# Hit to the ground

What happens if an object –may be a watch or a telephone-
falls down and hits the ground?

It is possible to __estimate__ the enormous acceleration
with nearly no equipment, but a little bit of calculation.

It is interesting to learn about these high accelerations
that happens day after day in our life.

Very interesting for physics is, how to estimate.

May be, we only teach to find exact solutions. In science it
is useful to estimate and to know something about the quality of the
estimation.

## What we need

-one ball of “Play Dough”,

-one ruler 1m

-one small ruler

## The idea / definitions

Let the ball with the diameter D fall down on the table.

The diameter d of the circle that deforms the ball contains
information about the __average__ acceleration.

Attention! To important words: __average__ and __estimation__.

-H: height before the fall, measured between table and lower
edge of the ball

-h: see the sketch

If d<<D, then D is (nearly) the same before and after
the crash with the table.

## Velocity of the “first touch”

_{}, simple but not exact for the following calculation.

The ball falls through the distance H+h, and these energy
works in the deformation.

If the ball is not very small and not very soft, the mistake
may be irrelevant.

But it is always important to think about it.

**brake**

_{}

__h-calculation__

_{}

__example__

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