1G30.20 Mass on a Spring on a Balance

A large mass on a stretched spring is tared on a pan balance. The string is burned and the motion observed.

A repurposed pan balance has a large copper bucket on the left side and a metal plate on the right. A table stand behind the pan balance supports a hanging spring, such that the spring hangs over the center of the pan balance. A 1-kg hooked mass hangs from the spring. A piece of cotton twine is tied to the bottom of the hooked mass and fastened to the metal plate with a recycled hard drive magnet. The string is pulled tight enough to extend the spring while leaving the mass hanging a few inches above the balance. A propane torch in the foreground suggests that the flammable cotton string is not long for this world.

The set up for the demonstration. You will need 3.5 kg to put in bucket to balance.

A close-up side view of the pan balance, clearly showing the hard drive magnet anchoring the cotton twine to the balance's metal plate. The 1-kg mass hangs a few inches above the pan balance. A second hard drive magnet, a cone of twine, and a propane torch appear in the foreground.

How to attach string to platform.

Observe balance begin to oscillate.

Location: pendulum clamp FG-6, rod stand (aisle F), metal sheet for platform F3-4, spring F4-3, masses FG-7, pan balance with bucket G2-5, string DE-4, propane torch (workroom)