MISCONCEPTION PREVENTION

Some people mistakenly believe that when particles become warmer that they become bigger...

do cold particles get bigger      when they heat up?

NO!

What happens is that when particles heat up, they MOVE MORE...


Imagine four particles flying around in this box...





 
If you heated them up,

They'd put more pressure on the container, and if the container is flexible, it will expand.  You can observe this phenomena with car tires that look too flat on a cold day, but look fine on a hot day. 
 Have you ever taken a sealed plastic pop bottle outside in winter?  As the temp goes down, the particles move less, and take up less space.   The air outside the bottle still exerts its normal pressure, and you can see and hear the bottle crinkle to a smaller size.  Try it in your freezer!