1. Stretching forces

2. What can forces do? A force is a push, pull or twist. Forces can change: the movement of an object the shape of an object Today, we will look at forces changing the shape of an object

3. Experiment: Stretching springs You are going to carry out an experiment where you stretch a metal spring You are looking for a relationship between the force stretching the spring & the length of the spring You are going to make a results table and plot a graph You are going to use your graph

4. Hang a spring from a support. Hang a one newton force (what mass is this?) on the bottom of the spring and use a ruler to measure the length of the spring. Record this in the table. Repeat this process until you have 5 newtons on the end of the spring Plot a graph of spring length against stretching force. Experiment: Stretching springs Force in newtons Spring length in mm 1 2 3 4 5

5. Drawing graphs 1.Draw two pencil lines. Each line is called an axis. Don’t draw them too close to the edge of the paper. 2.Label each line with the thing you are plotting. 3.Mark the numbers on the horizontal line. Each step should go up by the same amount e.g. go up in 1s or 5s or 10s. Do the same on the vertical line. 4.Mark the results as crosses (x). Use pencil to do this. 5.Use a ruler and a pencil to join up the crosses BUT ONLY IF YOU WILL GET A STRAIGHT LINE.

6. 3 Spring length in mm 20 241 40 60 80 100 Force in newtons 120 Force in newtons Spring length in mm 160 280 3100 4120 5140 5

7. Conclusion Complete this sentence: “As the force stretching the spring…” Is there a pattern to these results? Describe it if you think there is. How long was the spring with no stretching force? Use your graph to work out how long the spring would be if the stretching force was 2.5 newtons, 3.8 newtons & 4.9 newtons Use your graph to work out what stretching force is needed to make the spring 85 mm long. Without using your graph, can you predict how long the spring would be if the stretching force was 10 newtons? What about 100 newtons?

8. Question Sayam knows that forcemeters contain a metal spring. Can you explain why metal springs are used? Becky thinks that a forcemeter could be made with a rubber band. What do you think? How could you test if she is right?