Unit 2 Energy

Energy Transformations Law of Conservation of Energy Energy cannot be created or destroyed only transformed to another type of Energy

Where does Energy come from? What is energy ? The stuff inside batteries….. Duh! It makes that bunny go and go and go

Types of Energy Energy is the ability to do work Work is defined as the amount force needed to move an object a certain distance There are two broad categories of energy Potential and Kinetic

Kinetic Energy Energy of motion The formula to calculate it is KE = mass (velocity) 2 2 Forms of Kinetic Energy Electromagnetic (sun or light) Mechanical (motion) Electrical (electrons) Thermal (atoms) Sound (vibration)

Potential Energy Energy an object has because of its position, rather than its motion The type of potential energy we study most of the time is Gravitational potential energy GPE = mass x gravity x height gravity on Earth is 9.8m/sec 2

Potential Energy Forms of Potential Energy Chemical (energy stored in the bonds) Nuclear (energy stored in the nucleus) Gravitational (energy stored in position i.e. height) Mechanical

A ball at the rest has potential energy once it is pushed and begins rolling the potential energy is reduced and the kinetic energy is increased as the ball comes to a stop the kinetic energy begins to decrease as it is converted back to potential energy.

Potential Energy Examples P = m (h) Where m is mass and h is height

Where does Energy come from? The plug in the wall.. Duh!

The Origin of all Energy All energy comes from the sun and is transferred and converted into other forms of energy as needed Energy cannot be created or destroyed it always continues to transform from one form into another

Potential to Kinetic transformations In a pendulum if the pendulum is up and one end it will have the highest potential energy as it moves towards the middle it will have the greatest amount of kinetic energy and then as it passes the middle to rise to the other end the potential energy will increase again but the kinetic energy will decrease In other words the pendulum goes from potential to kinetic and back again in a cycle until (friction) it stops The energy at this point has been transferred to the air which made the pendulum stop Note: a pendulum will never stop if we had no air resistance (friction) to make it stop

The Pendulum

Another Potential to kinetic transformation In a roller coaster or a car on top of a hill it will have the highest potential energy at the top of the hill. The energy is the greatest at the bottom of a drop, before some is translated back into potential energy as the car climbs the next rise.

Other Transformations Energy from the sun travels to earth and begins the process of photosynthesis This is electromagnetic energy traveling from the sun and being converted to chemical energy in the plant When humans and animals eat the plant food they have energy to move This is chemical energy from the plant converted into mechanical energy in the animals

Transformations Cont’d When we plug something into the wall we close a circuit which conducts electrical energy if we use that electricity to turn on a stove or an air conditioner that electrical energy is being converted into thermal energy Gasoline burned in a car making the car run the gasoline is a chemical and when it burns the energy in it’s atoms is released this is chemical energy converted to mechanical

Last examples A lamp being turned on is electrical energy from the socket transferred to light or electromagnetic energy and a little heat given off by the bulb Energy is constantly converted back and forth from potential to kinetic and from one form to another

Heat Energy Transfer Heat or thermal energy always moves from hot to cold Conduction – direct contact with the surface (touching a hot piece of metal) Convection – transferred by cycling in a water or air current (such as the water cycle) Radiation – moving in electromagnetic waves ( like the sun’s rays)