Materials Required:
l Heavy cord
l Rock, weighing several kilograms but easy for you to lift
l 2 pieces of light string
l Tree
Procedure:
- Tie a piece of heavy cord around the middle of the rock.
- Tie a piece of light string to the cord (the string should be just strong enough to support the rock’s weight), and suspend the rock from a low tree branch or swing set.
- Tie another piece of string to the opposite side of the cord, underneath the rock, and let this piece hang freely.
- Give the bottom string a rapid tug. The string will snap, leaving the rock in place.
- Pull the remaining piece of this lower strand with a slow, steady motion. The top string will break, causing the rock to fall.
This Is What Happens:
An object at rest tends to remain at rest. This is basic law of science and is called inertia. The force of your rapid tug did not reach the upper string because of the rock’s inertia—that is, its tendency to remain in place. However, when you applied a steady force, you were able to move the rock slightly. The top string received this force, in addition to the rock’s weight, and the string broke.
