A serious slide show on Force and Motion mainly for non-science experienced elementary teachers.

1. TO SEE THE BUILT- IN ANNIMATION EFFECTS, THIS SLIDE SHOW MUST BE DOWNLOADED

2. Force
Force is a push or a pull
and
Motion
By Moira Whitehouse PhD

3. The strength of a force can be measured. How strong
the push or pull is measured with a spring scale in
units called newtons.
One newton is equal to about a quarter
of a pound.
This is a newton scale. By hooking it
onto an object and pulling it along, one
can read the force that is required to
move that object under those conditions.

4. There are four kinds of forces; some scientists
also add the fifth, friction.
Strong nuclearforce responsible for binding atomic
Short-range force:
nuclei together. The strongest of the four
fundamental forces of nature.
Important force in certain decaying functions
Weak nuclear force:
within the atom, but way beyond me.
Electromagnetic force: a force between objects
exerted by positively and negatively charged
particles.
Gravitational force: the force of attraction
between all masses in the universe; especially the
attraction of the earth's mass for bodies near it.

5. Electromagnetic force
We know that everything is made up
of tiny particles called atoms.
Let’s start with....
Although atoms are much too small to
be seen, scientists have figured out
that they are made of even smaller
particles that have electrical charges.
They are called protons and electrons.

6. Protons and electrons
Everything is made up of atoms and every atom is
made up of protons in the nucleus with positive
electrical charge (+) and electrons swirling around
the nucleus each with a negative electrical charge
(-). There are also neutrons in the nucleus but they
have no electrical charge.
http://www.windows.ucar.edu/

7. Because atoms have the same number of
positive (+) and negative (-) charges, most
things are in electrical balance.
But when the
atoms of an
object get out
of balance
electrically, stra
nge things
happen.

8. They can get out of balance when the swirling
negatively charged electrons are knocked loose from
their atom. This can happen rather easily and helps
explain static electricity.
Sometimes when two electrically balanced objects
rub against each other, electrons from the one are
rubbed off onto the other. The object that received
the electrons would then have extra electrons and an
overall negative charge.
The object that lost the electrons would no longer be
balanced having too many protons for the remaining
electrons and thus becoming positively charged.

9. Even though we say that “strange things” happen
depending on the balance or unbalance status of the
electrons, the reactions are actually very predictable.
If the both objects have excess negative charges:
If the both objects have excess positive charges:
If the objects are balanced: and the other has
If one object has positive
negative excesses:
Opposite charges
Uncharged attract
Like charges
repel

10. Shoes and carpet, like most everything else, are
made of atoms that are electrically balanced. But
when shoes rub against the carpet, electrons are
transferred from the carpet to the shoes and the
shoes become negatively charged.
The carpet which loses electrons to the shoes
becomes positively charged.

11. As you proceed about your business with all those
extra electrons, you do not notice anything until......
you touch a metal doorknob?
Those electrons that
moved up from your
shoes are now ready to
get “in balance” again.
The metal doorknob
ZAP!!! which is a good conductor
of electricity, is neither
positively or negatively charged. When your
negatively charged finger approaches the metal
doorknob the attraction becomes greater until...

12. You may have noticed that you do not build up
static electricity when you walk across a concrete
floor. That is because some atoms hold on to
their electrons more tightly than others do.
Examples of materials that are more apt to
give up electrons are: fur, glass, human
hair, nylon, wool, silk.
Examples of materials that are more apt to
capture electrons are: styrofoam, Saran
Wrap, polyurethane polyethylene (like
Scotch Tape) polypropylene vinyl (PVC).

13. Often when you take clothes from the
clothes dryer, they seem to stick together.
This is because some of the clothes have
gained electrons by rubbing against other
clothing. The clothes losing electrons
become positive and are then attracting
those pieces of clothing that have gained
extra electrons. Or, negative
clothes are attracted to the positive
clothes.

14. The bottom line, once again:
Objects with + and –
charges attract one
another.
Objects with extra (-)
charges push away away
from each other.
Objects with extra (+)
charges push away
away from each other.

15. It’s like the poles of a magnet,
“likes repel and opposites attract.”

16. Now we will do an experiment to
demonstrate what we have been
discussing.

17. Here we have two pieces of tape with the ends
wrapped around tooth picks.
These two pieces of tape are marked with a “B”
to show that they are on the bottom and
sticking to the surface.
B B

18. Next we will stick two more pieces of tape on
top of the first two. They are marked with a
“T” for top.
B
T
B
T

19. Using your materials, set up the experiment by
sticking (pressing) your “T” tape directly over
the (on top of) the “B” tape while it is still
sticking to the surface of your table.
Now peel the top tapes off. They both had
B
electrons stripped away when they were
B
peeled up. T
T
So now the “T” tapes will have fewer electrons
because of those they lost, but the same
number of protons they started with, which
makes them positively (+) charged.

