Inertial Balance

WHAT TO DO:

  • With no mass on the balance, start the balance swinging by pulling it to the side about 1 inch.
  • Watch the oscillation (back and forth motion) of the balance.
  • Place the disk mass onto the post on the balance.
  • Again, start the balance swinging by pulling it to the side about 1 inch.
  • Watch the new oscillation of the balance.

How does the oscillation change when you change the mass placed on the balance?

ANSWER: With less mass on the balance, it oscillates faster. 

WHY:  When the balance has extra mass, it oscillates slower because it has more resistance to motion. We call this tendency of an object to resist any change in its motion inertia. The more massive an object is, the less easily its motion can be changed. Newton’s 1st Law is sometimes called the Law of Inertia, since it describes this property.

Newton’s 1st Law:

An object at rest will stay at rest and an object in motion will stay in motion unless acted on by some unbalanced force.

So, the inertia of an object is measured by finding its mass. If you were to time the period of the inertial balance with several different known masses, you would be able to determine the relationship between period and mass. Then you could figure out the mass of an unknown object just by observing the period of the inertial balance. This method would find the same mass for the object at the Mass Scale exhibit!

 

Physics Lecture Demonstration Database