Here's a breakdown:
At Rest:
* Force: The body exerts a force on the ground equal to its weight (mass x acceleration due to gravity). This is a static force.
* Momentum: The body is at rest, so its momentum is zero.
Dropped from a Height:
* Force: When the body falls and hits the ground, it experiences a rapid change in momentum, going from a downward velocity to zero in a very short time. This change in momentum results in a much larger force being exerted on the ground during the impact.
* Momentum: The body has a downward momentum before impact, and this momentum needs to be transferred to the ground, creating a larger force.
The Key Difference:
The difference lies in the impulse applied. Impulse is the change in momentum, and it's equal to the force multiplied by the time over which the force acts.
* At rest: Impulse is zero because there is no change in momentum.
* Dropped from a height: The impulse is significant because there is a large change in momentum in a short time.
Example: Imagine dropping a bouncy ball. When the ball hits the ground, it compresses, slowing down over a short time. This compression increases the time of impact, reducing the peak force exerted. If the ball were completely rigid and stopped instantly, the impact would be much harder.
In conclusion:
While the body's mass and acceleration are constant in both cases, the force exerted on the ground is significantly higher when the body is dropped from a height due to the sudden change in momentum (and the corresponding impulse) during the impact.