20. Now you are going to “test” your two “T” pieces
of tape by holding them close to each other to
see if they repel or attract. Before you do, make
a prediction.
Next, peel up the “B” pieces of tape from your
table and after making your prediction, test
them in the same way.
Finally, test one of the “B” pieces of tape with
one of the “T” pieces, but only after making a
prediction whether they will repel or attract.

21. Another vivid
demonstration
of what
happens when
the electric
balance of an
object is upset
is the Van de
Graff generator.

22. The Van De
Graff generator
is a device that
demonstrates
the effects of
unbalanced
charges as can
be clearly seen
here.

23. Van de Graff generators have several parts: a motor, a belt, two
rollers, two "combs," and a metal sphere. The bottom roller is
made out of a material that loses electrons easily, and the upper
out of a substances that readily captures electrons. As the
motor turns, the rubber belt first goes over the bottom roller.
A comb pulls electrons from the material on the bottom roller
(which loses electrons easily) and transfers them to the
rubber belt. The belt then travels to the top roller. The
second comb near the top roller collects the electrons from
the belt and stores them on the metal sphere. The
motor turns very fast, so the sphere quickly collects a
lot of electrons and becomes negatively charged and so
do you when you touch the dome.
Touching a charged sphere is truly a "shocking" experience!

24. When a person places their hand on the ball and the
machine is turned on, electrons are transferred to and
collected on the person touching the silver ball.
Why do you
think this
machine affects
the hair of the
children in the
picture?

25. Magnetism and electricity are related.
If you run electricity through a wire, a
magnetic field is set up around the
wire-- the wire becomes a magnet as
long as electrons flow through it.
Activity with circuit and compass.

26. An electromagnet is a magnet that runs on electricity.
An electromagnet works because an electric current
produces a magnetic field.
Unlike a permanent magnet, the strength of an
electromagnet can easily be changed by changing
the amount of electric current that flows through it.
The poles of an electromagnet can be reversed by
reversing the flow of electricity.
If a wire carrying an electric current is formed into a
series of loops, the magnetic field can be
concentrated within the loops. The magnetic field
can be strengthened even more by wrapping the
wire around a core of soft iron.

28. This business of an electric current running through a
coil of wire and making a magnet opens all sorts of
possibilities, like electric motors and electric
generators.
Any electric motor is all about magnets and
magnetism. A motor uses magnets to create motion.
We will use this simple
Beakman motor for
study. The armature
or rotor (in this case
the coil of copper wire)
is an electromagnet.

29. The ends of the copper wire in the coil make contact
with the pieces connected to the battery terminals.
Current flows through the coil, making it into an
electromagnet.
Since magnets attract, the coil is attracted to one pole
of the ceramic magnet.
Inertia causes the coil to continue around and when
the coil nearly completes a spin, the process repeats
itself.

30. Activity with electric motors

31. We have just seen how electricity is used to make
motion, now we’ll see how motion is used to make
electricity.
This is a generator.
It uses motion to
generate electricity.

32. A generator has As the shaft inside
a long, coiled the generator
wire on a shaft turns, an electric
surrounded by a current is
giant magnet. produced in the
wire.
When the
turbine An electric
turns, the shaft generator
and rotor also converts
turn. mechanical, movin
www.energyquest.ca.gov g energy into
electrical energy.

33. Consider the many things that we depend on daily that are
powered by electricity, and then realize our debt to its
discoverer. His name is Michael Faraday.
The generator is based on the principle of
"electromagnetic induction" discovered by Michael
Faraday, a British scientist in 1831 Mr. Faraday
discovered that if an electric conductor, like a copper
wire, is moved through a magnetic field, an electric
current will flow in the conductors.

34. Activity with generator

35. Next, we will examine the phenomenon
that keeps our feet on the ground:
Gravity

36. Gravity is a force.
Gravity is a force that pulls.
Every object has gravity.
So every object pulls on every other
object.
The more mass an object has, the harder
it pulls.

37. We will use two hypothetical planets for our
example. Both the blue and green planets
are pulling on each other.
Which one pulls harder?

