffness) is the gradient of a force extension graph :
K = Δ F = N = N / mm
Δ e mm
= N / m
Load /N
Original length /mm
Final length /mm
Extension /mm 20 20 1 20 40 20 2 20 60 40 3 20 80 60 4 20
100 80 5 20
120
100
Force /N
These are sample plots !
5.8 N.
Extension /mm
82 mm