1. 5.2 Energy pp 172 -180 Mr. Richter

2. Agenda  Warm-Up  Review HW  Introduction to Energy  Notes:  Kinetic Energy  Potential Energy  Gravitational  Other forms  Work and Energy  Lab Friday

3. Objectives: We Will Be Able To…  Define energy and identify several forms of energy.  Define and calculate kinetic energy.  Classify, define and calculate different types of potential energy.  Understand the relationship between work and energy.

4. Warm-Up:  Review: What is energy?  You may need to review your notes from the first week of school.  Write a 1-sentence definition in your notes.

5. Energy

6. What is Energy?  Review: Energy is a measure of the ability to cause change in a system.  Energy is like the currency of the universe. Physics money.  If you have energy, you can make a change.  If you have no energy, no change can be made.

7. Kinetic Energy The Energy of Motion

8. Kinetic Energy  Objects in motion have the ability to cause change.  A moving wrecking ball can cause change in the shape of a building.  Moving hands can cause a change in temperature.  Kinetic energy is the energy of an object due to its motion.  You can also think of kinetic energy as the amount of energy that would have to be used to stop an object.

9. Kinetic Energy  Kinetic energy depends on:  mass  speed  Units:  mass x speed 2 = [kg x (m/s) 2 ] = [(kg x m/s 2 )(m)] = N-m = J!  The units of energy (all forms) are Joules [J]!

10. Warm Up: Calculating Kinetic Energy  A 7.00 kg bowling ball moves at 3.00 m/s. How much kinetic energy does the bowling ball have?  31.5 J

11. Potential Energy The Energy of Position

12. Potential Energy  The word potential implies that something could happen. An object could cause a change.  Objects in certain positions have the potential to cause change. Potential energy is the energy associated with the object due to the position of the object.  Potential energy is stored energy.

13. Gravitational Potential Energy  Falling objects gain speed, and therefore gain the ability to cause change. Therefore, any object positioned to fall has potential energy.  Gravitational potential energy is the energy of an object due to its position relative to the Earth (or other source of gravity).  Gravitational potential energy depends on how far something will fall, not necessarily its distance from the ground: height.

14. Calculating Gravitational Potential Energy  A 20.0 kg anvil is positioned to crush the roadrunner 15.0 m below. How much potential energy does the anvil have?

15. Other types of Potential Energy  Elastic: when a spring or rubber band is stretched or compressed  Electrical: when electrons want to move from one place to another

16. Work and Energy Two peas in a pod.

17. Work and Energy  Another definition for work:  The amount of energy transferred from one object to another, or from one form to another.  Work done = change in energy  The amount of work needed to speed up an object is equal to the change in kinetic energy of the object.  The amount of work needed to lift an object is equal to the change in the potential energy of the object.

18. Calculations with Work and Energy  W net = Δ KE  W net = Δ PE  A 75 kg bobsled is pushed along a horizontal surface by two athletes. After the bobsled is pushed a distance of 4.5 m starting from rest, its speed is 6.0 m/s. Find the magnitude of the net force on the bobsled.

20. Wrap-Up: Did we meet our objectives?

21. Homework