38. This should help us see that the more mass
an object has the stronger its gravity.
Moon Earth
The Earth obviously has more mass than
But the Moon’s gravity is also pulling on
the Moon and it pulls harder.
the Earth. So hard that the oceans swell
So much harder that theever it passes. in an
toward the Moon where Moon is held We
call this high tide. Earth as though by some
orbit around the
magically strong string.

39. Let’s think about gravity on our favorite little
planet, Earth.

40. Gravity on Earth pulls everything toward
its center.

41. That’s why there is
no top or bottom
and no one falls
off.

42. If you dug a hole
right through the
Earth and fell
in, how far would
you fall?

43. You’d fall into the hole and shoot right past
the center because you would be going so
fast. As soon as you passed it, you
would be pulled
back towards the
center. So you
would bounce back
and forth like a
bungie jumper till
you finally stopped
at the center.

44. On Earth it appears that not everything falls
to the ground at the same rate.
It seems to us that things with less
mass or weight e.g. feathers fall
slower than things with more mass
or weight e.g. rocks.
This is a misconception.
As demonstrated by Galileo in the 1500’s, all
objects in a vacuum, fall at the same rate
regardless of mass.
Lighter objects on Earth fall slower due to
our atmosphere which slows their descent.

45. On the Moon, an astronaut dropped a
feather and a hammer.
Since there is no atmosphere on the
Moon the feather and the hammer hit
the ground at the same time.

46. Demo dropping book and paper.
1st Drop a book and wadded up paper at the same time. (land together)
2nd Drop a book with a sheet of paper touching the under side of the book. (land together)
3rd Drop a book with a sheet of paper touching the top of the book. (land together)
4th Drop a book and a sheet of paper separately but at the same time. (book lands before paper)
Use previous slides to explain why.

47. The weight of an object is a measure of
how hard gravity pulls on it.
However, the amount of gravity on each
planet differs. The Moon has only one-sixth
as much gravity as the earth.
Consequently, on the moon you would
weigh only one-sixth of what you weigh on
Earth.

48. This boy weighs
60 pounds on
Earth.

49. On the Moon he
would only weigh
10 pounds.

50. Since each planet has a
different amount of
gravity, this boy’s
weight would change
each time he went to
another planet.

55. On
Jupiter, this
would be like
carrying an
extra 100
pounds
around on
your back all
day.

56. The farther an object is from the center of
a planet, the weaker the force of gravity.
So, would this apple weigh more in some
place like Death Valley or on top of a very
high mountain?

57. Weight of a one pound apple heading out
to space.
Apple Apple Apple Apple
weighs weighs weighs weighs
1 pound 1/4 pound 1/9 pound 1/16 pound
here here here here

58. In a spaceship like the shuttle, you would be
weightless. However this is not because
you are so far from Earth that there is no
gravity. It is because the spaceship, being
pulled by gravity, is always falling from
beneath you.

59. Both of these men are weightless, still they are
both being pulled by gravity. They have weight
only when gravity pushes them against
something like the floor or a scale.

60. What causes gravity?
Even the great At his time
Sir Isaac Newton and still
couldn’t answer today, what
that one. causes gravity
is a mystery.
But it is a force that effects everything in
the universe.

61. Force
and
Motion

62. Motion is the process of an object moving.
An object’s motion changes when a force acts
upon it.

63. Newton’s Three Laws of Motion

64. Newton’s First Law of Motion--Inertia
• an object at rest stays at rest unless
acted on by another force
• an object in motion stays in motion
unless acted on by another force

65. Motion is a relative term.
All matter in the universe is moving all the
time, but the motion referred to in the first
law is a position change in relation to
surroundings.
We live on the Earth which is rapidly
rotating and orbiting the Sun. But when
we sit down we say we are at rest.

66. When you are sitting in your seat in an
airplane flying through the sky, you are
at rest.
But, if you get up and walk down the
airplanes aisle, you are in motion.

67. In order to understand the first law it
is important to understanding
balanced and unbalanced forces.
If you hold a ball in your hand and
keep it still, the ball is at rest.
All the time the ball is held there, it
is being acted upon by forces.
The force of gravity is trying to pull
the ball downward, while at the
same time your hand is pushing
against the ball to hold it up.
The forces acting on the ball are balanced.

68. Let the ball go, or move your hand upward,
and the forces become unbalanced.
The ball then changes from a state of
rest to a state of motion.

69. If you are not in
motion right
now, chances are
that you have
balanced forces
acting on you .

70. Now let’s get back to discussing the first
part of Newton 1st Law of Motion.
The first part of this law seems pretty
obvious—an object stays at rest until a
force acts upon it.

