F and A for Fixed Mass - Activity

Introduction

Newton described in his First Law how an object behaves when balanced forces act on it, or when there are no forces at all. His Second Law describes what happens when an unbalanced force acts on it. This activity looks at half of the experimental evidence needed to arrive at Newton's Second Law.

Task 1: Acceleration for varying forces

1. Open the Yenka Model 1. Drag the force control for the cart until it reads 0.7 N. Describe the motion of the cart until it reaches the right-hand limit of the track.
   Answer

   Constant acceleration from rest to 0.375 ms​^​-1 in 5.2 s
2. Calculate the acceleration of the cart from the v-t graph. Check with the a-t graph. Do the answers match?
   Answer

   0.072 ms​^​-2
   yes.
3. Repeat for these other forces. Complete the following table, and plot the corresponding graph on paper.

   Unbalanced force on cart (N)	Acceleration (ms​​-2)
   0.7	Answer 0.072
   1.5	Answer 0.15
   2.2	Answer 0.22
   3	Answer 0.3

4. What happens to the slope of the v-t graph as the acceleration increases?
   Answer

   It increases.
5. Does the size of the mass vary between experiments?
   Answer

   No.
6. Describe the relationship between unbalanced force and acceleration for a constant mass.
   Answer

   Acceleration varies directly with unbalanced force.

Summary

This experiment shows a highly engineered system where precisely sized forces are applied over a distance by a control rod. This kind of arrangement is difficult to arrange but is used in applications like moving the control surfaces of aeroplanes or to guide sensitive medical instruments.