Activity #1: Racing Slinkys

In this activity, inertia, gravity, potential energy, kinetic energy, and longitudinal waves are demonstrated when the Slinky "walks" down stairs or an incline.

1. Show the class two Slinkys of different sizes and ask which one they think will win a race down stairs or an incline. (Graduated stacks of books work well; also any board or table top with a non-slip surface will do. Slope surface so rise equals about 1 foot for every 4-foot length.)

2. Place both Slinkys on the top stair or top of a ramp. Ask why the Slinkys remain motionless. What will it take to get them in motion? (Newton’s first law of motion: A body at rest will remain at rest unless an external force acts upon it. A body in motion will remain in motion in a straight line at a steady speed unless an external force acts upon it.)

3. Grip a coil of each Slinky at the top and flip it over toward the middle of the next lower step, releasing your hold (with this action, potential energy is converted to kinetic energy). The Slinkys race downward all by themselves.

4. After the race, ask why the smaller Slinky won. (As the Slinky moves down the steps, energy is transferred along its length in a longitudinal or compressional wave which resembles a sound wave that travels through a substance by transferring a pulse of energy to the next molecule. How quickly the wave moves through the Slinky depends on the tension and mass of the coil. The smaller the mass, the tighter the tension; the tighter the tension, the faster the wave speed. So, the wave moves faster through the smaller Slinky.)

Activity No. 1 provided by the engineers of ConocoPhillips.



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Last Updated: 02/16/03
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