Here's why a brick can be broken over a hand without causing pain:
* Force: The force exerted by the hammer on the brick is very large, but it acts over a short time interval.
* Time: The time it takes for the hammer to break the brick is very short. This means the impulse (change in momentum) is also very short.
* Momentum: The hammer and brick experience a change in momentum during the collision.
* Impulse: Impulse is the product of force and time. Since the time is short, the force required to break the brick is also large.
* Pressure: The force applied by the hammer is concentrated over a small area of the brick, creating high pressure. This pressure is what causes the brick to break.
* Hand: The teacher's hand experiences the same force as the brick, but over a much larger area. This distributes the pressure and reduces the impact.
In summary:
* The force applied to the brick is very large, but it acts over a short time.
* The pressure exerted on the brick is high enough to break it.
* The pressure exerted on the hand is much lower because the force is distributed over a larger area.
Safety Note: This is a dangerous demonstration that should only be performed by a trained professional. There is always a risk of injury, even when done correctly.
