Conservation of momentum

Similarly, **B** will exert a
force on **A**, which will change **A**'s momentum. These
forces, by Newton's 3rd law, are equal and opposite, and therefore
the changes in **A**'s and **B**'s momentum are equal and
opposite:

In other words,

We now define the **total momentum** of the system as the sum of the
momentum of **A** and **B**. We then have

This says that the total momentum of a system is conserved. This principle,
together with energy conservation, has many far-reaching consequences
in many areas of science.

1999-09-29