Work – Energy Theorem

1. Work – Energy Theorem Feb. 19 & 20

2. 10 minutes to complete #1-5!

3. Volunteers to share? It increased Friction, transfers of energy, etc.

4. Volunteers to share? • If work is done on an object, the object acquires the ability to do work

5. 9.3Mechanical Energy When work is done to raise a bowling ball, the bowling ball acquires the ability to do work on an object it hits when it falls.

6. 9.3Mechanical Energy When work is done to wind a spring mechanism, the spring acquires the ability to do work on various gears to run a clock, drive a car, ring a bell, or sound an alarm.

7. Volunteers to share? • If work is done on an object, the object acquires the ability to do work • Something is acquired in order for an object to have the ability to do work • The “something” is MECHANICAL ENERGY 2 types: PE & KE

8. 8.4 POTENTIAL ENERGY, aka PE (pgs 106-107) • An object may store energy by virtue of its position • This energy that is stored and held in readiness is called potential energy (PE) • In other words, this PE has the potential of doing work on something • Examples: • Compressed spring or stretched rubber band (tension) • Electrical energy (battery) • Gravitational potential energy • Grav. PE = mgh • The amount of gravitational potential energy possess by an object is equal to the work done against gravity in lifting it.

9. 8.5 KINETIC ENERGY, aka KE (pg 108) • KINETIC ENERGY IS NOT MOMENTUM! • If an object is moving, then it is capable of doing work • It has energy of motion, or KINETIC ENERGY • The KE of an object depends on its mass and on its speed • KE = ½ m v2 • The KE of a moving object is equal to the WORK required to; • Bring it TO that speed, from rest….or • The work the object CAN do while being brought to rest.

10. The WORK-ENERGY THEOREM THEN… ENERGY changes IF… IF… WORK Is done THEN…

11. Like a wrecking ball! • Not this one!!!! (That’s a train wreck)

12. Like a wrecking ball! • This one!

13. Graphic Organizer (WRITE THIS!) THEN… ENERGY changes IF… IF… WORK Is done THEN… W = ΔE

14. Graphic Organizer (WRITE THIS!) ∑E = PE + KE THEN… ENERGY changes IF… IF… WORK Is done THEN… W = ΔE

15. Graphic Organizer (WRITE THIS!) ∑E = PE + KE THEN… ENERGY changes IF… IF… WORK Is done THEN… Mechanical Energy (M.E) Potential Energy (P.E) Kinetic Energy (K.E) W = ΔE

16. In addition to… • Work Energy Theorem • And the different types of PE & KE • The other main point for today is…

17. Law of Conservation of Energy Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes. Ch07 - Energy - Revised: 2/21/10

18. Conservation of Energy Example: Energy transforms without net loss or net gain in the operation of a pile driver. Ch07 - Energy - Revised: 2/21/10

19. Conservation of Energy Part of the PE of the wound spring changes into KE. The remaining PE goes into heating the machinery and the surroundings due to friction. No energy is lost.

20. Conservation of Energy Everywhere along the path of the pendulum bob, the sum of PE and KE is the same. Because of the work done against friction, this energy will eventually be transformed into heat.

21. Do #1-9!

22. P.E P.E P.E P.E P.E

23. K.E K.E K.E K.E

24. Finish up to & INCLUDING HERE today (#5 on the last sheet of paper)(anything not finished is HW)

25. EXIT SLIP – on scrap ID: NAME: DATE: CLASS: • Is it possible for an object to have both PE & KE simultaneously? EXPLAIN • What did you learn today that you are REALLY confident about? • What is confusing you?