1. Unit 07 “Work, Power, Energy and Energy Conservation” The Conservation of Mechanical Energy Kinetic and Potential Energy

2. Kinetic Energy EquationUnits KE = ½mv 2 The Energy of Motion KE = ½(mass)x(velocity) 2 Joules (J) kgm 2 /s 2 If the object is moving it has Kinetic Energy Ask … “Is it moving?”

3. Potential Energy Equation The Energy of Position PE g = mgh PE g =(mass)x(gravity)x(height) Units Joules (J) kgm 2 /s 2 If the object is above the ground it has Potential Energy Ask … “Is it above the ground?”

4. The Law of the Conservation of Energy states that Energy can convert from one form to another form!

5. Quick Video Clip http://bit.ly/pY8h6o

6. To identify each type of Mechanical Energy ask the following questions: Kinetic Energy: (KE) – Is the object moving? Gravitational Potential Energy: (PE g ) – Is the object above the ground? Elastic Potential Energy: (PE e ) – Is a spring compressed or an elastic stretched out?

7. Identify the types of Mechanical Energy the object has at each point.

8. PE g (above the ground) KE (moving) PE g (above the ground) KE (moving) KE (moving)

9. Identify the types of Mechanical Energy the Pogo Stick has at each point.

10. PEePEe + KE KEPEg + KE PEgPEg + KE KE PEe + KE PEe

11. The Law of the Conservation of Mechanical Energy Pendulum “bob”

12. The Law of the Conservation of Mechanical Energy Pendulum “bob” Mechanical Energy is conserved when no dissipative forces are present. Total mechanical energy stays the same as long as there is no friction! PEg KE KE + PEg PEg = 500J

13. Note: Point 1 is the highest and Point 2 and 4 are “on the ground” Look at the rollercoaster below.  Identify if the rollercoaster car has Gravitational Potential Energy, Kinetic Energy or both at each point.  Fill in the table identifying the amount of kinetic and potential energy for each point.

14. Note: Point 1 is the highest and Point 2 and 4 are “on the ground” Look at the rollercoaster below.  Identify if the rollercoaster car has Gravitational Potential Energy, Kinetic Energy or both at each point.  Fill in the table identifying the amount of kinetic and potential energy for each point. PE g KE KE + PE g KE KE + PE g

15. Quick Video Clip http://www.teachersdomain.org/asset/mck05 _int_rollercoaster/ http://www.teachersdomain.org/asset/mck05 _int_rollercoaster/

16. Point 1Point 2Point 3Point 4Point 5 PE g 750 J600 J KE400 J ME

17. Point 1Point 2Point 3Point 4Point 5 PE g 750 J600 J KE400 J ME 0 J 750 J 150 J 350 J0 J 750 J 0 J 750 J

18. Problem #1 Calculate the potential energy of the 15kg rock at the top of a 30m high cliff.  What is the kinetic energy of the rock at the bottom of the cliff?

19. Problem #1 Calculate the potential energy of the 15kg rock at the top of a 30m high cliff.  What is the kinetic energy of the rock at the bottom of the cliff right before it hits the ground? PE = ? m = 15kg h = 30m PE KE PE = mgh PE = (15kg)(9.8m/s 2 )(30m) PE = 4410 J ME top = ME bottom PE top = KE bottom 4410J = KE =4410J

20. Problem #2 Calculate the kinetic energy of the 20kg person moving at 6m/s at the bottom of a hill.  What is the potential energy of the person at the top of the hill?

21. Problem #2 Calculate the kinetic energy of the 20kg person moving at 6m/s at the bottom of a hill.  What is the potential energy of the person when they come to rest at the top of the hill? KE PE KE = ? m = 20kg v = 6m/s KE = ½mv 2 KE = ½ (20kg)(6m/s) 2 KE = 360 J ME top = ME bottom KE bottom = PE top 360J = PE =360J