Transcript Ch 5 & 6 Powerpoint - Taylor County Schools

No work is done
Work is done
In science and
technology
work is done
when a force
acts on a body
and the body
moves in the
direction of the
force.
Work = Force x Distance
OR
W=Fxd
If you don’t move the object,
no work is done!!!!!!!!!!!!!!
Is work being done?
Is work being done?
The SI unit for both work and
energy is the joule.
1 Joule = 1Newton x 1 meter
OR
J=Nxm
Power – The rate at
which work is done
Power can be defined
as:
Power = Work
Time
P = w/t
Energy is the
ability to do
work!
The SI unit for
energy is the
joule.
There are several types of
energy:
 Potential
 Kinetic
 Chemical
 Nuclear
 Radiant (Heat)
Mechanical Energy Energy due to the
position of
something or the
movement of
something.
It can be in the form of
kinetic or potential
energy or the sum of
both.
ME = KE + PE
Potential Energy
Stored energy
(ex: stretched
spring, drawn
bow, coal).
There are several
types of potential
energy:
1) Elastic potential
energy
2) Chemical potential
energy
3) Gravitational
potential energy is
due to an objects
elevated position.
Gravitational potential
energy can be
calculated using the
formula:
GPE = mgh
Where m = mass, g =
the gravitational
constant of 9.8m/s2,
and h = the height of
the object.
Kinetic energy
is energy of
motion. All
moving
objects have
kinetic
energy.
KE = ½ mv2
Law of
conservation
of energy –
Energy cannot
be created or
destroyed. It
can only be
transformed
into another
form of energy.
A machine is a
device that
multiplies and
changes the
direction of
the force.
Machines make work
easier by:
1) increasing the force
that can be applied to
an object
2) Increasing the
distance over which a
force can be applied
3) Changing the direction
of force
The most basic
machines of all are
called simple
machines.
There are six types of
simple machines that
are divided into two
families, the lever
family and the inclined
plane family.
Lever – all levers
have a fulcrum
(pivot point).
There are three
types of levers.
• 1st class lever
• 2nd class lever
• 3rd class lever
1st class lever –
fulcrum is in the
middle, the input
force acts on one
end and the other
end applies an
output force
(hammer, sea-saw)
The fulcrum is in the
middle.
2nd class lever –
fulcrum is at one
end of the arm
and the input
force is applied to
the other end
(wheelbarrow,
hinged doors)
The output is in the
middle.
3rd class lever –
multiplies
distance
instead of force
(human joints –
elbow, knee)
The input is in the
middle.
Pulley – used to lift
things. Using
more than one
pulley or movable
pulleys increase
efficiency.
Fixed Pulley – The pulley
is attached to
something that does
not move.
Moveable Pulley – One
end of the wheel is
fixed and the pulley is
free to move.
Multiple pulleys are
sometimes called
a block and
tackle.
Wheel and Axle – is
made of a lever
or a pulley (the
wheel)
connected to a
shaft (the axle).
When a small input
force is applied to
the axle, the force is
multiplied to become
a large output force
applied to the wheel
(steering wheel,
screwdriver).
Inclined Plane
(Ramp) – turns a
small input force
into a large
output force by
spreading the
work out over a
large distance.
Wedge – two inclined
planes back to back, it
turns a single
downward force into
two forces directed
out to the sides (wood
splitter, nails).
Screw – is an inclined
plane wrapped
around a cylinder, it
requires a small
force acting over a
large distance (jar
lids, spiral
staircase).
A machine that
combines two or
more simple
machines is called
a compound
machine.
Mechanical Advantage=input distance
output distance
Mechanical Advantage= Output Force
Input Force
Mechanical Advantage:
A machine with a mechanical advantage of 1
or greater multiplies the input force
A machine with a mechanical advantage of
less than 1 does not multiply the input
force but it does increase the distance
and/or speed.
What is efficiency?
Efficiency is a measure of how much of the
work put into a machine is changed into
useful output work.
Calculated using the following formula:
Efficiency % = output work (J) x 100%
input work (J)