** Experiment 9:** Mr. Einstein drops his wife's favorite potted
plant while traveling at a high velocity. It shatters. Meanwhile, his wife
is standing in the field watching.

__Question__: What will they each observe?

__Answer__: They both agree that the pot shatters when it hits the
surface and that Mr. Einstein is in BIG trouble. However, from Mrs. Einstein's
point of view, Mr. Einstein's time slows down and she sees the plant fall
in slow motion. This raises the question of why the pot shatters if it seems
to gently float to the surface of Mr. Einstein's railroad car. The answer
has to do with momentum. Momentum is the amount of "punch" something
has. Physicists define momentum as the product of mass and velocity (momentum
= mass **x** velocity). For instance, a car hitting you at 1 mph will
do a lot more damage than a feather hitting you at 1 mph because it has
more "punch". This extra punch or momentum is a consequence of
the car's greater mass. Likewise, if both Mr. and Mrs. Einstein agree that
the dropped pot shatters, then this is because the momentum of the pot has
remained unchanged. However, since Mrs. Einstein sees the pot falling with
less velocity, this also means that **its mass must have increased**
in order for momentum to be conserved.

__Conclusion__: When an object goes fast with respect to us, not only
do we see its clocks slow down and its length shorten, we also see an increase
in its mass!