• The principle of conservation of energy states that:

Energy cannot be created or destroyed, it can only be transferred from one store to another

• This means the total amount of energy in a?closed system?remains?constant?but can change?where, and?how, it is stored
• Energy can therefore not necessarily be 'lost', but just transferred into?wasted energy?(often heat)
• Conservation of energy applies to?all?energy systems

Example 1: A Television

• The energy changes in?televisions?are:

electrical energy ? light energy + sound energy + thermal energy

• Light and sound energy are?useful?energy transfers whereas thermal energy (from the heating up of wires) is?wasted

Useful and wasted energy conversions for a television

Example 2: Heaters

• The energy changes in an?electrical heater: 

  electrical energy ? thermal energy + sound energy + light energy

   

• In a?gas cooker, the energy transfers are similar but the initial source of energy is different:

chemical energy ? thermal energy + sound energy + light energy

• In both these cases, thermal energy is?useful, whereas sound and light are not

Useful and wasted energy conversions in an electric heater and gas cooker

Example 3: Rollercoasters

• A rollercoaster increases its speed as it travels down a steep section of track and gains?kinetic energy?(KE)
• When the rollercoaster travels up a steep section of track, this kinetic energy is transferred into?gravitational potential energy?(GPE)
• These energy changes happen several times during a rollercoaster ride as the track goes up and down and around

• As the rollercoaster in the diagram travels from?A?to?D, the energy changes that take place are:

GPE ? KE ? GPE ? KE

• Some energy is transferred to the surroundings as heat and sound energy too
• At point?A:
  • The rollercoaster is raised above the ground, therefore it has?GPE
  • As it travels down the track,?GPE?is converted to?KE?and the roller coaster speeds up

   

• At point?B:
  • KE?is converted to?GPE?as the rollercoaster rises up the loop

   

• At point?C:
  • This?GPE?is converted back into?KE?as the rollercoaster travels back down the loop

   

• At point?D:
  • The flat track means the rollercoaster only has?KE

   

Example 4: Trampoline

• When jumping on a trampoline the energy changes are:

elastic potential energy ? kinetic energy ? gravitational potential energy

• Some energy is transferred to the surroundings as heat and sound energy too

Energy conversions for someone jumping on a trampoline

轉(zhuǎn)載自savemyexam