# Force and extension

Investigate the relationship between force and extension of a spring.

### Method

1. Set up apparatus as shown in the diagram. Secure the metre rule and ensure that it is vertical. Consider using the protractor to check that it is at 90 degrees.

2. Attach the mass hanger s -hook and pointer to the lower end of the spring. The pointer should just touch the metre rule.

3. Read the pointer value from the metre rule. Record this length in a suitable table. This is the initial length of the spring for zero mass. We can neglect the mass of the hanger.

4. Add a 100g slotted mass to the hanger. Record the mass in kg in the table.

5. Read the new position of the pointer on metre rule. This is the stretched length of the spring. Record this length in the table.

6. Calculate the stretching force = weight of masses: W = mg.

7. Calculate: extension = stretched length – original length.

8. Repeat the procedure by adding 100g masses in steps of 100g up to 1200g. Record the new stretched length each time by reading the position of the pointer on the metre rule. Subtract the original length from the new stretched length to calculate each extension.

 Mass/kg Stretching force/N = m x g Stretched Length/cm Extension/ cm = Stretched length – Original length 0.1 0.2 0.3 0.4

### Graph

Plot a graph of stretching force, F in N on the y-axis, against extension, e in cm on the x-axis.

Join the points with a line of best fit.