Transcript Work&Machines

Work &
Machines
What is work?
• If you push or pull something, that is
NOT work.
• Work is the transfer of energy that
happens when a force makes an object
move.
• Remember – force is a push or a pull
on an object
• Key - for work to be done, the object
has to move.
Doing Work
• Two things have to happen in
order to consider it work…
1. The object has to move
2. The motion of the object has to be
in the direction the force was
applied.
Doing Work Example
•
•
The bell rings and you need the
books under your desk.
Lifting up the book is doing
work…why?
1. The books move and…
2. There is a force applied, by your arms,
in the direction that the books move.
Doing Work Example
• Your arms are doing the work.
• Now that they are in your hands, you
start to walk with them…
• It is now your legs that are doing the
work to move you and your books, not
your arms.
Work and Energy
• When work is done, energy is always
transferred.
• Think about carrying a box with your
kid brother up the stairs. When you
are done, your arms will be sore.
• Remember – when you increase the
height of an object you increase its
potential energy.
Work and Energy
• So, by taking the box-n-brother up the
stairs, you have increased its height,
therefore, increasing its potential
energy and you transferred energy to it.
Work and Energy
• Remember – Energy is the ability to
cause change.
• AKA – Energy is the ability to do
work.
• If something has energy, it can
transfer energy to something else.
Work and Energy
• When you do work on something, you
increase its energy.
• IF you do work on something, you
decrease your energy.
• Energy is always transferred from the
object that is doing the work to the
object that has the work done on it.
Calculating Work
• Would you do more work if you lifted
the books from the floor to your waist
or from the floor to over your head?
• Over your head…
• You do more work when you exert a
greater force and when you move an
object a greater distance.
Calculating Work
• The amount of work done depends
on two things.
1. The amount of force exerted
2. The distance the object is
moved
Calculating Work
• When a force is exerted and an object
moves in the direction of the force, the
amount of work done can be calculated…
• Work = Force x distance
• W=Fd
Calculating Work
• If Maria applies a
force of 25N to a
baseball for a
distance of .1m,
how much work did
she do?
• W=?
• F = 25N
• d = .1 m
•W=Fxd
•W = 25 N x .1m
•W = 2.5 J
Remember Newton x meter =
Joule
&
Work is always
measured in Joules
Calculating Work
• Force is measured in
– Newtons (N)
• distance is measured in
– meters (m)
• Newton (N) times meters (m) = Joule
• Work, like energy is measured in
– Joules (J)
• One joule is about the amount of work
required to lift a baseball a vertical
distance of 0.7m
When is work done?
• Push a book across a table a distance of
1m.
• The distance you use to calculate the
work you did is how far the book moved
while the force is being applied, or
while your hand is in touching the book.
• The distance in the formula, W=Fd, is
the distance that your hand was in
contact with the book