KINETIC AND POTENTIAL ENERGY Chapter 6 (cont.)
The Two Types of Mechanical Energy Energy- the ability to do work- measured in joules Potential Energy- energy that arises because of an object s position Kinetic Energy- energy of motion possessed by moving objects
6.4 Potential Energy is Stored Energy Energy of position In a stored state, energy has the potential to do work, but it is not yet doing it Ex: archer drawing back his bow
Ex. Roller coaster sitting at the top of the hill not moving
Formula gravitational potential energy = weight x height (Joules) = (Newtons) x (Meters) Weight is equal to mass multiplied by the acceleration due to gravity or: PE= mgh
How many joules of potential energy does a 1 newton book gain when it is elevated to 4m?
How many joules of potential energy does a 1 newton book gain when it is elevated to 4m? PE = (1N) x (4m)
How many joules of potential energy does a 1 newton book gain when it is elevated to 4m? PE = (1N) x (4m) = 4 J
What is the potential energy of a rock that has a mass of 2 kg and is elevated to a height of 4m?
What is the potential energy of a rock that has a mass of 2 kg and is elevated to a height of 4m? PE= mgh
What is the potential energy of a rock that has a mass of 2 kg and is elevated to a height of 4m? PE= mgh = (2kg)(9.8m/s 2 )(4m)
What is the potential energy of a rock that has a mass of 2 kg and is elevated to a height of 4m? PE= mgh = (2kg)(9.8m/s 2 )(4m) = 78.4 J
What is the mass of a boulder that is elevated 5 m and has a potential energy of 295 J?
What is the mass of a boulder that is elevated 5 m and has a potential energy of 295 J? 295 J = (5m) (9.8m/s 2 ) (m)
What is the mass of a boulder that is elevated 5 m and has a potential energy of 295 J? 295 J = (5m) (9.8m/s 2 ) (m) = 6.02 kg
6.5 Kinetic Energy is Energy of Motion Kinetic energy depends on mass and speed (or velocity) The faster an object moves, the more kinetic energy it has Kinetic Energy= 1/2 mass x velocity 2
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have?
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2 1 J = 1/2 (m) (30 m/s) 2
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2 1 J = 1/2 (m) (30 m/s) 2 m = 0.0022 kg
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2 1 J = 1/2 (m) (30 m/s) 2 m = 0.0022 kg KE = 1/2 (0.0022) (60 m/s) 2
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2 1 J = 1/2 (m) (30 m/s) 2 m = 0.0022 kg KE = 1/2 (0.0022) (60 m/s) 2 = 4 J
Ex: a car travels at 30m/s and has kinetic energy of 1 J. If it travels twice as fast, 60m/s, how much kinetic energy will it have? KE= 1/2 mv 2 1 J = 1/2 (m) (30 m/s) 2 m = 0.0022 kg KE = 1/2 (0.0022) (60 m/s) 2 = 4 J
How much kinetic energy does a 2kg boulder have when it is dropping at 8m/s?
How much kinetic energy does a 2kg boulder have when it is dropping at 8m/s? KE= 1/2 mv 2
How much kinetic energy does a 2kg boulder have when it is dropping at 8m/s? KE= 1/2 mv 2 KE = 1/2 (2kg) (8m/s) 2
How much kinetic energy does a 2kg boulder have when it is dropping at 8m/s? KE= 1/2 mv 2 KE = 1/2 (2kg) (8m/s) 2 = 64 J
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it s moving 3 times as fast?
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it s moving 3 times as fast? KE = 1/2 m v 2
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it s moving 3 times as fast? KE = 1/2 m v 2 1/2 m 3v 2
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it s moving 3 times as fast? KE = 1/2 m v 2 1/2 m 3v 2 = 9 times as far
When the brakes of a car are locked, the car skids to a stop. How much farther will the car skid if it s moving 3 times as fast? KE = 1/2 m v 2 1/2 m 3v 2 = 9 times as far
6.6 Work- Energy Theorem To increase (or decrease) the kinetic energy of an object, work must be done on it Work = KE The work in this equation is the net work - work based on the net force
6.7 Conservation of Energy Energy cannot be created or destroyed; it may be transformed from one form into another or transferred from one object to another, but the total amount of energy never changes In other words: KE = PE 1/2 mv 2 = mgh
As kinetic energy increases, potential energy decreases.