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Basics, Types, Use and Applications
Unit : FrictionScience : Physics
Friction : Basics, Types, Use and Applications
The following topics are included in this Unit:
Definition of FRICTION with example Basics of Friction Scientific meaning of Friction Principal of Friction Coefficient of Friction Causes of Friction Types of Friction with numerous examples: Dry friction
1. Static friction2. Sliding friction
Fluid friction Rolling friction Determination of Friction Methods to reduce Friction Usefulness of Friction Fun-facts about the Friction Effect of Friction on moving objects Student worksheets/Friction Lab exp. for the assessment
and review of their knowledge
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Science : Physics
Basics of Friction
• Suppose you decide to ride a skateboard.• You push off the ground and start moving.• According to Newton’s First Law of Motion, if no other
forces are acting on your skateboard, you will continue tomove….BUT……….
What happens?• Your skateboard slows down because of friction. The amount of friction depends on two things:1. Kind of surface.2. Forces pressing the surfaces together.
Unit : Friction
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Science : Physics
Scientific meaning of ‘Friction’ :
• Friction is a force. A frictional force arises when two
substances contact each other.
• Friction is the resistance of motion when one object rubs
against another.
• Friction works against the motion and acts in the opposite
direction.
• For example when you try to push a toy car along the floor.
Unit : Friction
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Science : Physics
Principles of Friction :
• Friction acts parallel to the surface that are in contact.
• The direction that friction acts is OPPOSITE the direction ofthe motion (or intended motion).
Fweight
Fnormal
FappliedFfriction(k)
Co-efficient of Friction :
• Frictional Force, both static and kinetic, is directlyproportional to the force pressing the two surfacestogether. The more weight, the more friction.
normal
(kinetic)friction
kinetic
normal
(static)friction
static
normalfriction
F
F
F
F
FF
normalfriction FF
(μ = Co-efficient of friction)
Unit : Friction
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Science : Physics
Causes of Friction :
• Even though a surface may look smooth, if you magnify the
surface it isn’t smooth.
• Everything is made of molecules. The molecules come
together to make bumps. Some surfaces have molecules
that leave large bumps and some leave smaller bumps, but
all surfaces have bumps.
• Microwelds occur when two bumpy surfaces are rubbed up
against each other they stick together.
• The greater the force on the object, the greater the force
of the microwelds and the greater force is needed to
overcome the microwelds to move the object.
• When one object is sliding on another it starts to
slow down due to the friction. This means it
loses energy.
• The energy doesn't disappear it changes from
moving energy (also called as kinetic energy) to
heat energy.
• This is why we generally use to rub our hands
together when its cold. By rubbing them we
generate friction and, therefore, the heat.
Unit : Friction
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Science : Physics
b) Kinetic or Sliding Friction : It slows down an object that
slides.
1. Dry Friction : Dry friction occurs when two solid objectstouch each other. There are two types under dry friction.
a) Static Friction : It prevents an object from moving when
force is applied means static friction tries to keep an
object at rest.
Ex : Walking - For each step you take pushes against the
Earth.
Without the friction, you would slip and fall with each
step.
Types of Friction :
No
Static Friction
No Motion
Pushing Force
Friction
Sliding Friction
Motion
Pushing Force
Friction
Unit : Friction
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Science : Physics
2. Fluid Friction :
• Fluid friction involves a fluid or air. The air resistance on an
airplane or water resistance on a boat is fluid friction.
• Air pushes against you
• It acts on the forward moving part of the object
• Ex : 1. Front of the car
2. When you ride bicycle, the air pushes your hairand the clothes back.
3. Rolling Friction :
• Rolling friction occurs when a round surface rolls over a
surface, like a ball or wheel.
Ex : If you push a box across the room, there is sliding
friction between the bottom of the box and the floor.
Ex : Rubbing Hands etc.
Fluid Friction
Unit : Friction
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Science : Physics
• It allows the wheels to turn by pushing back so tire moves
forward.
Ex : Bicycle or car etc.
Ex : When you ride your bike through water there may not
be enough friction between the tire and the ground to
move forward and so the bike skids.
Unit : Friction
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Science : Physics
a) Ff_max = FN
b) Ff_max is the maximum force of friction
c) (Mu) is the coefficient of friction
d) FN is the normal force
e) Friction can range in value from -Ff_max to +Ff_max
f) depends on the types of surfaces that are interacting. It
would be low for rubber on ice, but high for rubber on
asphalt. It also depends on whether the surfaces are
moving relative to each other ( static or dynamic ).
g) Measures of friction are based on the type of materials
that are in contact. Concrete on concrete has a very high
coefficient of friction. That coefficient is a measure of
how easily one object moves in relationship to another.
h) When you have a high coefficient of friction, you have a
lot of friction between the materials. Concrete on
concrete has a very high coefficient and Teflon on most
things has a very low coefficient.
i) Teflon is used on surfaces where we don't want things to
stick; such as pots and pans.
