Energy Notes (Chapter. 5) 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 Coins4. Traveler’s Check

An Energy Analogy You could transfer money to different forms: 1.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 Formula: m=mass v=velocity Units: ½ (Kg)(m/s) 2 = kgm 2 /s 2 = Joule  J KE 0.5 m v2v2 KE = ½mv 2

Kinetic Energy Example: How much kinetic energy does a 0.5 kg ball have when it’s moving at 2 m/s? 1.KE = ?2. KE = ½mv 2 m = 0.5 kg v = 2 m/s 3. KE = ½ (0.5kg)(2m/s) 2 = 1 Joule or 1J

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

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) Formula: = mass x gravity x height PE = wh = weight x height (Remember: weight = mass x gravity) (gravity = 9.8 m/s 2 ) PE = mgh

Gravitational Potential Energy The higher something is above the ground, the more P.E. it has PE mgh

PE and KE POTENTIAL ENERGYKINETIC ENERGY Water Behind a DamWaterfall Car Parked at Top of HillCar Rolling Down a Hill GasolineEngine Runs FoodYou 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.

Other Forms of Energy Thermal Energy: caused by the constant motion that the particles of the object are in. *Combines the PE and KE of the particles of an object *Particles move faster when heated and slower when cooled Example: Ice Cream melting on a hot day

Heat Transfer Heat Transfer: 3 ways heat can move: Conduction ConvectionRadiation

Heat Transfer Conduction: heat is transferred from one particle of matter to another without the movement of matter through direct contact or touching. Example: feet on hot sand or a heating pad on your sore back

Heat Transfer Convection: Heat is transferred by the movement of currents within a fluid. *less dense, heated particles move to the top and cooler, denser particles flow down to take their place, creating convection currents. Example: Warm air rises and cold air sinks

Heat Transfer Radiation: Transfer of energy by electromagnetic waves and does not require direct matter to matter contact. Example: Sunlight (solar energy) reaching Earth’s surface Example: Warming your hands by a fire

Electrical Energy Electrical Energy: the flow of electric charges in the form of moving electrons, which are the negative charged particles in an atom. Example: Stored in a battery (Potential) Example: Lightning Strike (Kinetic)

Nuclear Energy Nuclear Energy: potential energy that is stored in the nucleus of an atom Fission: Nuclear energy released when an atom splits as in nuclear power plants Fusion: energy released when the nuclei of atoms fuse together as in solar energy when the sun fuses Hydrogen atoms into Helium

Electromagnetic Energy Electromagnetic Energy: energy that travels in waves have both electric and magnetic properties. *can travel through the vacuum of space Examples: sunlight, radio waves, x-rays, microwaves, IR rays, UV rays, visible light, sound waves

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 High KE/Low GPE Low KE/High GPE

Energy Transformations Multiple Transformation: a series of transformations are needed to do work Example: mechanical energy is used to strike a match to produce thermal energy, which causes the particles of the match head to release stored chemical energy, which is transformed into thermal and electromagnetic energy as heat and light are produced.

Energy Transformations 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 Just like the Law of Conservation of Mass or Matter which states that in a reaction, mass and matter cannot be created nor destroyed, it simply changes form…the

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.