1 Stored Energy Energy of Position Working Energy Energy of Motion

2 Stored Energy becomes Working Energy Potential Energy becomes Kinetic Energy. or in other words… For example… a rubber band zinged from your finger has kinetic energy. While it was stretched, waiting for you to release it, it had potential energy. The rubber band was stationary (not moving), but work had been done on it to move it to its present position. This again is an energy transformation.

3 The formulas to calculate Potential Energy are… Gravitational Potential Energy = mass X gravity’s acceleration X height GPE = mgh Potential Energy = weight X height PE = wh PE is measured in Joules (J) Weight is given in Newtons (N) & height in meters (m) Mass is given in kilograms (kg), gravity’s acceleration is 9.8m/s 2 & height is in meters (m)

4 GUESSRead the problem, draw a picture and write down what is given in the problem. GUESS Write down the unknown variables in the problem. A 17N flower pot is lifted to a height of 3 meters. What is the energy of this object? Problem: Potential Energy W = 17N GivenUnknownEquations NeededSubstitute including unitsSolution GUESS Write down the equation needed to solve the problem. GUESS Substitute the known variables into the equation including the UNITS. GUESS Solve the equation including the UNITS. PE = 51 Joules h = 3m PE = whPE = 17N x 3m

5 GUESSRead the problem, draw a picture and write down what is given in the problem. GUESS Write down the unknown variables in the problem. A 30 kg child climbs 15m up a tree. When she stops to look around, what is the child’s energy? Problem: GPE M = 30kg GivenUnknownEquations Needed Substitute including unitsSolution GUESS Write down the equation needed to solve the problem. GUESS Substitute the known variables into the equation including the UNITS. GUESS Solve the equation including the UNITS. PE = 4410 Joules h = 15m GPE = mgh GPE = 30kg X 9.8m/s 2 x 15m

6

7 Kinetic Energy = ½ (mass x velocity 2 ) Units for Kinetic Energy are – Joules (J) Units for Mass are – kilograms (kg) Units for Velocity are – (m/s) KE = mv 2 2 The formula to calculate Kinetic Energy is…

8 GUESSRead the problem, draw a picture and write down what is given in the problem. GUESS Write down the unknown variables in the problem. What is the energy of a 25kg tennis ball being hit at a velocity of 13m/s? Problem: KE M = 25kg GUESS Write down the equation needed to solve the problem. GUESS Substitute the known variables into the equation including the UNITS. GUESS Solve the equation including the UNITS. KE = Joules v = 13m/s KE = mv 2 2 KE = 25kg (13m/s) 2 2 KE = 25kg (169m 2 /s 2 ) 2 KE = 4,225kg.m 2 /s 2 2 SolutionSubstitute including unitsEquations NeededUnknownGiven

9