Background+reading

Inertial Balance Readings:

"Mass: The quantity of matter in a body. More specifically, it is a measure of the inertia or "laziness" that a body exhibits in response to any effort made to start it, stop it, or change in any way its state of motion."2 Scientists measure things. A scientific question to ask is, "This definition of mass is very nice, but how can mass be measured?" There are several ways to measure mass - a triple-beam balance measures mass, for instance. The triple-beam balance has a couple of disadvantages, however. First, it is difficult to see how the measurement you make on a balance correlates to the definition of mass given above, and the triple-beam balance won't work where there is no gravity. If mass measures the "laziness" of an object in response to efforts made to change its velocity, it makes sense that you should be able to measure mass by making an effort to change the velocity of an object and recording its "laziness." This is what an inertial balance does. It uses two strips of spring steel to apply the same "effort" in order to vibrate it back and forth. (A vibration involves speeding up, slowing down, and changing direction, so the state of motion of the object is certainly changed.) If the object vibrates quickly it is not "lazy" - it does not have much mass. Objects that vibrate slowly have a large mass. By measuring how fast known masses vibrate on the inertial balance, you can construct a graph that "calibrates" the balance - that is, if you know how quickly an unknown mass vibrates you can use the graph to determine its mass. C:\Documents and Settings\Owner\Desktop\research for writing project\Inertial Balance - bhs physics.mht

**A:** An inertial balance is a mechanical spring device that moves an object back and forth in a regular oscillation in order to measure the object's mass. As the object oscillates on the inertial balance, it is constantly undergoing changes in its state of motion as the forces of the springs act on it. The greater the mass of the object, the harder it is for the springs to move the object back and forth. Consequently, the time it takes for one complete oscillation, the period, is large for a large mass and small for a small mass. Newton's first law of motion may be paraphrased as //Every object continues in a state of rest, or of uniform motion in a straight line, unless compelled to change that state by forces acting on it.// The property of matter that causes objects to resist changes in motion is known as //inertia//, which comes from the Latin word for sluggish or inactive. Because of this, the first law is also known as the law of inertia. You experience the effect of inertia whenever you try to set an object in motion. Think of trying to put a bowling ball into motion. You feel its resistance to motion when you try to move it. The quantitative measure of inertia is called //mass//. Thus, the property measured with an inertial balance is mass. Sometimes we specifically refer to it as the inertial mass to distinguish from gravitational mass, which is measured when we weigh an object on a conventional device such as a bathroom scale. When you step on a bathroom scale, the quantity measured is actually your weight, a force of gravitational attraction to the Earth that is proportional to your mass. The uniqueness of an inertial balance is that it can be used to measure mass independently of the weight. For example, an astronaut orbiting the Earth in the space shuttle appears to be weightless as the spacecraft and all its contents are in free fall. However, the astronaut's mass can be measured using an inertial balance fixed to the spacecraft. **Professor Edwin Jones**Department of Physics and Astronomy, University ofSouth CarolinaColumbia,SC
 * Q: How does the inertial balance relate to Newton's first law? **