71. A ball sitting on
the ground is at
rest and when it
is rolling or
flying it is in
motion.

72. Furthermore, a
resting ball stays
resting until a force
acts upon it—in this
case a moving foot.

73. The second part of this law is less
obvious—an object in motion stays in
motion until a force acts upon it.
This is a difficult concept because in our
experience things do slow down and
stop, they don’t keep moving in a straight
line and at the same speed.
The reason, of course, is that there is a
force acting on those things. The force is
usually friction, which we will study later.

74. This second part
of the first law of
motion explains
why we should
wear seat belts.
The car and
person are both
in motion and
when the car
stops abruptly
the person stays
in motion flying
out of the car.

75. Astronauts who
“walk in space”
are tethered to
the shuttle or
space station so
they do not float
off into space.
Otherwise, when they push against the spacecraft, they
would start moving away from the ship and continue
moving out into space in a straight line until acted on by
another force.

76. Activity with car and clay: place a gob of clay on a
toy car, run the car into something fixed, car stops
clay flies forward. (inertia)
Activity: stack of pattern blocks (or poker chips) and a blade
with which to strike the bottom one. Bottom one flies
away, other stay (inertia).
Another: place an index card on a beaker or cup, place a penny
on index card then thump the card (card flies away, penny
drops straight down (inertia).

77. Newton’s First Law of Motion
combined with the Law of
Gravity explains why a planet
or moon orbits another (and
larger) object.
The planet or moon is actually
moving in a straight line that
would carry it away from the
larger object it is orbiting.
At the same time, the force of gravity pulls the planet or
moon towards the larger object.
As a result of the two balanced forces, the planet or
moon keeps falling into orbit around the larger object.

78. Newton’s Second Law of Motion
An object’s acceleration depends directly
upon the net force acting upon the
object, and inversely upon the mass of the
object.
As the force acting upon an object is
increased, the acceleration of the object
also increases.
As the mass of an object is increased, the
acceleration of the object decreases.

79. Acceleration is either a change in speed
(speeding up or slowing down) or a change
in direction.
Same speed, same
direction, this is not
acceleration. or slowing
Speeding up
down, is acceleration.
A change in direction is
acceleration

80. First:
An object’s acceleration is directly
proportional to the force. For
example, if you are pushing on an
object, causing it to accelerate, and
then you push, say, three times
harder, the acceleration will be
three times greater. If you push twice
as hard, it will accelerate twice as
much.

81. Second:
This acceleration is inversely proportional
to the mass of the object. For example, if
you are pushing equally on two objects, and
one of the objects has five times more mass
than the other, it will accelerate at one fifth
the acceleration of the other. If it gains
twice that mass it will accelerate half as
much.

82. Sometimes a picture can say more than
words. Let’s see.
We have a large force
and a small mass.
The large force is applied
to the small mass.
The small mass
accelerates
rapidly.

83. Or, in the other case:
We have a small force
and a large mass.
The small force is applied
to the large mass.
The large mass
accelerates
slowly.

84. A speeding bullet and a slow moving train
both have tremendous force. The force of the
bullet is a result of its incredible acceleration
while the force of the train comes from its
great mass.

85. A bowling ball has
a lot more mass
than a soccer ball.
If a bowling ball and a soccer ball were both
dropped at the same time from the roof of a tall
building obviously, because it has more
mass, the bowling ball would hit the ground
with greater force than the soccer ball.
We know that gravity accelerates all objects at
the same rate, so both balls would hit the
ground at the same time.

86. Therefore, the differences in force would
be caused by the different masses of the
two balls.
Newton stated this relationship in his
second law, the force of an object is
equal to its mass times its
acceleration.

87. Force 50 N If the mass
of an object
doubles, you
would need
to exert
Force 100 N twice the
force to
accelerate it
at the same
rate.

88. When you plug in the numbers for force in the Notice that doubling the force by adding
illustration above, (100 N) and mass (50 another dog would double the acceleration.
kg), you find that the acceleration is 2 m/s2. Oppositely, doubling the mass to 100 kg
would halve the acceleration to 2 m/s2.
Right granted for use for noncommercial use How Stuff Works

89. It is the force of
gravity that
causes an
object to move
down a ramp or
inclined plane.
The more mass an object has the greater the force of
gravity pulling on it even in this situation.
However, the acceleration of the objects be the same.
They will move down the ramp at the same rate
regardless of their mass.

