### Re: How much force is there behind a bullet?

Date: Fri Jul 13 10:27:03 2001
Posted By: Nauzad Tantra, Undergraduate, Production/ Industrial engg., D J Sanghvi college of engg.
Area of science: Physics
ID: 994867596.Ph
Message:
```
Hi Andrew,
There is a law in Physics which says that the momentum of a system always
remains the same. It could be explained as follows.

Suppose a billiard ball is hit towards the other balls. The ball will have
some momentum (momentum = mass * velocity). When it strikes the target it
will transfer some of its momentum to the target, (the target being the
other ball). Accordingly only the target ball, or both of them will move
along the table.

However when a bullet is shot, things change a little. In the earlier case
we notice that both the balls are very hard in nature and one ball cannot
penetrate the surface of the other ball. A bullet is made such that it can
easily penetrate the skin and slice through it. In such cases the momentum
lost by the bullet may be very small (in which case the bullet will come
out of the rear of the persons body).

However if the bullet hits something impenetrable like a big bone, or if
the speed of the bullet is very very large, or maybe it is big in size
(big mass) then the chances are that the person will move backwards.

In simple terms a person will move backwards (or fly :) ) if the bullet
transmits momentum which is high enough to move the person. Lets take an
example.

Say the bullet is 100 gms in weight and travelling at the speed of 600
m/s (Thats nearly twice the speed of sound). If the person standing in its
path weighs about 60 kg. and the bullet stops inside his body, then he
would move backwards by a velocity of about 1 m/s. However if there was a
kid in the path (20 kg in weight), and the bullet transmitted its full
force onto him, then he would move at the speed of 3 m/s (which would make
him "fly" back).

free to write back to MadSci.

```

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