Thursday, July 15, 2010

Action/Reaction: Car on Marbles

Here's a little activity/demonstration that shows that when a car drives, it pushes on the ground and the ground pushes on it. 

Place a handful of marbles on a cookie sheet. 

Place a piece of cardboard (box board or corrugated, either works) on top of the marbles.

Then you need self-propelled toy car or truck.  Wind up the vehicle and hold the wheels (so it doesn't go yet).  Place the car on the cardboard and let go.

The car will move forward and the cardboard will move backward. 

The ground (cardboard) pushes on the car, and pushes it forward.  The car pushes on the ground (cardboard), and pushes it backward. 

In the real world, we aren't able to see the car pushing on the ground, because the ground is part of the Earth and is SO much more massive than the car that it doesn't move. 

This activity is good for demonstrating the usually invisible forces at work when a vehicle moves.  You could use it as a demonstration or as one station in a series of 3rd law activities.

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