What makes an object move?

Lesson Questions

  • What makes an object start moving?
  • What changes how an object moves?

From our everyday experiences, we know that sometimes objects are at rest (not moving), sometimes they are moving, and sometimes the way they are moving changes (speeds up, slows down, changes direction).

We can represent an object’s speed in one direction using a speed-time graph, as shown in the figure below.

The image displays a postition-time graph, with position on the vertical axis and time on the horizontal axis, and a speed-time graph, with the speed on the vertical axis and time on the horizontal axis.
A distance-time graph shows an object’s position at a given time, and a speed-time graph shows an object’s speed at a given time.
Make a prediction

In the movie below, a cart is given a push on a track with very low friction. Sketch your prediction for the general shape of the speed-time graph for the motion shown: the cart is given a push, moves along the track, and is caught at the other end of the track.


motion detector is a device that can measure an object’s position using sound (like how a bat uses echolocation). A computer can use those measurements to create a graph of position or velocity versus time.

Watch the movie below where a speed-time graph created by a motion detector is shown along with the cart’s motion.

Compare this graph to your prediction. In what ways are they similar? In what ways are they different?


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