Chapter 10Chapter 1010.2 - Forces around us10.2 - Forces around us

GRAVITATIONAL FORCEGRAVITATIONAL FORCE

Gravitational force is a force ofGravitational force is a force of that that

the object the object ..

Gravitational force is a Gravitational force is a force. force.

attraction pullstowards earth

non-contact

Differences between Mass and WeightDifferences between Mass and Weight

Mass Weight

Definition

S.I. Unit

Instrument of measurement

An Object on Earth 1kg about 10 N

The same object on Moon 1kg about 1.67 N

Amount ofmatter inan object

Gravitational pull acting on an object

Kilogram NewtonSpring Balance

Beam Balance

Differences between Differences between Mass and WeightMass and Weight

From the table, we can From the table, we can conclude that:conclude that:Mass Mass , ,

and is always the and is always the ..Weight can Weight can , ,

depending on its location (due depending on its location (due to different gravitational field to different gravitational field strength, strength, gg..

does not changesamechange

To calculate WeightTo calculate Weight

W = mgW = mgwhere where W = weight (N)W = weight (N)

m = mass (kg)m = mass (kg)g = gravitational field g = gravitational field

strength strength (10 (10 N/kg)N/kg)

GravityGravity

Example 1Example 1

(a)(a) A object has a mass of 5 kg. A object has a mass of 5 kg. What is the What is the weight of the object weight of the object on earth given g = 10 N/kg?on earth given g = 10 N/kg?

GravityGravity

Example 1Example 1

(b)(b) If the gravitational field strength If the gravitational field strength on on Moon is 1/6 of Earth. What is Moon is 1/6 of Earth. What is the weight of the weight of the 5kg object on the 5kg object on Moon?Moon?

FRICTIONFRICTIONFriction is a force that Friction is a force that

..

..

Friction is a Friction is a force force (Friction exists when two objects (Friction exists when two objects are touching each other.)are touching each other.)

Friction produces Friction produces ..

opposes the

motion of an object

contact

heat

Friction can be USEFULFriction can be USEFUL

Friction helps us to Friction helps us to and and ..

(Friction prevented us from (Friction prevented us from slipping and falling)slipping and falling)

Friction helps us to Friction helps us to an an object.object.

stand walk

hold

Friction can be USEFULFriction can be USEFUL

Friction in brakes helps us to Friction in brakes helps us to .. or or vehicles. vehicles.

Friction is also used to produce Friction is also used to produce ..

stopslow down

fire

Friction can be a Friction can be a NUISANCENUISANCE

Friction causes Friction causes and and in objects.in objects.

Friction Friction moving moving object. object.

Friction produces Friction produces ..

Reduces efficiency

inmachinary.

wear tear

slow down

heat

Ways of Reducing Ways of Reducing FrictionFrictionUse of Use of as it as it

has less friction.has less friction.

Use of Use of . (eg. On . (eg. On the axles in bicycles, cars and the axles in bicycles, cars and machines)machines)

wheels & roller

ball bearings

Ways of Reducing Ways of Reducing FrictionFrictionUse of Use of to reduce to reduce

friction. (eg. Oil and grease)friction. (eg. Oil and grease)

Use of a Use of a . (eg. . (eg. Hovercrafts)Hovercrafts)

An object having a An object having a designed shape reduces friction designed shape reduces friction (eg. Boats, aircraft, fish)(eg. Boats, aircraft, fish)

lubricants

cushion of air

streamline

MAGNETIC FORCEMAGNETIC FORCE

Magnetic force is a Magnetic force is a force.force.

Magnets can exert a Magnets can exert a ..Like poles Like poles ..

(( each other apart) each other apart) Unlike poles Unlike poles ..

(( each other together) each other together)

non-contact

push or pullrepel

Pushattract

Pull

Uses of Magnetic Uses of Magnetic forcesforces

Maglev Trains (Magnetic Levitation)Maglev Trains (Magnetic Levitation)

Uses of Magnetic forcesUses of Magnetic forces ElectromagnetsElectromagnets

Electric Motors and GeneratorsElectric Motors and Generators