Conservation of Energy Section 3 Conservation of Energy

Essential Questions What is the law of conservation of energy? What is mechanical energy? Why is mechanical energy not always conserved? How are power and energy related?

Review Vocabulary friction: a force that opposes the sliding motion of two surfaces that are touching each other

New Vocabulary law of conservation of energy mechanical energy power

The Law of Conservation of Energy The law of conservation of energy states that energy cannot be created or destroyed. Energy can only be converted from one form to another or transferred from one place to another. (Total energy remains constant) For the roller-coaster cars, energy is converted back and forth between energy and gravitational potential energy. Some kinetic energy is converted to other forms of energy. The total amount of energy is constant. Shenval/Alamy Images

Energy Transformations Examples: Which types of energy do they have? The sun warming your skin. An apple falling off of a tree Eating a granola bar. Driving a car. Riding a bike. Types of energy include: mechanical, electrical, chemical, thermal, and radiant. Mechanical Energy Transformations often describe the energy transformations in bicycles, roller coasters, swings, falling objects, and projectiles. ME is the sum of the KE and PE of the objects in a system. Includes KE, EPE, and GPE of objects but not nuclear, thermal, or chemical PE

The mechanical energy of the bat-ball-Earth system remains constant as the ball rises and falls.

Energy Transformations A ride on a swing illustrates how kinetic energy changes to potential energy and back to kinetic energy. The Columbus Dispatch

Other Energy Transformations: Energy transformations can be affected by other forms of energy or forces. Ex. If you don’t keep getting pushed on a swing or pump, the swing eventually stops. Why??? Air resistance is a force slowing down the velocity of the swing Friction is a force going against the swing on the metal swing itself. To keep swinging, you need more mechanical energy (pumping). Electrical energy is energy used to run electrical devices. Like TV’s, toasters, wash machines, and your stove. Chemical energy is the energy stored in fuels, plants, or the food we eat. Energy from food is measured in Calories. 10 calories is about 40,000 Joules Power is the rate at which energy is converted. It is measured in Watts which is 1 Joule per second. Electrical tools and appliances have power ratings. P = Work energy/ Time