Simple Science Experiment: Conservation of Momentum with Marbles - MetroFamily Magazine
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Simple Science Experiment: Conservation of Momentum with Marbles

by Steve Davala

Reading Time: 2 minutes 

Sir Isaac Newton did some great experiments with motion back in the day. He investigated gravity, inertia, acceleration, force and momentum, to name a few things. He purposed some laws of motion, and the third law of motion deals with momentum and that for every action there is an equal and opposite reaction. What? This month I will explain this law with several easy to do projects that will get your science thinking going. 

Materials: 

About 10 identical marbles.

A table with a pull out leaf or a large picture book or a gift wrap tube cut in half lengthwise.

The extra experiment will require two skateboards.

Procedure:

If you have a kitchen table with a leaf in it, pull the table open slightly to make a track for some marbles.

Place all but one of the marbles into the track (or put them onto the tube or book) and make sure they all touch each other.

Roll one marble directly into the line of marbles and see what happens!

Once you see this, make a prediction about rolling two or more at a time into the line of marbles and try it.

If you have any different size or weighted marbles, you can experiment with them.

Explanation:

Momentum is a property of moving things. It depends on an object’s mass and how fast it is moving. In a collision, according to Newton’s third law of motion, momentum is conserved. That means what goes in, has to come out. That is why when you hit one marble into the stack, only one moves out. Momentum is kept the same. Same with two marbles. Two in, two pop out. But did you experiment with bigger marbles? You’ll notice something strange when you do this. It is better explained with this next part of the experiment.

Another experiment: 

Set the two skateboards up right in line with each other (like two trains on a track).

Safety! Have two kids wear helmets.

Standing on the boards, the kids will face each other, hold their hands up to each other and one will push the other one away.

Experiment further: 

When one kid pushes, both kids move! Again, that is the “conservation of momentum.” If the two kids are the same size, they should move the same distance and speed (although the board bearings play a big part in this, too). But what about different-sized kids? Maybe your mom stepped onto the board with you? Momentum is still conserved even though the smaller kids moves faster away. Both people still have the same momentum, it just looks different. Check out the Steve Davala’s website to see more about the conservation of momentum. 

I hope you enjoyed these simple experiments. If you have more questions about this, or need tips about science fair ideas around this topic (or others), contact the author. 

Steve Davala is a high school chemistry and physics teacher who likes to write and work with Photoshop. He’s got two kids of his own and subjects them to these science activities as guinea pigs.                    

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