5.2 Energy

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 speed2 = [kg x (m/s)2] = [(kg x m/s2)(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 • Wnet= ΔKE • Wnet= ΔPE • 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