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Uploaded byPhysics Amal Sweis
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Energy physics

This document discusses concepts related to kinetic energy, work, potential energy, and machines. It defines kinetic energy as the energy of motion, and states that an object's kinetic energy depends on its mass and speed. Kinetic energy is calculated using the formula KE=1/2mv^2. Work is done when an object's kinetic energy changes, and work depends on the applied force and distance moved. Potential energy is stored energy due to an object's position or arrangement, such as gravitational potential energy calculated as mgh. Mechanical advantage measures how machines multiply force, while efficiency indicates the percentage of energy input that does useful work.

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Aya Sharaireh 9 A JUBILEE
Kinetic Energy  If 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.
Kinetic Energy  An 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.
Kinetic Energy  In symbols: KE = 1 2 mv2
Kinetic Energy Kinetic energy is a scalar quantity. Common units of kinetic energy: Joules An object with mass of 1 kg, moving at 1 m/s, has a kinetic energy of 0.5 Joule.
Work When the kinetic energy of an object changes, work has been done on the object. Units of work: Joules Work is a scalar quantity.
Work  Work 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.
Work  If the force on the object is in the direction the object moves, the work done is: W = Fx F x
Work  If the direction of the force is opposite the direction the object moves, work is: W = -Fx F x
Force is NOT Work  If 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. F x W = 0
Work and Kinetic Energy  The work done on an object by the net force equals the object’s change in kinetic energy. Wnet = ∆KE
Potential Energy  Sometimes work is not converted directly into kinetic energy. Instead it is “stored”, or “hidden”.  Potential energy is stored energy or stored work.
Potential Energy  Potential energy is energy that an object (system) has due to its position or arrangement.
Calculating Potential Energy  To calculate the potential energy of a particular arrangement: 1. Pick a position or arrangement that you want to call the “potential energy = 0” situation.
Calculating Potential Energy 2. The 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
Conservative Forces  Energy 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.
Gravitational PE  The 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
Mechanical Energy  Mechanical Energy = PE + KE
Conservation of Energy  If no external forces act on a system, the total energy of the system will remain constant.
Power  Power is the rate work is done. Power = ∆Work time W P t
Power  Units of power: 1 Joule/sec = 1 Watt  1000 Watts = 1 kilowatt  Power is a scalar quantity.
(Simple) Machines  A machine is a mechanical device used to do work.  Examples of simple machines:  Inclined plane  Lever  pulley
(Simple) Machines  A machine can never output more work (energy) than is put into it.  At best, Workout = Workin Machine Workin Workout
Mechanical Advantage  Machines can’t multiply work or energy, but they can multiply force. Mechanical advantage measures how much a machine multiplies force. MA = Force machine exerts Force you exert
Efficiency  The 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. Efficiency = Useful work done Energy input x 100%
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