Work is done when a force causes an object to be displaced in the same direction. It can be calculated as the product of the force magnitude and displacement magnitude. Kinetic energy is the energy of a moving object and depends on its mass and velocity. The net work done on an object equals the change in its kinetic energy. Potential energy is stored energy due to an object's position or state of deformation. It depends on mass, height, and elastic properties. Power is the rate at which work is done or energy is used and can be calculated as work over time or energy over time.

1. Work, Energy, and Power
Forces in doing work, rate of doing work, and in
energy transformation

2. Work
defined as the product of the force magnitude F
and the displacement magnitude d

3. Work is done Work is done
Work is done
displacement
displacement

4. No work is done

5. No work is done

6. + Work is done by the man
+ Work is done by gravity
lifting
falling

7. Work
Is done when the Force (Fnet) applied to an
object causes that object to be displaced (d)
in the same direction as the force applied.
Is a method of transferring energy

8. How can we
The ground is doing
+ work on us.
http://2.bp.blogspot.com/-EsjHgHyE0Xo/VU-Mz9UejGI/AAAAAAAALq4/MOdF14vdUv8/s1600/walk1.jpg

9. Work
𝑊 = 𝐹𝑑𝑐𝑜𝑠𝜃

10. Example
Suppose a woman is pushing a grocery cart with a
500 Newton force along the 7 meter aisle, how much
work is done in pushing the cart from one of the aisle
to the other?
http://www.google.com.ph/imgres?imgurl=http://vectortoons.com/wp-content/uploads/2015/02/shopping-collection-sarah-004.jpg&imgrefurl=http://vectortoons.com/product/a-woman-pushing-a-shopping-cart-
inside-the-supermarket/&h=904&w=1024&tbnid=lU4J2cTaNdNsnM:&zoom=1&docid=i94W7CJRHFiiOM&ei=4IN1VbmxJ5H3oAT-v4OwCQ&tbm=isch&ved=0CC4QMygqMCo4ZA

11. Example
The librarian found a book of mass 1kg is on the floor.
If the book is lifted by the librarian from the floor to the
top shelf which is 2 meters from the floor, how much
work is done on the book?
http://bloximages.chicago2.vip.townnews.com/nwitimes.com/content/tncms/assets/v3/editori
al/9/bb/9bbd9852-8a43-5056-8293-3e2c919deff5/506d0316cf7a7.preview-620.jpg

12. Kinetic Energy (KE)
Is the energy of a moving object
Quantifies the amount of work an object can do
because of its motion

13. Kinetic Energy (KE)
𝐾𝐸 =
1
2
𝑚𝑣2

14. Work-energy principle
The net work done on an object is equal to the
change in the objects kinetic energy.
𝑊 = 𝐾𝐸𝑓 − 𝐾𝐸𝑖 = ∆𝐾𝐸

15. Example
A 1000kg jeepney has a velocity of
17 m/s. What is its kinetic energy?
A 2000kg jeepney has a velocity of
17 m/s. What is its kinetic energy?
A 1000kg jeepney has a velocity of
34 m/s. What is its kinetic energy?
http://www.paulancheta.com/weblog/images/07-04-
2-jeepney.jpg

16. Example
A 145-g baseball is thrown so that
it acquires a speed of 25m/s. a)
What is its KE? b) What was the
net work done on the ball to make
it reach this speed, if it started from
rest?
http://www.nextlevelballplayer.com/wp-content/uploads/2012/10/baseball-hitting-tips.jpeg

17. Example
How much net work is
required to accelerate a
1000kg car from 20m/s to
30m/s?
http://www.gannett-cdn.com/-mm-/79af5a7336b66a51e8927d539cedabfd7085a349/c=72-0-1209-853&r=x404&c=534x401/local/-
/media/2015/05/14/DetroitNews/B99270515Z.1_20150514165000_000_G47GNCQ1.1-0.jpg

18. Potential Energy
Is energy gained in raising an object from the ground
or lost when made to fall
Also known as gravitational potential energy

19. Potential Energy
𝑃𝐸 = 𝑚𝑔ℎ

20. Highest PE PE decreases as KE increases
http://scienceblogs.com/startswithabang/files/2011/12/kinetic_energy_c_la_784.jpeg

21. Example
What is the potential energy of a 1
kg book lifted to a 0.5m height
above a table?
What is the potential energy of a 1
kg book lifted to a 1.5m height
above a table? http://etc.usf.edu/clipart/63200/63282/63282_books_table_lg.gif

22. Elastic Potential Energy
depends on an elastic material’s elasticity and
how much the material is stretched or
compressed
http://images.wisegeek.com/spring.jpg

23. Elastic Potential Energy
𝐸𝑃𝐸 =
1
2
𝑘𝑥2

24. Rest position EPE stored Work done to
release
energy

25. Power
rate of doing work or the rate of using energy
𝑃 =
𝑤𝑜𝑟𝑘
𝑡𝑖𝑚𝑒
=
𝑒𝑛𝑒𝑟𝑔𝑦
𝑡𝑖𝑚𝑒

26. Power
rate of doing work or the rate of using energy
𝑃 =
1 𝐽𝑜𝑢𝑙𝑒
1 𝑠𝑒𝑐𝑜𝑛𝑑
= 1Watt

27. Example
A 50.0kg marathon runner runs up the
stairs to the top of the approximately
350m-tall MSHS building. To lift herself
to the top in 15.0minutes, what must be
her average power output?

28. Mechanical Energy
∆𝐾𝐸 + ∆𝑃𝐸 = 0
𝐾𝐸2 − 𝐾𝐸1 + 𝑃𝐸2 − 𝑃𝐸1 = 0
𝐾𝐸2 + 𝑃𝐸2 = 𝐾𝐸1 + 𝑃𝐸1

29. Example
A 50 kg member of your group jumped straight
up in the air with an initial speed of 2.94 m/s.
Ignoring air resistance, a) how high (in m) did he
go? b) What is the amount of work done? c)
How much force was exerted by the floor on that
member?

30. Example
c) How much force was exerted by the floor on
that member? d) how long (in sec) did it take the
member to reach that height? e) what is the
power of this member of your group?

32. http://www.daviddarling.info/images/hydroelectric_power_plant.gif