1. What do you think of when
you hear the words:
Energy, Work & Power?

2. Energy Universe is made up of matter and energy.
Energy is the mover of matter.
Energy has several forms:
Kinetic
Potential
Electrical
Heat
etc.

3. Conversions from one form of energy to another continually occur.
Energy cannot be created or destroyed.

5. Work = Force|| x Distance
In this case, the distance is the magnitude of the displacement.
Only the component of force parallel to the displacement does work

6. Work Force applied in the direction of motion
Work = Force|| ´ Distance
W = F||d
The unit for work is the Newton-meter which is also called a Joule.
1 joule is equal to a force of 1 N exerted over a distance of 1 m

7. x

8. Work or No Work

9. m= 10kg
In this case, the weight does positive work
d = 2 m
Work = mgd = (100N)(2m)
Work = 200 Nm =200J
m= 10kg
mg = 100N

10. FA Fa m= 10kg In this case, the weight does negative work mg = 100N
d = 2 m Fa
Work = -mgd = -(100N)(2m)
Work = -200 Nm = -200J
m= 10kg
mg = 100N

11. Power measured in watts (W)
One watt of power is expended when one joule of work is done in one second.

12. Power Power is equal to the amount of work done per unit time.
The unit for power is the Joule/second which is also called a Watt.

13. What is horsepower? 1 horsepower = 746 Watts
A horse exerting 1 horsepower can raise pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute.

14. Mechanical Energy Em = Ek + Ep
Energy possessed by an object due to its motion or its stored energy of position.
It can either be potential energy or kinetic energy.
All forms of energy are measured in joules (J).
Em = Ek + Ep

15. Conservation of Energy
Energy cannot be created nor destroyed; it may be transformed from one form into another, but the total amount of energy never changes.
So why worry about conserving energy?

16. Conservation of Mechanical Energy
Ek (before) + Ep (before) = Ek (after) + Ep (after)
When no other type of energy is present.
Why does a dropped ball not return to its original elevation?

17. Energy Transformation of a Pendulum

18. Potential Energy (PE) stored chemical energy or energy of position.
An object’s ability (potential) to do work by virtue of its position.
Types: elastic, gravitational and chemical.
Examples:
Rubber bands
Springs
Bows
Batteries
Gravity?

19. Gravitational Potential Energy
PE = Weight ´ height
PE = m g h
Question:
How much potential energy does a 10kg mass have relative to the ground if it is 5 meter above the ground?

20. Potential Energy
The same work is done on each block.  What matters is the final elevation, not the path followed

21. Kinetic Energy Ek = ½ mv² The energy of motion.
Kinetic Energy = ½ mass ´ velocity2
Ek = ½ mv²

22. How much work does gravity do on the falling mass?
PE = mgh mg h h
Work = mgh mg

23. How much energy does the mass have at the bottom of its fall, just before it hits the ground?
PE = mgh mg h h
Kinetic energy mg v

24. PE = mgh
If potential energy at top of path is 100 J, how much kinetic energy does the ball have just before it hits the ground and comes to a stop? mg h
KE = ½ mv2 mg v

25. Object Falling from Rest

26. Practice:
Think about standing on your desk…if you jumped off, how fast would you be moving just prior to reaching the floor?
How much work would you do on the floor? (Refer back to previous slide if needed)

27. More Practice
Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s.
If the roller coaster car doubled its speed, what would be its new kinetic energy?

28. Calculate speed at positions B,C and D.

29. More Energy Transfer
High speed winds are used to do work on the blades of a turbine at the so-called wind farm.
Mech. Energy from the air gives the air particles the ability to apply a force to the blades.
As the blades spin, their energy is subsequently converted into electrical energy (a non- mechanical form of energy) and supplied to homes and industries in order to run electrical appliances.

30. Energy Transfer...
This diagram shows that the potential energy of the boy is changing as he swings. Explain what is happening, in other words how is the energy changing?

31. Work/Energy Relationship
If you want to move something, you have to do work.
The work done is equal (ideally) to the change in kinetic energy.
what is ideal? is this actual?
W = DKE

32. Work-Energy Relationship
What happens to your stopping distance when you…
Double your speed?
Triple your speed?

33. Joule to Joule

34. Forces in Car Crashes

35. Seatbelt Physics

36. The formula for KE is _____?
Kinetic Energy is dependent upon ___ & ____
If an object’s velocity doubles, its kinetic energy _____. If velocity triples, it will have _____ times the kinetic energy.
If mass doubles, kinetic energy _____. If mass triples, kinetic energy _____.
…so what happens to KE if mass doubles and velocity doubles? What if mass is cut in half and velocity doubles?

37. Bungee Jumping
You wish to bungee jump off of a platform. Assuming that there is no air resistance and the spring constant of the 40 m long bungee cord is 100 N/m. How high should your platform be?
Determine all the forces acting ON the body.
Draw a free body diagram.
Apply Newton's second law.
Think about elastic potential energy.
Solve.

38. Tennis Ball Bounce

39. Relative “bounciness” of various types of balls
Elasticity of an object
tendency of the object to return to its equilibrium (natural ) shape natural shape when Fnet =0
Restoring Force
the force required to return object to its equilibrium shape is called the restoring force – it is always directed opposite to the deformation of the object.
Relative “bounciness” of various types of balls