There’s no Such Thing as Gravity:
The World Just Sucks!

A slightly different approach to general relativity
for high school physics students

By Mark Sowers

Table of Contents

Chapter 2:
Potential Energy

Let’s say you have a really strong arm and are able to throw a 1kg rock from the ground, up through a window on the 7th floor of a building (about 74 feet up). You give it the energy it needs to reach that height (about 220 joules of kinetic energy in the form of vertical motion[1]).

There is a law of physics called the conservation of energy. It states that energy never just disappears. Energy is always there in one form or another. As that rock rises, it slows down. Its kinetic energy is converted into potential energy. And when it reaches 74 feet, all its kinetic energy is gone. Those 220 joules are now entirely in the form of potential energy.

Potential energy isn’t a very satisfying concept to most physics students. Potential energy is the amount of energy that an object would have if it were to fall from a given height. If our rock falls 74 feet, it would reach the ground with 220 joules of kinetic energy. But where did this energy come from? Does the force of gravity somehow transfer energy from the Earth into this rock? If so, does that mean that the Earth now has 220 joules less energy than it did before?

It depends on how you look at it. One way of looking at it says that the Earth does indeed have 220 joules less energy than before the rock fell. And while valid (meaning all the math works out), explaining how this happens starts to involve gravitational force-carrying particles (called gravitons) and becomes much more complicated than the scope of this paper.

Another way of looking at it says that the energy is somehow ‘stored’ in the rock, and is ‘released’ when it falls. But that leaves the question of just how that energy is stored, and how does it know to release when the rock is falling? It is this approach that I will focus on. To answer these questions we need to know something about energy itself. And when it comes to energy, there is one equation that says it all.

 

[1] Given the equation for potential energy (U) as U=mgh we find that 1kg(m) times 9.8m/s2(g) times 22.5m(h) gives us about 220 joules.