Determination of Friction :
Unit : Friction
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Science : Physics
• A good example of this is a ball or wheel. They roll to help
reduce friction.
• Lubricant like grease or oil. Ex. : Machines and engines use
grease and oil to reduce friction and wear so they can last
longer.
• To change the types of materials in contact with one another.
Ex, ice contacting with steel would produce less friction than
rubber would on concrete. This is why ice skates slide so
easily on the ice, but you don't slip when wearing rubber
shoes on the sidewalk. These different materials are said to
have different "coefficients of friction".
Unit : Friction
Methods to reduce the Friction :
• Sometimes we want to reduce friction. For example,
moving parts inside a car engine are lubricated with oil, to
reduce friction between them.
• The oil holds the surfaces apart, and can flow between
them.
• The reduced friction means there is less wear on the metal
and less heat produced.
• In some cases we want to prevent friction so it's easier to
move.
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Science : Physics
Fun facts about Friction :
• Although wheels are great for rolling and reducing friction,
they couldn't work without friction.
• It would be really tough just to stand up without friction.
• Friction can generate static electricity.
• The harder two surfaces are pressed together, the more
force it takes to overcome the friction and get them to slide.
Unit : Friction
Use of Friction :
• Friction is also a great boon to us. After all, we would all just
be sliding around everywhere if there wasn't friction to
keep us steady.
• Friction is also used in car brakes, when we walk or climb a
hill, in sandpaper, making a fire and more.
• Ice causes very little friction, which is why it is easy to slip
over on an icy day. But this is a good thing for ice skating
and sledging.
• All kinds of friction cause moving objects to slow down or
stop.
• The frictional force is found by multiplying the objects
weight by a coefficient of friction.
Effect of Friction on a moving object?
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Science : Physics Unit : Friction
• The value of co-efficient of friction is usually less than one,
but can be higher than one (for example with rubber tyres
on dry tarmac). Therefore friction requires a greater force
to be applied to move the object.
• Friction is a force that acts against a moving object to slow
it down. A type of friction is air resistance.
Friction opposes the direction in which the object is
moving, causing the object to decrease in speed or stop all
together.
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Name:___________________________ Date:____________________
Worksheet – 1
1. Circle the pictures that show gravity in red.2. Circle the pictures that show friction in blue.
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Name:___________________________ Date:____________________
Worksheet –2
Draw an Illustration and describe examples of friction thatoccur around you.
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Name:___________________________ Date:____________________
Worksheet – 3
Draw an Illustration and describe examples of friction thatoccur around you.
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Name:___________________________ Date:____________________
Worksheet – 4
Complete the chart below.
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Type of friction Definition & Example
Dry friction
Static friction
Sliding friction
Fluid friction
Rolling friction
Name:___________________________ Date:____________________
Worksheet – 5
Draw an arrow to show where friction is occurring ineach picture.
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Name:___________________________ Date:____________________
Worksheet – 6
Write as many words or phrases about the Friction.
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Friction
Name:___________________________ Date:____________________
Worksheet – 7
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Prepare Friction K W L chart
What do youknow aboutthe Friction ?
What do youwant to knowabout theFriction ?
What did youlearn aboutthe Friction?
Name:___________________________ Date:____________________
Friction Lab Exp. – 8
Which type of material will create the least amount offriction for a car when it is going down a ramp?
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Type of material How far the car went (Cm)
Carpet / Tile
Sand paper
Wax paper
Bubble wrap
•Conclusion:
•________________________________ had the least amount of the friction.
Imp : Directions for this Lab is given on the last page.
Name:___________________________ Date:____________________
Friction Lab Exp. – 8
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Imp : Directions for the friction Lab :
During this lab divide your students into groups (Three or four). Giverequired materials to each group:
The students will be making the car go down the ramp to see howfriction affects how far the car will go. Here are the steps:
1.Have the students place the binder on floor. If you have carpet ortile, tick proper surface type and record the readings.
2. Explain to the students they will be making the car go down the“ramp” (binder) and measuring how far the car goes. Tell studentsto measure from the edge of the binder to the end of the car tokeep it consistent. DO NOT PUSH THE CAR! Let gravity do the work.
3. The students will release the car from the top of the binder andthen measure how far it goes. They will then record themeasurement.
4. The sandpaper is next. I use about one foot. The students feel thepaper to see how rough it is. Then, have them open the binder andplace a bit of the sandpaper in the binder. Most of the paper will besticking out. This is to create a smooth transition from the binder tothe sandpaper. Have the car go down the ramp and measure.
5. Repeat with the wax paper and the bubble wrap.6. Now create a chart with all the groups’ results together and talk
about making sure an experiment is reliable.7. Make the conclusion for all the cases.
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