Energy: the ability to do work or to cause a change Energy Notes Energy: the ability to do work or to cause a change

Energy Work is done when a force causes something to move. Any matter has energy if it can produce a change in itself or in its surroundings When work is done and a change occurs, energy moves from place to place or changes from one form of energy to another.

An Energy Analogy An Energy Analogy: Money can be used to help you understand energy   If you have $100, you could store it in a variety of different forms: 1. Cash in your wallet 3. A Bank Account 2. Gold or Silver Coins 4. Traveler’s Check

You could transfer money to different forms: An Energy Analogy You could transfer money to different forms: Deposit cash into a bank account 2. Trade the cash for gold It’s still money, regardless of the form, and the same is true for energy!

Kinetic Energy Kinetic Energy (KE): energy a moving object has because of its motion Depends on Mass and Velocity

Potential Energy Potential Energy (PE): stored energy associated with position

Example: A hanging apple in a tree Potential Energy Example: A hanging apple in a tree It has stored energy because of its position above the surface If it stays in the tree, it will keep its stored energy due to its height above the ground If it falls, the stored energy of position is converted to energy of motion (Kinetic)

Potential Energy Elastic Potential Energy: energy stored by something that can stretch or compress. Example: A stretched rubber band or a spring (When you let a rubber band go, it flies across the room as kinetic energy)

Potential Energy Chemical Potential Energy: potential energy stored in the chemical bonds of atoms and chemical compounds that is released when the bonds break as in a chemical reaction.

Chemical Potential Energy Examples: Natural Gas, Gasoline, Food When natural gas is burned, those bonds are broken, & energy is released Digestion of Food Releases Energy Plants Store Energy after Photosynthesis, converting sunlight to sugars Note: One food calorie (C) is equal to one kilocalorie (kC) which is equal to 4180 Joules.

Gravitational Potential Energy Potential Energy is sometimes called: Gravitational Potential Energy (GPE)

PE and KE POTENTIAL ENERGY KINETIC ENERGY Water Behind a Dam Waterfall Car Parked at Top of Hill Car Rolling Down a Hill Gasoline Engine Runs Food You Run a Mile

Mechanical Energy Mechanical Energy (ME): the total amount of potential and kinetic energy in a system. ME = PE + KE *An object with ME can do work on another object. It puts things in motion. It moves cars and lifts elevators. A machine uses ME to do work, and so do our bodies.

Energy Transformations Energy Transformations: a change from one form of energy into another

Energy Transformations Single Transformation: one form of energy is transformed to do work Example: a toaster changes electrical energy to thermal energy to heat bread. Example: An apple accelerates to the ground after it comes loose from the tree and its potential energy becomes kinetic energy.

Energy Transformations Example: A baseball’s curved path after the ball is hit by the bat, where kinetic energy and potential energy are converted into each other as the ball rises and falls.

Energy Transformations Low KE/High GPE High KE/Low GPE High KE/Low GPE

Another Example Energy Transformations in a Pendulum: There is a continuous transformation between kinetic and potential energy in a pendulum. At the highest point of the swing, when the pendulum has no movement, gravitational potential energy is the greatest. As it swings down, the potential energy is transformed into kinetic energy and reaches its greatest kinetic energy as the bottom of the swing. This repeats itself as the pendulum swings up to the highest position on the other side.

Pendulums and Transformations

Law of Conservation Law of Conservation of Energy: when one type of energy transforms into another, no energy is created nor destroyed. It simply changes form. Total amount of energy is the same before and after any transformation.

Conservation of Energy & Friction But what about FRICTION? When energy is lost due to friction, the energy has transformed from kinetic to thermal energy (heat). The energy is not destroyed, it has just changed form. Friction transforms mechanical energy into thermal energy, which is how you warm your hands when rubbing them together, and why no machine is 100% efficient. Mechanical energy is transformed into thermal energy due to friction.