4. Work in life

5. Work in physics

6. “WORK”

7. Formula: W=F( s)cos0 or
W=Fd

8. Example of work is when your exerting a great
force in pushing an box to move it to the other
side of the room. That’s work

9. Types of work

10. Work against inertia

11. Example:
if you throw a ball, the work done consists of the distance
you accelerated the ball until you let it go. Once you have
thrown the ball, it will continue at a constant velocity and no
further work is done.

12. Work against gravity

13. When your lifting a book,
you’re working against gravity

14. Work against friction

15. If you pushed a box across a slippery floor,
it might continue to slide for a short
distance after you stopped pushing.

16. -is a derived unit of energy, work, or
amount of heat in the International
System of Units.
- This SI unit is named after James
Prescott Joule. As with every
International System of Units (SI)
unit whose name is derived from the
proper name of a person, the first
letter of its symbol is upper case (J). James Joule – Physicist

19. James Watt

29. As an object fall, its PE decreases while its KE
increases, or if its rising the PE increases
while KE decreases.

31. •Imagine that you are on a swing.
think about the changes of energy
when you are swinging.
at what point do you have the max
PE and Max KE energy?
and what happens to the
Mechanical energy as you swing?

33. •Energycannot be created or
destroyed
•Theenergy of the universe
remains constant

34. •Remember the swing?...what if you stop swinging?
= if you stop swinging you need to remember
friction, as you slow down on the swing the chain
rubs against each other.
•Plusthe rubbing of the metal chains in a swing
make the metals temperature heated.
Which means that energy is still there its just
that its in a different form.

38. The change in the kinetic energy
of an object is equal to the net
work done on the object.

39. Example: Work-energy theorem
Question
A 1 kg brick is dropped from a height of 10 m. Calculate the
work done on the brick when it hits the ground assuming that
there is no air resistance.
Answer
Determine what is given and what is required
•Mass of the brick: m=1 kg.
•Initial height of the brick: hi=10 m.
•Final height of the brick: hf=0 m.
•We are required to determine the work done on the brick as
it hits the ground.

40. Determine the brick's potential energy at hi
PE=m·g·h=(1 kg)(9.8 m/s²)(10 m)=98 J
Determine the work done on the brick
The brick had 98 J of potential energy when it was released
and 0 J of kinetic energy. When the brick hit the ground, it
had 0 J of potential energy and 98 J of kinetic energy.
Therefore KEi=0 J and KEf=98 J.
From the work-energy theorem:
W=ΔKE=KEf−KEi=98 J−0 J=98 J
Hence, 98 J of work was done on the brick.

42. The gravitational force has an interesting
property that when an object is moved from one
place to another, the work done by the
gravitational force does not depend on the choice
of path.
Forces like these are called conservative forces.

43. A force is conservative when the work it
does on a moving object is independent
of the path between the object's initial
and final positions.

44. A force is non-conservative when the work
it does on a moving object is dependent of
the path between the object's initial and
final positions.

45. Conservative Forces Non-conservative Forces
Gravitational force Static and kinetic
frictional forces
Elastic spring force
Air resistance
Electric force
Tension
Normal force
Propulsion force of a
rocket

47. The total mechanical energy (E = KE + PE) of an
object remains constant as the object moves,
provided that the net work done by external
non-conservative forces is zero.

51. In the roller coaster example, we ignored non-conservative
forces, such as friction. In reality, however, such forces
are present when the roller coaster descends. The actual
speed of the riders at the bottom is 41.0 m/s. Assuming
again that the coaster has a speed of 3.0 m/s at the top,
find the work done by non-conservative forces on a 55.0-
kg rider during the descent.

52. Work Energy Power
refers to an activity is the capacity for doing is the rate of doing
involving a force and work. You must have work or the rate of
movement in the energy to accomplish using energy, which are
directon of the force. A work - it is like the numerically the same. If
force of 20 newtons "currency" for you do 100 joules of
pushing an object 5 performing work. To do work in one second
meters in the direction 100 joules of work, you (using 100 joules of
of the force does 100 must expend 100 joules energy), the power is
joules of work. of energy. 100 watts.

53. Units
Quantity Symbol Unit S.I. Units Direction
velocity v→ — m·s−1 or m·s−1 ✓
momentum p→ — kg·m·s−1 or kg·m·s−1 ✓
energy E J kg·m2·s−2 or kg·m2·s−2 —
Work W J N·m or kg·m2·s−2 —
Kinetic
EK J N·m or kg·m2·s−2 —
Energy
Potential
EP J N·m or kg·m2·s−2 —
Energy
Mechanical
U J N·m or kg·m2·s−2 —
Energy
Power P W N·m·s−1 or kg·m2·s−3 —
Table 1

55. You don't always get what you wish
for, you get what you work for.

56. http://www.school-for-champions.com/science/work.htm
http://library.thinkquest.org/2745/data/ke.htm
http://www.regentsprep.org/Regents/physics/phys02/rolcoast/default.htm
http://www.discoveryeducation.com/teachers/free-lesson-plans/elements-of-
physics-energy-and-work.cfm
http://www.sparknotes.com/physics/workenergypower/workpower/section2.rhtml
http://everythingscience.co.za/grade-12/08-work-energy-and-power/08-work-
energy-and-power-03.cnxmlplus
http://hyperphysics.phy-astr.gsu.edu/hbase/work.html