Concept Overview
- Newton's 3rd Law
- Acceleration is an inverse function of mass
Lecturer Procedure
Steps to Follow
- Demonstrate the ease of rolling the connected cars back and forth, showing they can coast with considerable freedom.
- Use scissors to cut string between the boxes.
Expected Result
Cars will travel in opposite directions; the less massive car will have the greater acceleration.
Historical References; Taken from original work of Percy H. Carr, 1970
“In lecture prepare the students by drawing a rough sketch on the board (since the details of spring and twine cannot be seen by them) and get them to realize that each cart must have the same force exerted on it; therefore, each should move. Tell them how you are going to carry out the experiment with no mention or hint of possible outcomes.”
“When the usual gasp of surprise and amazement has quieted, you can say something like the following. ‘I judge from your reaction that some of you, at least, have come to the conclusion that these carts are not alike. That is true; they are not alike. (Remove the can from the light one, -- empty. Remove the can from the other, -- a large black lump. Pick the lead out and set it down on the table with a resounding thump.) That is what we mean by mass. For a given force, the acceleration is inversely proportional to the mass.” The point is made. No more need be said."
Video Demonstration
There is no audio for this recording.