Potential Energy P 205 212 Objectives Define potential

Potential Energy P 205 -212 Objectives Define potential energy n Calculate potential energy n Compare potential energy to kinetic energy n

Potential Energy n Measured in joules n Stored energy n Elastic, chemical, nuclear and gravitational

Elastic Potential Energy

Chemical Potential Energy

Nuclear Potential Energy

Gravitational Potential 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. 81 m/s 2

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) n m= mass in kg n g= gravity, 9. 81 m/s 2 n h=height in meters (m)

Ex) A shelf is 1. 8 m above the floor. A book with a mass of 1. 2 kg sits on the shelf. Calculate the gravitational potential energy. Ep = mgh =1. 2 kg x 9. 81 m/s 2 x 1. 8 m =21 J

Energy Conversions n Energy is a conserved quantity: it can not be created or destroyed but it can be converted. n Ex) Gravitational energy will be converted to kinetic energy as an object returns to the ground

Ex) A 50. 0 kg skier is at the top of a 100 m hill. What is his speed at the bottom of the hill?

Pendulum

Ex) If you did 565 J of work on a 12 kg box carrying it up a flight of stairs, how high are the stairs? Ep = mgh