Transcript work - ruthedradan

WORK AND ENERGY
Presentors:
 Modanza, Kent Noreen G.
 Garrido, Nurissa M.
 Sanchez, Ellen Jane A.
 Buray, Leri Maree Axela C.
 Olvis, Hazel Lynn S.
 Caduan, Joereth Anne P.
WorkIn physics, work is a scalar quantity that
can be described as the product of a force
times the distance through which it acts, and
it is called the work of the force.
The term work was first coined in 1826 by
the French mathematician Gaspard-Gustave
Coriolis.
ForceIn physics, a force is any influence that
causes an object to undergo a change in
speed, a change in direction, or a change in
shape. Force can also be described by
intuitive concepts such as a push or pull.
A force has both: magnitude and direction….
making it a vector quantity.
MotionIn physics, motion is a change in position of an object
with respect to time. Change in action is the result of an
unbalanced force.
PowerIn physics, power is the rate at which energy is
transferred, used, or transformed. For example, the
rate at which a light bulb transforms electrical
energy into heat and light is measured in watts—the
more wattage, the more power, or equivalently the
more electrical energy is used per unit time.
Work is the use of force to
move an object
Work = (F) (d)
Force is necessary to do work.
Joule is the unit for
work
Work depends on force
and distance
• WORK involves the application of a
force over a distance.
• Therefore, we measure work in terms
of a:
• FORCE (F) acting over a straight line
and DISTANCE (d).
• W=F(d)
Mathematically,
W=F(cos ᶿ) d
Where F= force, d= displacement, and the angle
(theta) is defined as:
-the angle between the force and the
displacement vector, which means it is not just any
angle, but rather a very specific angle.
There are three key words in this definition-
force, displacement, and cause.
In order for a force to qualify as having
done work on an object, there must be a
displacement and the force must cause the
displacement. In other words..in this
case…if there is no force or displacement,
no work.
The standard metric unit for work (and also energy) is the joule
(abbreviated “J”). One joule is equivalent to one newton of force
causing a displacement of one meter. In other words:
1 Joule = 1 newton * 1 meter
1J=1N*m
Non-standard units of work include the following:
ft-pound
kg*m/s 2 *m
kg*m2/s2
Notice that when analyzed, each set of units is equivalent to a force
unit times a displacement unit.
Summary:
 Work is a force acting upon an object to cause a
displacement.
 Three quantities must be known in order to calculate
the amount of work. These are: force, displacement
and the angle between the force and the displacement.
Problem 1:
Work or No Work??
Click me!!!
F = 10 N
1 meter
The force, a push along the ground (10 N), and
the distance moved by the crate (1 meter) are
in the same direction, so work (10 joules) has
been done.
W
= F * cos ᶿ * d
= 10 N * cos 0° * 1 m
= 10 Joules
since cos 0°
=1
SO, WORK IS DONE.
Force is necessary to do work.
Most people say they are working when they do
anything that requires a physical or mental effort. In
scientific terms, you do work only when you exert a force
on an object and move it. According to this definition of
work, reading this page is not doing work. Turning the
page, however, would be work because you are lifting
the page.
What if I just read my book? IS there any
work done?
YES and NO.
(Kindly listen to the explanation of the
reporters……)
Click me!!!
Force is a vector. This is just like getting the –
component of the vector, where the x-axis
represents the displacement.
F
ᶿ
displacement
is important because even if there is force and displacement on a
ᶿ
body, the angle ᶿ will also determine whether there is work, maximum
work or zero work.
Maximum work
We can get the maximum possible work if
cos 0° = 1.
ᶿ
ᶿ =0°,
=0°
F
displacement
Work is maximized when the force applied is
completely along the direction of the
displacement. There are no other components
that would reduce the value of force.
W = Fd
Zero work
Let us take a look at the formula again.
W= F(cos ᶿ ) d
When will W be zero if F and d are non-zero? When cos
ᶿ = 0. This will only be zero if ᶿ = 90°, so
F
ᶿ
=90°
displacement
The angle between the force and the displacement is
90°
Work done against Gravity
The work needed to lift an object of mass m
against gravity is easy. The force of gravity on the
object is simply its weight w = mg. That will be our F.
Our displacement is simply the height to which the
object is raised.
W
=F
= mg
x
x
d
h
So, to lift an object of mass m to the height H requires
the work mgh.
Force, Motion, and Work
Work is done only when an object that is being pushed or pulled
actually moves. If you lift a book, you exert a force and do work. What if you
simply hold the book in front of you?
Work is done only by the part of the applied force that acts in
the same direction as the motion of an object. Suppose you need to pull a heavy
suitcase on wheels. You pull the handle up at an angle as you pull the suitcase
forward. Only the part of the force pulling the suitcase forward is doing work.
…(The force with which you pull upward on the handle is not doing work
because the suitcase is not moving upward-unless you are going uphill.)
*Give two examples of when you are applying a force but not doing work.
WORK CHANGES POTENTIAL AND KINETIC ENERGY.
When you throw a ball, you transfer energy to it and it
moves. By doing work on the ball, you can give it
kinetic energy (kuh-NEHT-ihk).
When you do work to lift a ball from the ground, you
give the ball a different type of energy, called potential
energy. (kindly listen to the reporter’s explanation…)
You can also give some objects potential energy by
changing their shape. (example: spring. Explain)
KEY CONCEPTS
1. If you push very hard on an object but does not move,
have you done work? Explain.
2. What two factors do you need to know to calculate
how much work was done in any situation?
3. Was work done on a book that fell from a desk to the
floor? If so, what force was involved?
CRITICAL THINKING
4. Synthesize Work is done on a ball when a soccer player
kicks it. Is the player still doing work on the ball as it
rolls across the ground? Explain.
5. Calculate Tina lifted a box 0.5 m. The box weighed 25N.
How much work did Tina do on the box?
Power is the time rate at which work is done or energy is transferred. In
calculus terms, power is derivative of work with respect to time.
The SI unit of power is the watt (W) or joule per second (J/s).
Horsepower is a unit of power in the British system of measurement
.
Velocity, Acceleration, Momentum, Force
QUESTIONS
1. Describe work.
2. W= f x d. What is meant by f, and d?
3. 1 J=1 Nm (newton meter). What does Newton meter signify?
4. Work can be done against gravity. In normal circumstances, W = F x d. What will
be the formula be if work is done against gravity?
5. Relate the relationship of force, displacement and motion.
6. Define energy . 4 or 5 words will be the limit. No more, no less.
7. Give the three types of kinetic energy.
8. You have learned the acronym VAMF. Enumerate the four words in this acronym.
9 – 10. Kinetic energy depends on two variables/ quantities. Enumerate the two. tp
HINT: ONE IS THE MASS OF ANN OBJECT. It will be up to you to add the other one.
1. A big box of watermelons (30 kgs) is
lifted from the ground to the top shelf
of the freezer. If the box is lifted at a
constant speed, a distance of 1.75 m,
what work is done if it is against
gravity?
2. A 20 kg sled is pulled p a 10 m tall
hill. What work is done if it is against
gravity?
3. FORMULA: MG X H
humaNA MO???/
Naa pai dugang. =D
• CALCULATE THE WORK DONE BY
A 50 N FORCE PUSHING A BOX
ACROSS A 10 M DISTANCE.
•5 POINTS TUN;……PAGANSWER
RA LAMANG….
ANSWERS:
1. Work is a scalar quantity that can be described as the product of force times
distance.
2. f is force; d is distance
3. A force of 1 newton causing a displacement of 1 meter.