Potential Energy Objectives P 205-212 Define potential energy Calculate potential energy Compare potential energy to kinetic energy
Potential Energy Measured in joules Stored energy Elastic, chemical, nuclear and gravitational
Elastic Potential Energy
Chemical Potential Energy
Nuclear Potential Energy
Gravitational Potential Energy Energy due to an object’s position above the earth
Weight Related to Gravitational Potential Energy Is not the same as mass Formula: Fg=mg Fg = weight in Newtons (n) m= mass in kg g= acceleration of gravity=9.81m/s2
Why are you weightless on the moon?
Gravitational Potential Energy An object must have a height above ground to have Ep The work required to move an object to a certain height is equal to its potential energy at that height.
Gravitational potential energy Formula Ep = mgh Ep= gravitational potential energy in joules (J) m= mass in kg g= gravity, 9.81m/s2 h=height in meters (m)
Ex) A shelf is 1. 8m above the floor. A book with a mass of 1 Ex) A shelf is 1.8m above the floor. A book with a mass of 1.2kg sits on the shelf. Calculate the gravitational potential energy. Ep = mgh =1.2kg x 9.81m/s2 x 1.8m =21J
Energy Conversions Energy is a conserved quantity: it can not be created or destroyed but it can be converted. Ex) Gravitational energy will be converted to kinetic energy as an object returns to the ground
Ex) A 50. 0kg skier is at the top of a 100m hill Ex) A 50.0kg skier is at the top of a 100m hill. What is his speed at the bottom of the hill?
Pendulum
Ex) If you did 565J of work on a 12kg box carrying it up a flight of stairs, how high are the stairs? Ep = mgh