Rubber stopper versus cork stopper (1/2 mass).
In the first part of this demo, we are compressing air into the bottle and popping out the rubber cork. The cart goes the opposite direction of the rubber cork. This shows an equal and opposite reaction. The second video on the right, does basically the same thing. But this time it has 1/2 the mass of the rubber cork. When it pops, the reaction on the cart is visibly less than the previous video. So the greater the mass, the greater the reaction on the cart or the less the mass of the cork, the weaker the reaction forces on the cart. Because the cork of the second video has less mass, it pops out at a greater velocity than the first cork. This can be shown by moving aside the cork catcher and allowing it to strike on the floor. There is about 1.5 meters difference between the landing sites of both the corks involved.
This demo is easy to reset, can be demonstrated over and over again, and is very safe. It would be great to use in a science museum. Kids would love it.
One last thing, I have a third video not posted yet, where the rubber cork has a very small hole in it. It doesn’t pop, but slowly moves the cart down the track. This presents a good question for students to answer, why does it move at all, if no actual mass is popped away? Is it the mass of the air molecules ejected and it’s reaction to the air molecules around it that makes it move? What if we placed a board in the path of that air stream, would it push away with greater force the closer one brings the board to the cork?