Video: Watch this demo
Description: This demonstration shows that Simple Harmonic Motion (SHM) looks like the 2-D projection of circular motion.
- Circular motion peg apparatus
- Variable rheostat
- Large golden spring
- Set of masses
- Slide projector
- 3 banana plug cables
- Large metal rod
- Small metal rod with hole at the end
- Table clamp
- Small stool
- Attach the rods to the table. Have it so the spring hangs over the end of the table.
- Attach the spring to the hole in the small rod, and attach a mass to the end (around 200-500g).
- Place the rotating peg apparatus next to the spring.
- Adjust the height of the spring so that the equilibrium position of the spring is at the center of the peg’s height.
- Connect the rotating peg apparatus to the variac. Connect the three cables to the variable rheostat. Use a red cable on both sides, and a black cable connected to the black terminal on the rheostat.
- Set the variac to about 80V and turn it on.
- Make sure moving the rheostat to the faster side actually speeds up the motor. If it doesn’t, reverse the red cables.
- Adjust the speed on both the variac and rheostat to match the frequency of the spring.
- When in the class, put the slide projector on a small stool and prop it up with a book to project both the spring and peg onto a screen.
- Turn on the slide projector.
- Turn on the variac. Explain that this peg is moving in a circle, but the 2-D projection makes it look like SHM.
- Pull the mass on the spring down to be level with the bottom of the rotating disc and let it go when the peg comes around.
- Slight adjustments may be needed on the rheostat to match the two oscillations. (It can be hard to time well but should illustrate the concept)
- When finished, turn off the variac and slide projector.
Note: This demo is hard to setup and hard to operate.