Super Strong

Want to demonstrate your super powers? Break a piece of string with your bare hands!

What you need:

A long piece of string of medium tensile strength. Don’t use very strong string, as you could cut your hand! Be careful.

What you do:

1. Wrap one end of the string around your left hand as shown in the picture. 2. With the other hand grasp the free end of the string 30 to 60 cm below your hand. 3. Wrap the string several times around your right hand.

4. Make a fist with each hand. Hold the fists together. Quickly pull your right fist down and push your left fist up.

5. The string should break inside your left fist at the point marked ‘X’.

Why does this happen?

This experiment demonstrates that ‘pressure’ is force divided by the area on which the force operates. One part of the string is as strong as any other part. The trick here is to make one part work against the other.

By looping the string, the force becomes concentrated on the small area where the string intersects or crosses itself. This increases the pressure, so that the string acts like a blade. It actually cuts through itself!

What do you learn?

You used technology to solve a problem. Machines are a technology that enable people to use a little force to move a very large load. There are six simple machines that are key to technology: the inclined plane, the screw, the wheel and axle, the pulley, the wedge and the lever. The lever is the earliest and simplest machine. Complicated machines are combinations of these six simple machines!