Energy

• Chemical energy stores include fuels, food, or the chemicals found in batteries. The energy is transferred during chemical reactions
• Kinetic energy stores describe the energy an object has because it is moving
• Gravitational potential energy stores are used to describe the energy stored in an object because of its position, such as an object above the ground
• Elastic potential energy stores describe the energy stored in a springy object when you stretch or squash it
• Thermal energy stores describe the energy a substance has because of its temperature
• There are many different examples of energy store transfers:

  A) gravitational potential energy decreasing

  B) kinetic energy increasing

  C) heating and sound on impact

  
• The Specific Heat Capacity of a substance is the amount of energy required to raise the temperature of 1 kg of the substance by 1 degrees Celsius
• Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed
• This image describes the change in energy stores of a pendulum.

  A) Maximum GPE of the mass

  B) Maximum GPE of the mass

  C) KE transferred to GPE

  D) GPE transferred to KE

  E) Maximum KE of the mass

  
• As a pendulum swings, there is friction in the fixed point it swings from, and there is friction as the pendulum passes through the air particles. Friction causes energy to be transferred to thermal energy. This means that the fixed point and air around the pendulum gradually get warmer. These stores of thermal energy are less useful. The energy has been dissipated (transferred to the surroundings)

  A) Friction in the fixed point

  B) Friction as the pendulum passes through the air particl

  
• We can reduce unwanted energy transfers by reducing friction, e.g. by using a lubricant such as oil on the fixed point of the pendulum, or removing the air particles from around the pendulum
• As a bungee jumper jumps:

  1. Before the jump, all of the energy in the system is the store of GPE
  2. As the jumper falls, energy is transferred from GPE to KE
  3. When the bungee rope starts to tighten, the KE is at it's maximum
  4. When the rope is fully extended, the KE is at 0 as the jumper is not moving, and all of the energy has been transferred to EPE
  5. The bungee rope recoils and energy is transferred from EPE to KE
  6. During the ascent, energy transfers from KE to GPE
  7. At the top of the ascent, all of the energy is in the GPE store