Transcript What is Energy?
What is Energy? Energy, work and Power • Energy is the ability to do work or cause change Work and Energy • When an object does work on another object, some energy is transferred to the object… • So work = a transfer of energy • Both are measured in Joules (J) Power and Energy • Power is the rate at which work is done • Power is therefore the rate at which energy is transferred • Power = Energy Transferred time Kinetic Energy • Two basic kinds of energy – kinetic and potential • Energy that an object has due to its motion = kinetic energy (KE) • “Kinetos” in Greek means motion Factors Affecting Kinetic Energy • Depends on both mass and velocity • When mass goes up, KE goes up; when velocity goes up, KE goes up • Idea similar to momentum? Calculating KE • KE = ½ mv2 • Mass is in Kg • Velocity is in m/s • Change in velocity has greater affect on kinetic energy than change in mass Potential Energy • Stored energy that results from the position or shape of an object • Energy that has the potential to do work Gravitational Potential Energy • Stored energy that depends on the height of an object • The higher an object is the more GPE it has. Calculating GPE • GPE = MGH • GPE = mass x 9.8m/sec2 x height • Mass is in Kg and height is in m FYI • Mass * 9.8 m/sec2= Weight (and weight is a force) • So we have F * D Elastic Potential Energy • Stored energy associated with objects that can be stretched or compressed • Examples are springs like those in mattress, a slinky, an elastic band to put in hair, a rubber band, a bow to shoot arrows and many more! FYI: Calculating EPE • Technically there is a formula used to calculate this: PE = ½ kx2 where “k” is a constant and “x” is the distance the spring or material is stretched or compressed from its original state. You will not be asked to calculate this type of energy but you should be aware that it can be found. If a car that has a mass of 80kg is rolling down a roller coaster track, and it has a velocity of 15m/sec, what is the Kinetic Energy of the car at this point in its motion? • KE = ½ mv2 • KE = ½ 80 kg * (15 m/sec)2 • KE = 9000 Joules A person with a mass of 58kg is sitting on the top row of the bleachers 21 meters off the ground at a football game, calculate his GPE. • GPE = mass x 9.8 m/sec2 x height • GPE = 58 kg x 9.8 m/sec2 x 21 m • GPE = 11936.4 Joules Magic Triangles KE .5M V2 • KE = 0.5 M x V2 • V2 = KE / 0.5M • 0.5M = KE / V2 Remember MG = Weight! (a force!) GPE MG • GPE = MGH • MG = GPE / H • H = GPE / MG H