Why can't I breathe on rollercoasters?

You can't breathe on rollercoasters because of a fact of physics called G-Force. G-Force (Gravity Force) is a way of measuring pressure put on objects in motion, and is a result of inertia. Inertia is a property of matter, and is what makes objects resist change of direction and velocity. One good example is in a car. When you are going fast and slam on the breaks, your inertia is going to resist the decrease of speed, and push you forwards in your seat. This is the same in rollercoasters. When you are being wildly spun around and slung everywhere, your inertia is trying to resist all of the changes in velocity and direction. G-Force is a method of measuring how hard your inertia is. (G-Force 1 = one earth gravity.)