© 2015 by brilliant classes - amazon s3 · 2016-09-14 · science : physics b) kinetic or sliding...

© 2015 by Brilliant Classes

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


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


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


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


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


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


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


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


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


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.


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?


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.


Name:___________________________ Date:____________________

Worksheet – 1

1. Circle the pictures that show gravity in red.2. Circle the pictures that show friction in blue.


Name:___________________________ Date:____________________

Worksheet –2

Draw an Illustration and describe examples of friction thatoccur around you.


Name:___________________________ Date:____________________

Worksheet – 3

Draw an Illustration and describe examples of friction thatoccur around you.


Name:___________________________ Date:____________________

Worksheet – 4

Complete the chart below.


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.


Name:___________________________ Date:____________________

Worksheet – 6

Write as many words or phrases about the Friction.


Friction

Name:___________________________ Date:____________________

Worksheet – 7


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?


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


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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© 2015 by brilliant classes - amazon s3 · 2016-09-14 · science : physics b) kinetic or sliding...

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