# Experiments With Newton's Laws of Motion

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Newton's laws of motion are the law of inertia (first); the law of acceleration (second); and the law of interaction (third). They can be stated as: objects at rest (in motion) tend to stay at rest (in motion); force = mass times acceleration; and for each action, there is an equal and opposite reaction.

## Experiment for First Law

• Drop a tennis ball lightly onto carbon paper, marking blank paper underneath. Then hurl the tennis ball at the carbon paper. The latter makes a larger mark because its inertia keeps it in motion.

## Experiment for Second Law

• A student can drop blobs of Play-Doh or other amorphous adhesive onto a record rotating on a phonograph. The angular velocity will noticeably drop (especially if the turntable is off) because, by F=ma, the radial force applied to the record is still the same but the mass has increased, causing the angular acceleration to drop.

## Experiment for Third - No. 1

• Newton's Cradle is a set of strung marbles hanging as pendulums in contact. If some of them are raised, and allowed to drop down into the marbles at rest, the same number of marbles will be propelled off the other side. Though the exact behavior is dictated by the conservation of momentum and energy, the equality of incoming and outgoing marbles also demonstrates the third law.

## Experiment for Third - No. 2

• A seated child can kick his legs out to propel himself and his chair backward. This is the same principle as a rocket in space that can accelerate even without an atmosphere to push off (like an airplane requires).

## Experiment for Third - No. 3

• Attach equal weights with a string and hang them off opposite sides of a table, with spring scales inserted between mass and string to measure the opposing force each weight experiences. The equality of the readings demonstrates the third law. The equality will hold for unequal weights as well.

## References

• Fundamentals of Physics; Halliday and Resnick; Wiley: New York; 1989
• Photo Credit "Brighthawk Video Rocket" is Copyrighted by Flickr user: jurvetson (Steve Jurvetson) under the Creative Commons Attribution license.
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