MECHANICS - NEWTON'S FIRST LAW - MEASURING INERTIA NC State University Faculty Access

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Inertia Balance
# 1F10.11


Description: The inertia balance is designed for use in a laboratory experiment in which mass is quantitatively measured independent of the earth's gravitational force. This same method is used in determining the mass of an object under weightless conditions in space flights.
The apparatus consists of two small platforms connected by two horizontal, nonsagging, spring-steel blades. A cylinder with a shoulder on which it can rest in a hole in the platform and a hook by which it can be suspended are included. This cylinder may be used as an object of unknown mass.

Instructions: The apparatus is calibrated by determining the vibration frequency for several known platform loads, using the data obtained to plot a calibration curve. The vibration frequency of the balance is then determined with the unknown as the load and the mass of the unknown read from the calibration curve.

Securely clamp the inertia balance to a well-braced laboratory bench by means of a C-clamp. The platform with the hole should be used for supporting the load.

Use a stopwatch to determine the time for a given number of vibrations. Begin with a load of two 100 gram masses on the platform and determine the time for 100 vibrations. By using small amplitudes and waiting until several oscillations have occured before timing, there will be no slippage of the weights on the platform. Repeat, determining the time for 100 vibrations for loads of 3,4,5 and 6 weights.

Compute the period in seconds for each load and plot period against the weight of the corresponding load. Also, plot period squared against the corresponding load. Which curve is more nearly a straight line, and what conclusion can be drawn as to the relationship between mass and period?

Place the unknown mass in the hole of the platform and determine the period of the vibration. From the calibration curve, obtain the mass of the unknown and compare the value with that obtained by weighing the unknown on a balance.

Parts: Inertia balance
6-100 gram masses
Stopwatch

Purchased/Built: purchased

Setup Time: 1 hour

Quant. in Demo Room: 1

Source: Central Scientific

Demo References
Meiners 8-2.7 A horizontal leaf spring as an inertial balance.
The Video Encyclopedia of Physics Demonstrations Disc 08-24 Place masses on a platform supported by horizontal leaf springs.

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