Presentation on theme: "Ch 8 Energy Notes Concept Summary Batesville High School Physics"— Presentation transcript:
1 Ch 8 Energy Notes Concept Summary Batesville High School Physics
2 Ch 8 Energy NotesKinetic EnergyIf an object is moving, it has energy. (Be careful, the converse of this statement is not always true!)This energy is called kinetic energy - the energy of motion.
3 Kinetic Energy An object’s kinetic energy depends on: Ch 8 Energy NotesKinetic EnergyAn object’s kinetic energy depends on:the object’s mass.Kinetic energy is directly proportional to mass.the object’s speed.Kinetic energy is directly proportional to the square of the object’s speed.
4 Ch 8 Energy NotesKinetic EnergyIn symbols:1KE =mv22
5 Kinetic Energy Kinetic energy is a scalar quantity. Ch 8 Energy NotesKinetic EnergyKinetic energy is a scalar quantity.Common units of kinetic energy: JoulesAn object with mass of 1 kg, moving at 1 m/s, has a kinetic energy of 0.5 Joule.
6 Ch 8 Energy NotesWorkWhen the kinetic energy of an object changes, work has been done on the object.Units of work: JoulesWork is a scalar quantity.
7 Work Work depends on: The amount of force applied to the object. Ch 8 Energy NotesWorkWork depends on:The amount of force applied to the object.The distance that the object moves while the force is applied.The direction of the force with respect to the direction the object moves.
8 Ch 8 Energy NotesWorkIf the force on the object is in the direction the object moves, the work done is:W = FxFx
9 Ch 8 Energy NotesWorkIf the direction of the force is opposite the direction the object moves, work is:W = -FxFx
10 Ch 8 Energy NotesForce is NOT WorkIf the force is perpendicular to the direction the object moves, the work done is 0.If the object doesn’t move, the work done is 0.FW = 0x
11 Work and Kinetic Energy Ch 8 Energy NotesWork and Kinetic EnergyThe work done on an object by the net force equals the object’s change in kinetic energy.Wnet = DKE
12 Ch 8 Energy NotesPotential EnergySometimes work is not converted directly into kinetic energy. Instead it is “stored”, or “hidden”.Potential energy is stored energy or stored work.
13 Ch 8 Energy NotesPotential EnergyPotential energy is energy that an object (system) has due to its position or arrangement.
14 Calculating Potential Energy Ch 8 Energy NotesCalculating Potential EnergyTo calculate the potential energy of a particular arrangement:Pick a position or arrangement that you want to call the “potential energy = 0” situation.
15 Calculating Potential Energy Ch 8 Energy NotesCalculating Potential EnergyThe potential energy of any other position or arrangement equals the negative of the work that the conservative force does in changing from the potential energy = 0 situation to that one.PE = - WorkF
16 Ch 8 Energy NotesConservative ForcesEnergy or work is stored when a force does work “against” a force such as the gravitational force or a Hooke’s Law (spring) force.Forces that store or hide energy are called conservative forces.
17 Gravitational PE GPE = mgh Ch 8 Energy NotesGravitational PEThe gravitational potential energy of an object at height h equals the negative of the work that gravity does when the object is lifted from the PE = 0 position.GPE = mgh
18 Ch 8 Energy NotesMechanical EnergyMechanical Energy = PE + KE
19 Conservation of Energy Ch 8 Energy NotesConservation of EnergyIf no external forces act on a system, the total energy of the system will remain constant.
20 Power DWork Power = time W P t Power is the rate work is done. Ch 8 Energy NotesPowerPower is the rate work is done.DWorkPower =timeWPt
21 Power Units of power: 1 Joule/sec = 1 Watt 1000 Watts = 1 kilowatt Ch 8 Energy NotesPowerUnits of power: 1 Joule/sec = 1 Watt1000 Watts = 1 kilowattPower is a scalar quantity.
22 (Simple) Machines A machine is a mechanical device used to do work. Ch 8 Energy Notes(Simple) MachinesA machine is a mechanical device used to do work.Examples of simple machines:Inclined planeLeverpulley
23 Ch 8 Energy Notes(Simple) MachinesA machine can never output more work (energy) than is put into it.At best,Workout = WorkinMachineWorkoutWorkin
24 Ch 8 Energy NotesMechanical AdvantageMachines can’t multiply work or energy, but they can multiply force. Mechanical advantage measures how much a machine multiplies force.Force machine exertsMA =Force you exert
25 Efficiency Useful work done Efficiency = x 100% Energy input Ch 8 Energy NotesEfficiencyThe efficiency of a machine tells how much of the energy (work) that goes into the machine actually does useful work.It is usually expressed as a percent.Useful work doneEfficiency =x 100%Energy input