Balancing on knives
How can you build bridges with just knives – no nails or ropes?
Observe caution when working with knives.
- three butter knives;
- three thin wooden sticks;
- three paper cups.
Arrange the cups to form a triangle. Set the handle of each knife on the base of a separate cup and interweave the blades so they overlap with one another. You can even balance a heavy glass of water in the center, where all three blades are connected – the construction can support it! Repeat this experiment with thin wooden sticks. The construction still holds!
The whole system remains balanced because the pivot points of its various components combine to support each other. Each knife rests with one end on a cup, and the opposite end on another blade. In other words, for each knife there are two others; the force from the first is directed upwards, and the force from the second is directed downwards. Therefore, movement in any direction from any of the knives sets the entire system in motion. The forces are arranged in such a way that if the pressure on one knife increases, the others tend to compensate. The same goes for the thin wooden sticks.