University:
Winston-Salem Forsyth County Schools
Course:
AP Physics I
Academic year:

2015
Views:

251

Pages:

28
Author:

Genevieve Gross

ENERGY UNIT 3 GOOD MORNING! WARMUP FOR THURSDAY – QUIZ AFTER 1. You pull my turtle up out of the water with 5 N of force. The weight of my turtle pulling down is 2 N. What is the net force in this situation? a) 2.5 N b) 3 N c) 5 N d) 7 N 2. If your mass is 50kg, how would it change if you were on Mars? a) I don’t know, because mass changes with gravity and I need the acceleration of gravity on Mars to figure that out b) 50kg, because mass stays the same. Weight is what changes with gravity 3. How could a small person get more momentum than a larger person? Remember the forumula P=mv • 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 you ever run out of gas and the car stopped? ENERGY You were able to travel this morning because of Energy. Energy makes things GO! Energy allows work to happen All work is done by Energy. Since there are so many different kinds of forces, energy often takes on many different forms. ENERGY EXISTS IN 2 STATES Kinetic Energy and Potential Energy. 2 STATES OF ENERGY Potential Energy- Stored Energy, “unused energy” Kinetic Energy - Energy of moving objects THERE ARE MANY KINDS “FORMS” OF ENERGY We will go over about 6 forms You will Write these on the ENERGY graphic organizer 1)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 FORM • As the apple falls to the ground, its height decreases. Therefore, its Potential Energy PE decreases. • The potential energy is not lost… it is converted into kinetic energy as the velocity of the apple increases. • What happens to the total 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 going? MECHANICAL ENERGY IT is changing forms…it does not disappear... 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 that mechanical energy of the swing to change to thermal energy. We can call this dissipated Energy – Thermal energy from friction 2) ELECTRICAL 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! 3) LIGHT ENERGY 4) SOUND ENERGY • Energy is most noticeable as it transforms from one type to another. • SOUND ENERGY can also make things go • Watch Sound Energy do something EXAMPLES OF ELECTRIC ENERGY CONVERTING TO ANOTHER KIND OF ENERGY • Radio electric sound energy • Lightbulb, electric light thermal • Hair dryer, electric thermal energy 5) CHEMICAL ENERGY (POTENTIAL) 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 EXAMPLE 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 CHEMICAL ENERGY EXAMPLE FOOD!! • 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!! 6) THERMAL ENERGY When energy has turned into heat Heat is Kinetic! • Friction causes some mechanical energy to change to thermal energy. Dissipated Energy – from friction 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. MECHANICAL ENERGY The energy in the system remains constant!! KE and PEg • In many situations, there is a conversion between potential energy due to gravity PEg and kinetic energy KE. • The total amount of potential and kinetic energy in a system is called the mechanical energy (and any dissipated energy) • Mechanical energy = PEg + KE + dissipated CONSERVATION OF ENERGY • Energy is transformed… not destroyed!!