# Investigation based on Hooke's law.

Background Information.

This investigation will be based on Hooke’s law. Robert Hooke was born in 1635, he was well known for his studies of elasticity. Hooke’s most important discovery is the correct formulation of the theory of elasticity. An object is said to behave elastically when equal increases in the force applied to it produce equal changes in length. If a graph is drawn to show the average extension plotted against the load in Newtons a positive straight-line gradient should be seen, as extension is directly proportional to the load. The ratio between the load and the extension gives us a constant, this constant is called the spring or force constant.

Hooke’s law states:  F = kx

k = the constant of proportionality (the spring constant).

x =  the spring extension (e.g. x metres)

Or:

The deformation of a material is proportional to the force applied to it provided the elastic limit is not exceeded.

The elastic limit is when the spring is permanently stretched on deformed, so it doesn’t return to its original shape, as the molecules in the metal of the spring cannot return to the original shape; as the following graph demonstrates.

Elasticity can also be shown in this simple diagram:

The Molecular Level Description.

Before.

After.

Combinations of springs.

Hypothesis.

1) I think that the stretch of the two springs in series will be double the stretch of a single spring.

2) I think that the stretch of the two springs in parallel will be half the stretch of a single spring.

Therefore if x were to be the single spring:

1) The springs in parallel would be ½ x

2) The springs in series would be 2x

Plan.

Apparatus List.

2 springs

Meter ruler

Mass Hanger, 1 Newton

Mass disks, 1 Newton each

Clamp stand

Pencil, with grooves cut into it

Pointer

Single Spring.

1.Set the apparatus as shown in the diagram.

2) Check that the pointer, pencil, is at 90o from the spring to the ruler.

3) Hang the mass hanger on to the spring.

4) Record the extension of the spring against the ruler.

5) Add a Newton weight on to the mass hanger.

6) Record the extension of the spring against the ruler.

7) Repeat this procedure until 6 Newtons have been placed on the mass hanger.

8) Remove a Newton weight.

9) Record the extension of the spring against the ruler.

10) Repeat this procedure, removing all the Newton weights until only the mass hanger is left.

11) Add a Newton weight on to the mass hanger.

12) Record the extension of the spring against the ruler.

13) Repeat this procedure until 6 Newtons have been placed on the mass hanger.

Series springs.

1.Set the apparatus as shown in the diagram.

2) Check that the pointer, pencil, is at 90o from the springs to the ruler.

3) Hang the mass hanger on to the springs

4) Record the extension of the springs against the ruler.

5) Add a Newton weight on to the ...