Introduction

The Energy Story

  Energy Is Born
  Energy Types
  Energy Changes
  Energy Generation

The Energy Problem

  Conservation of Energy
  Aging of Energy
  Finite Resources
  The Oil "Crisis"
  Energy Pollution
  Discussion Topics

The Energy Solution

  Conserving Electricity
  Appliance Efficiency
  Heating Conservation
  Renewable Energy

Web Links

Teacher Guide

About the Author


Secret Lives Title - The Energy Story


agif - sking downhill
The Ten Types
Gravitational Energy

 

Gravitational energy is due to the force of gravity caused by the attraction of all other masses to the mass of the earth. As you lift an object to a higher elevation, you give that object increased gravitational energy. You can get that energy back (or most of it) when you drop the object and it falls to the earth's surface.

The amount of gravitational energy that an object possesses can be calculated from the equation:

where


 

GPE = gravitational potential energy
m = mass
g = acceleration of gravity
h = height above the ground (or a reference level)
The acceleration of gravity near the surface of the earth is constant, around 9.8 meters per second squared. Therefore the GPE is directly proportional to the mass and directly proportional to the height.

An example of a device that uses GPE is the pile driver. A huge cylinder of metal is raised and then dropped on wooden piles to drive them into the groud. Then there is the device that drops a metal object onto soda cans to flatten them so they are easier to store before disposal.

 

The most common use of GPE is in hydroelectric power plants that use the GPE of water to generate electricity. Nature convieniently evaporates water which then rains on ground that is at a higher eleveation. The water therefore possesses more GPE which can be released when the water is allowed to fall over a dam.

picture of dam