Concepts

Driven oscillator

Overview

A wheeled cart with springs attached is driven by a motor that is controlled by a variac. Magnets on the cart damp its motion. A motion detector connected to a computer helps graph the cart's motion.

Details

Equipment

• [1] Variac
• [1] DC motor
• [1] Cart with motion detector plate
• [1] Track
• [2] Spring
• [4] Small magnet
• [1] Motion detector with post attached
• [1] USB A-B cable
• [1] Lab stand
• [1] 90-degree clamp
• [1] Computer with Logger Pro (Windows or Mac OS)

Classroom Assembly

1. Connect a DC motor to the variac and position the motor such that students can see the rotation of the motor clearly.
2. Add as many damping magnets to the cart bottoms as desired.
3. Start with voltage at zero volts to begin.
4. Start up the computer.
5. Attach the cart to the plate.
6. Hook the springs to the cart and the track.
7. Mount the motion detector to the lab stand and position it to view straight down the track.
8. Connect the computer to the motion detector using the USB cable.
9. Start Logger Pro and make sure that the detector captures the cart's full range of motion.

Important Notes

• Increase the voltage carefully, be sure not to apply a voltage larger than 100 volts.
• If cart oscillations are too strong, add more magnets to the undersides of the carts.
• Knowledge of Logger Pro is essential.
• If the graph of cart motion clips at the high or low ends, try raising the motion detector or removing objects near the track.

Script

1. Connect the springs and the cart as shown on the image, if they are not already connected.
2. Attach the spring to a screw at the end of the track.
3. Connect the spring to a motor by a string.
4. Turn on the variac and slowly increase the voltage.
5. Put a 250g mass on top of the cart to increase the mass of the cart if necessary. Note that the mass of the cart is approximately 250g.
6. Start the data collection.
7. Go to a different page in the Logger Pro file for other measurements.

Additional Resources