Goal: Perceiving the presence of forces from changes in position.
Source: UMPERG
Below is shown a strobe diagram indicating the position of four objects
at successive time intervals. The objects move from left to right.
![](/files/Item033_fig1.gif)
During the intervals shown, which of the objects experience no net force
in the horizontal direction?
- Object A only
- Object B only
- Object C only
- Object D only
- Objects A and B
- Objects B and C
- Objects A and C
- None of the above
- Cannot be determined
Commentary:
Answer
(8); Objects with no net horizontal force will move with constant velocity. The objects moving with constant velocity are B and D. This question helps to reinforce the idea that it is change in motion, not motion itself, that requires a force.