Subject :- Physics(Science)

Presented by:- Mayur Godbole

Class:- 9th

FRICTION – IS THE FORCE RESISTING THE RELATIVE

MOTION OF SOLID SURFACES, FLUID LAYERS, AND/OR

MATERIAL ELEMENTS SLIDING AGAINST EACH OTHER.

There are 5 types of

friction:Dry friction- it resists relative lateral motion of solid surfaces (in

contact). It is sub-divided into static and kinetic friction.

Fluid friction- it describes the friction between layers within a sticky

fluid that are moving relative to each other.

Skin friction- it is the force resisting the motion of a solid body

(through a fluid).

Lubricated friction- it’s a case of fluid friction where a fluid separates

two solid surfaces.

Internal friction- it’s a force resisting motion between the elements

making up a solid material while it undergoes.

Friction is one of the important part of nature. It is

necessary for us, the frictional force act as a “natural

stopper” if a ball thrown on the ground go in

any/specific direction it stops after sometime; it stops

because of frictional force acting on it. Friction can be

used in many ways :-Due to friction no energy is destroyed (it act as a energy

consumer).

It is mostly used in converting kinetic energy into heat

energy.

It is helpful for a person who is lost in a forest, it can be

used to

generate fire on a wood.

Due to friction only we can write on a paper.

Friction can produce sound.

FORCES ARE ALSO DESCRIBED AS A PUSH OR PULL ON AN

OBJECT. THEY CAN BE DUE TO PHENOMENA SUCH AS GRAVITY,

MAGNETISM, OR ANYTHING THAT MIGHT CAUSE A MASS TO

ACCELERATE. SI UNIT OF FORCE IS NEWTON AND THE SYMBOL = F.

Different types of forces are:Magnetic force

Frictional force

Gravitational force

Electrostatic force

Normal force

Magnetic force-It is the force that attracts iron towards itself. We can see

magnetic force in magnet kept near iron pins.

Frictional force-Frictional force is the force that opposes motion between two

surfaces.

Gravitational force-The force that acts on the objects and pulls the objects

towards earth (due to gravity).

Electrostatic force-It is the force which

Normal force-It is a force that acts on an object experiencing 0 net

force, since his weight is balanced by a normal force exerted by theground.

Can you guess the following

forces:Which force is acting on the

boy, after jump?

Which force is acting on the rat ?

If the person (who iscycling) stops paddlingthen, which force willact on the person andthe bicycle?

Newton SI

unitDyne Kilo-pound Pound force Poundal

1 N ≡ 1 kg · m/s² = 105 dyne ≈ 0.10197 kp ≈ 0.22481 lbF ≈ 7.2330 pdl

1 dyne = 10−5 N ≡ 1 g·cm/s² ≈ 1.0197×10−6 kp ≈ 2.2481×10−6 lbF ≈ 7.2330×10−5 pdl

1 kp = 9.80665 N = 980665 dyne ≡ gn·(1 kg) ≈ 2.2046 lbF ≈ 70.932 pdl

1 lbF ≈ 4.448222 N ≈ 444822 dyne ≈ 0.45359 kp ≡ gn·(1 lb) ≈ 32.174 pdl

1 pdl ≈ 0.138255 N ≈ 13825 dyne ≈ 0.014098 kp ≈ 0.031081 lbF ≡ 1 lb·ft/s²

How do we measure force?

We measure force by using an instrument

Know as force meter (Newton meter).

Force usually act in pairs.

Force acts in a particular direction.

We measure force in newtons.

We can’t always

see the force.

We sometimes feel the

effects they have on things.

The balloon in the

picture is affected

by forces.

Forces can make things

speed up.

When you hit a tennis

ball it speeds up.

Forces can make

things slow down or

stop.

A parachute can make an object

slow down because of air

resistance.

Forces can make things change

direction.

You can make a cricket ball

change direction by hitting it with

a bat.

Forces can make

things change shape.

If you squeeze or kick a football, it

will be compressed.

Forces can make things

turn.

You can use a

spanner to slacken

or tighten a nut.

Forces are every where

!