Motion of a ball in different reference frames: Testing Experiment

Aim

Test Newton's first law by using it to make a prediction about the motion of a ball from two different reference frames.

Prior Knowledge

1. Newton's Laws
2. Notions about circular motion

Description of the Experiment

This video shows the motion of a ball rolling on a rotating table from two different reference frames.

Mike, Dave and Aaron are sitting at a circular rotating table. They are rotating with the table. They roll the ball to each other across the table. Mike holds the camera to give a view of the motion of the ball in this reference frame.

A second camera is mounted above the rotating table and is fixed relative to the room. This gives the view from a second reference frame.

1. Use Newton's first law to make a prediction about the path that the ball will take as viewed from Mike's reference frame (rotating with the table.)
2. Use Newton's first law to make a prediction about the path that the ball will take as viewed from the camera that is fixed relative to the floor of the room.

Then go and test your predictions for the paths of the ball in the two different reference frames by watching the video.

Addtional Information

It is really difficult to plot the paths of the balls by just watching. A good method is to place a transparent plastic sheet over the screen, step the movie frame by frame and use a permanent marker to place a dot where the ball is each frame on the plastic sheet. See if the resulting paths match your predictions.

Not all throws are equally clear. Throws 2 and 4 give clear and unambiguous data.

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

Questions

Draw a picture representing the path of the ball as seen by different observers. Who are those different observers? Can you say what the real path is?