Conservation of Energy

 How did you get to school today?  If you walked, did you get tired? Why do you think you got tired?  If you rode in a vehicle, did the vehicle ever just shut down and stop for no reason?

Energy You were able to travel this morning because of Energy. This is the ability or capacity of any physical system to do Work. All work is done by Energy. Since there are so many different kinds of forces, energy often takes on many different forms.

Two BASIC Forms of Energy There are two basic forms of energy: Kinetic Energy and Potential Energy.

2 Basic Forms of Energy All types of energy fall under these two categories (forms). Kinetic Energy are forms of energy in motion Potential Energy are forms of energy that are stored.

Mechanical Energy  Mechanical energy is due to the position and motion of the object.  What happens to the mechanical energy of an apple as it falls from a tree?

Energy Changes  As the apple falls to the ground, its height decreases. Therefore, its GPE decreases.  The potential energy is not lost… it is converted into kinetic energy as the velocity of the apple increases.  What happens to the mechanical energy?

Mechanical Energy The energy in the system remains constant – the same!!

Swinging Along  Think about the changes in energy when you are on a swing…  At what point do you have the most potential energy?  At what point do you have the most kinetic energy?  What happens to the mechanical energy?

 But how? If I stop pumping while I’m swinging, I stop!! So, where’s the energy?

Mechanical Energy The energy in the system remains constant – the same!!

Energy Changes  You need to remember friction …  As you slow down on the swing, the hooks and the chain rub against each other and air pushes against the rider.

 Friction causes some of the mechanical energy of the swing to change to thermal energy.  Thermal Energy or heat, is the kinetic energy of particles of matter.

Thermal Energy  It is the heat caused by the friction of the molecules moving fast and bumping into each other. That’s why it is kinetic

Changing Forms of Energy  Energy is most noticeable as it transforms from one type to another.  Electrical energy comes from the movement of electrons.  Do you think electricity is potential or kinetic energy? Kinetic!

Examples of Electric Energy Converting to another kind of Energy  Radio electric to sound energy  Lightbulb, electric to light or thermal energy  Hair dryer, electric to thermal energy

Changing forms of Energy  Chemical Energy is the energy that holds bonds between atoms together. This is potential because you don’t get the energy until you break the bonds.

Chemical Energy An example of transforming chemical energy is a car engine. Chemical potential energy in gasoline is transformed into kinetic energy of the car as it moves

Energy in Your Body  Even the energy converted in your body follows the law of conservation of energy.  Chemical potential energy is transferred to kinetic energy that allows your body to move!!

Mechanical Energy The energy in the system remains constant!!

KE and PE  In many situations, there is a conversion between potential and kinetic energy.  The total amount of potential and kinetic energy in a system is called the mechanical energy  Mechanical energy = PE + KE

The Law of Conservation of Energy  The Law of Conservation of Energy states that energy cannot be created or destroyed. It can only be transformed!  The big picture… the total energy in the universe remains constant.

Conservation of Energy  Energy is transformed… not destroyed!!