Conservation of Energy Chapter 13.4 Notes

Energy Transformations Energy readily changes from one form to another For example, think about when you ride a roller coaster – at the top of the first hill, all of the energy is stored as gravitational potential energy – As you begin to fall, the energy is transformed into kinetic energy – When you climb another hill on the coaster, the energy is transformed again back into potential energy – Even though energy can transform, the amount of energy always remains the same

Potential energy can change into kinetic energy, and kinetic energy can change into potential energy

Mechanical Energy Remember that mechanical energy is all of the kinetic and potential energy in a system Mechanical energy can change into other forms of energy—if it did not, then a ball would always bounce back to the same height from where it were dropped and roller coasters would keep going forever

Changing forms of energy Example: when a ball is dropped, not all of its kinetic energy is changed to potential energy. – Some KE compresses the air around the ball, which will release energy as sound – Some KE makes the ball, the air, and ground a little warmer, releasing energy as heat When a roller coaster rolls, it loses some mechanical energy because of friction and air resistance – The energy does NOT disappear though; some of it increases the temperature of the track, the car’s wheels, and the air – Some energy compresses the air and causes a roaring sound

The Law of Conservation of Energy The total amount of energy in the universe never changes, although energy may change from one form to another – Energy never disappears, but it does change form Law of conservation of energy: energy cannot be created or destroyed Energy can be transferred as work or as heat – First law of thermodynamics: for any system, the net change in energy equals the energy transferred as work and as heat; when no energy is transferred as heat or as work, mechanical energy is conserved

Types of Systems Open system: a system in which energy and matter are exchanged with the surroundings Closed system: energy is exchanged with the surroundings, but matter is not Isolated system: neither energy nor matter is exchanged with the surroundings Most real-world systems are open; very few are isolated