90. Experiment to demonstrate Newton’s
Second Law of Motion (balls of
different masses)

91. Newton’s Third Law of Motion
For every action, there is an equal and
opposite reaction.

92. The rider
steps off the
skateboard.
In the Third Law, the stepping off the
skateboard is called the action.
The skateboard responds to that action by
traveling some distance in the opposite
direction. The skateboard's opposite
motion is called a reaction.

93. When you compare the distance traveled
by the rider and the skateboard are
compared, it appears as if the skateboard
has had a much greater reaction than the
action of the rider. This is not the case.
The reason the skateboard has traveled
farther is that it has less mass than the
rider—the Second Law of Motion.

94. If two
people, both on
skateboards, pus
h on one another
(action), they
move away in the
opposite
direction as the
push (reaction) .

95. When this man on
roller skates pushes
on the car, the car
doesn’t move
because it has great
mass but he who
has little mass rolls
backwards.

96. When a gun fires, the bullet moves
forward (action) causing the gun to recoil
(reaction).

97. When a balloon full of air is
sealed, the air pressure on
both inside and outside are
balanced, same pressure.
When the balloon is not tied
the air inside the balloon
escapes and then the air
pressure outside the balloon
is greater than inside.
As a result of the air moving out of the balloon
in one direction, the balloon moves in the
opposite direction—action, reaction.

98. In both the balloon and rocket engine shown
above, gases rush downward (action) causing
the balloon and rocket to go up (reaction).

99. Activity with balloon “rocket”

100. Along with Newton’s Laws of Motion, we now
consider Friction.
Considered by some to be one of the basic
forces, friction is the force that opposes motion
when an object’s surface is in contact with
other objects.
Although we seldom think about the role it
plays, friction is crucial to many things we
do....often making our lives more difficult
and often making it easier.

101. For example, it is friction between the
ground and the sole of our shoes that make
walking possible and it is lack of friction that
makes our feet slip on ice or highly polished
surfaces.
Without friction, the belts of machines would
slip, nails and screws wouldn’t hold, wheels
would spin without making things move.
At the same time friction wastes energy and
causes our machines to break down and to
wear out.

102. Friction is the force that opposes motion.
To move the blue bar over the orange bar, friction
could be a problem.
The greater the “load” the more “force” will be
needed to overcome “friction.”
force

103. The two major types of friction are:
Sliding friction: The rubbing together of the
surface of a moving body with the material
over which it slides.
Static friction: the force between two
bodies in contact that opposes sliding.

104. Sliding friction-can be easily demonstrated in
the classroom.
Put both of your hands together and move
them back and forth. Push your hands together
harder and move them faster. What do you
experience? Are your hands warming up? Do
you hear the sound of the hands moving
against each other?
Friction results from the surface of your hands
moving in opposite direction over each other.
Because your hands are in motion this type of
friction is known as sliding friction.

105. Many teachers have dealt with the
problem of moving the “big” box of new
books when all the carts were already
taken.
Here it
is in
graphic
form. Sliding friction

106. Sliding friction between the:
the broom and the floor
the foot and the floor
the hand and the hat

107. Now let’s look at static friction—the force
between two bodies in contact that tends to
oppose sliding.
In order to move something, you must first
overcome the force of static friction
between the object and the surface on
which it is resting.

108. Football players understand static friction well.
When they first hit this blocking sled, it very much
resists moving (static friction).
Once moving, the
sled becomes
somewhat easier
to push as sliding
friction becomes
the main force
resisting
movement.

109. If you have
every pushed a
car you have
experienced
static friction.
Initially you
have to push
really hard to
get the car
moving. That is
static friction.
Once you have the car rolling it is easier to keep the
vehicle moving. That is sliding friction.

110. This picture
shows static
friction, just
before the block
moves.
This picture shows
sliding
friction, while the
block is in motion.
It takes more force to get the block moving—static
fiction than it does to keep it moving—sliding fiction.

111. (Activity: Use scales to determine
the force (in newtons) required to
move a brick in basket.)

112. The amount of friction encountered, either
sliding or static, will depend on two things:
1. How smooth two surfaces are
that are touching.
2. The weight of the moving body
or the body you are trying to get to
move.

113. Even though a surface may look very
smooth, friction occurs in part because no
surface is perfectly smooth.
Rough surfaces have grooves and
ridges which catch on one another as
the two surfaces slide past each other.
When two surfaces try to move past each
other these little bumps collide and slow
down the motion of the surfaces.

