Target Period

Challenge: To design gravitationally powered rotating device that will achieve a target period and frequency.

Parameters: It must fit in your locker when not in operation. It can use up to one kilogram as the source of gravitational energy. The rotation must be horizontal with a diameter of between 10 and 25 cm and should be as constant speed as possible. It must have a 2.0 cm diameter white card on the outside of the rotating portion to aid in frequency/period measurement. It must be adjustable from 5.00 Hz to 10.00 Hz. (T = 0.200 s to 0.100 s)

Scoring: Mr. J will give your group the desired period, and you will have up to one minute to set up your device and get it going. At your instruction, Mr. J will measure your device for 5 seconds to find your result. Your score will be based on how close you get to the desired period by finding the absolute value of the difference.

difference = | measured period - target period |

Rank will be based on score, with lowest score earning highest rank.

Physics: The description of the dynamics of centripetal acceleration is necessary for the complete model of your device, and for understanding how you can adjust it to obtain a desired period of revolution. You can adjust tension and drag, length of string, mass of falling or rotating parts, angles, radii, etc. etc. etc.

Extensions: The mathematical relationship between any variable and the period of revolution can be calculated as long as the other variables are known and held constant. The forces may be difficult to measure, but can be assumed to be balanced in all directions except the centripetal direction if the device is rotating at a constant speed.

Help/Hints: Limit your variables if possible. The one you choose to vary should be able to change the period slightly more than required for the competition. Calibration of your device is essential so you can reliably make adjustments during the competition. Graph your calibration data and experimental results and draw a line of best fit. Use the equation of the fit line to find make your adjustment once you are given the target period.

Quiz Topics: Circular Motion

Newton’s Laws

Universal Law of Gravitation

Online Text: chapter 6

Timeline: Day 1 Planning, Day 2 Building, Day 3 Building, Day 4 Calibrating, Day 5 Contest