Objectives Define work in terms of energy. Distinguish between potential and kinetic energy. Describe how the kinetic energy of an object depends on mass and speed. State the law of conservation of energy

Energy The ability to do work is energy. Energy is also measured in Joules.

Energy Potential energy is stored energy. Gravitational Potential Energy is potential energy that depends on an elevated position It is equal to the work done against gravity in lifting the object It can be calculated by multiplying the weight of the object by the height the object is lifted PE = weight × height = mass × g × height PE = mgh (g=10m/s2)

How much work is done lifting the 200N box to a height of 4m? Weight = 200 N How much work is done lifting the 200N box to a height of 4m? How much work is done sliding the 200N box up the ramp to the same height? How much force is required to slide the 200N box up the ramp to the same height?

How much potential energy does the box have at the bottom of the ramp? Weight = 200 N How much potential energy does the box have at the bottom of the ramp? How much potential energy does the box have at the top of the ramp? What is the change in potential energy from the bottom to the top?

Energy Kinetic energy is energy of motion Kinetic energy depends on the mass and the speed of an object It is equal to half of the mass of the object multiplied by the square of the speed KE = ½ mv2

Energy PE PE m g h w h mass in kg g = 10 m/s2 weight in N

Energy KE ½ m v2 Divide the mass by 2 Square the velocity

Energy 1. Calculate the potential energy if 15 kg is lifted to a height of 3 meters.

Energy 2. What is the kinetic energy of a 30 kg mass moving at 5 m/s?

Energy 3. Calculate the potential energy if 35 N is lifted to a height of 7 meters.

Energy 4. What is the kinetic energy of a 100kg mass moving at 2 m/s?

Law of 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.

Law of Conservation of Energy KE = _______ PE = 500 J PE = 300 J PE = 100 J PE = 0 J at rest

Law of Conservation of Energy At which position is the potential energy the greatest? At which position is the kinetic energy the greatest? At which position is the kinetic energy the smallest? At which position is the potential energy the smallest? At which position is the speed the greatest? 1 5 2 4 3

Law of Conservation of Energy

Law of Conservation of Energy