114. The rougher a surface is, the more and bigger
bumps it has--more friction. The smoother a
surface is, the fewer and smaller bumps—less
friction.
For example if you slide a wooden block down
a ramp it will be slowed by friction. If you
sandpaper the block to make it smooth, the
block will be smoother and slide faster.
If you cover the block in sand paper (making it
rougher) the block moves even slower
because of the sandpaper’s rough surface.

115. Even surfaces that are apparently smooth can be
rough at the microscopic level. Under a
microscope, no surface is really "smooth."
No matter how
smooth the surfaces
may look to your
eyes, there are many
ridges and grooves.
The ridges of each surface can get stuck in the
grooves of the other.

116. Sandpaper
viewed
under a
microscope

117. Cloth
viewed
under a
microscope

118. Surface of a
tile viewed
under
a
microscope

119. Paper viewed under a microscope

120. Friction activity with different surfaces

121. Once more, the amount of friction
encountered, either sliding or static, will
depend on two things:
1. How smooth two surfaces are
that are touching.
2. The weight (or mass) of the
moving body or the body you are
trying to get to move.

122. The more mass or weight an object has the more
friction it has. Therefore it will take more force to
get it moving and more force to keep it moving.
A dump truck has more mass than a Smart Car.

123. The affect of weight on friction:
If it takes 10 newtons of force to slide a
block with a weight of 50 newtons, it will
take 20 newtons of force to slide a block that
weighs 100 newtons:

124. Very interesting!!!
Friction does not depend on the amount of surface
area in contact between an object and the ground, as
demonstrated in Example B.

125. So, is friction good or bad?
The answer, of course, is YES.
Sometimes friction works against us and
sometimes it works for us. It depends
on the situation.

126. How does friction works against us?
Friction between the moving parts of an
engine resists the engine’s motion and
turns energy into heat, reducing the the
efficiency of the machine and causing it to
wear out.
Friction also makes it difficult to slide a
heavy object, such as a refrigerator or
bookcase across the floor.

127. In others situations, friction is helpful.
We would be unable to walk if there was no
friction between our shoes and the ground. It is
that friction that allows us to push off the ground
without slipping.
On a slick surface, such
as ice, shoes slip and
slide instead of
gripping. This lack of
friction, makes walking
difficult.

128. Friction allows the tires on our vehicles to grip
and roll along the road without skidding.

129. Activity with person walking on board
on dowels.
Place a piece of plywood (could be about 3 x 3 ft.) over several aligned
wooden dowels and have a students try to walk on the plywood. The
board flies backward and the student stays put. (lack of friction)

130. Friction between nails, screws and beams
prevents the nails and screws from sliding out
stopping our buildings from collapsing.

131. We want tread
on our tires so
we can drive
our cars and to
prevent us from
slipping around
on wet surfaces.

132. We want tread our
footwear so we can
gain traction.

133. Often however, we wish to reduce friction.
Less friction makes it easier to move
things.
Reducing the amount of friction in a
machine increases the machine’s
efficiency. Less friction means less energy
lost to heat, less noise and less wear and
tear on the machine.

134. People normally use three methods to reduce friction.
The first method involves reducing the
roughness of the surfaces in contact.
For
example, sanding
materials lessens
the amount of
friction between
the two surfaces
when they slide
against one

135. The second method is to use smooth
materials which create less friction.

136. Or by
putting a
smooth
surface
under the
rougher
surface.

137. The third way to reduce friction is often the
best way--replace static or sliding friction with
rolling friction and/or add a lubricant.
Rolling friction: Instead of sliding surfaces
together, you can place rollers between
them.
Lubricant: By adding a thin layer of oil or
grease between two objects, you can
reduce static or sliding friction and lessen
wear on machines.

138. Rolling friction
When a cylindrical or spherical body rolls
over a surface, the force opposing the
motion is called rolling friction. Adding
rollers between two surfaces reduces
friction.

139. Ball bearings are
an example of
rolling friction.

140. Friction can be
reduced by adding
a lubricant such as
grease or oil
between the two
surfaces.
Lubricants reduce friction by minimizing
the contact between rough surfaces. The
lubricant’s particles slide easily against
each other resulting in far less friction.

141. Activity with shaving cream as a
lubricant and
Air Carts using air to separate surfaces
and reduce friction.

142. Lubricants decrease the amount of energy lost to
heat and damage to machine surfaces.

143. Oil Grease
Two common lubricants

144. That’s it for today...
MAY THE
FORCE BE
WITH YOU!