6th Grade Science / Lesson 10 - Energy Created & Destroyed
Energy Created & Destroyed
What will we be learning today?
Can Energy Be Created or Destroyed?
The bicycle rider in the photograph stores energy in her body by eating foods. Then she changes this energy into kinetic energy by pedaling her bicycle to move it forward. As she rides across the countryside, she gains potential energy as she climbs hills. As she coasts down hills, her potential energy is changed back into kinetic energy, and she speeds up. When she stops, friction between the brake pads and the wheels slows the bike. The pads and the wheels get slightly warmer, and soon this heat escapes into the air.
The bicycle rider illustrates many changes of energy from one form to another. Yet, despite all of these changes, scientists believe that the total amount of energy in the universe remains constant. Energy may change in form, but it cannot be created or destroyed. The bicyclist cannot create energy- she must change some type of energy into the mechanical energy of the bike's turning pedals. Since she does not have a motor on her bike, she must use food energy stored in her body to turn the pedals. The requirement that the total energy of the universe remain constant is called the law of conservation of energy. This law also applies to systems smaller than the universe as long as no energy is allowed to enter or leave the system. For example, we might define a system to be a roller coaster and the surrounding air. At the top of the first hill, all of the roller coaster's energy is potential energy. As it accelerates down the first hill, its potential energy changes to kinetic energy. At the same time, though, the roller coaster loses some energy to air friction and friction between the wheels and the tracks. The friction produces heat energy that flows into the surrounding air from warmed parts of the roller coaster. In addition the roller coaster produces sound energy, which flows out into the air. However, the total energy of the system of the roller coaster and surrounding air remains constant at all points during the ride. You would get the same answer for the total energy if you added up the amount of each form of energy at any instant. You would find that the total energy was equal to the potential energy the roller coaster had at the top of the first hill. Why Conserve Energy?
Many nations of the world depend on coal, oil, and natural gas for sources of energy. These fuels may be used to produce electrical energy, or they may be burned in vehicles to produce mechanical energy. The worldwide demand for energy is becoming so great that a number of scientists fear that we will run dangerously short of coal, oil, and natural gas sometime in the 21st century.
A train carrying coal