Lesson 1Week2

8/13/2019 Lesson 1Week2

1/6

Lesson 3: Newtons Laws I and II

Contents:

Law of Inertia

Forces and Work done

Energy and Power

Introduction

All the objects resist a change in velocity. An object at rest needs some force to make itmove and if it is moving it takes some force to make it go faster, slower or changes its

direction.

Inertia and Mass

Inertia is resistance to change in velocity. Inertia is also resistance to change inacceleration. Since acceleration is the change in velocity.

Larger masses have larger inertia and smaller masses have smaller inertia. Therefore

Mass is also the measure of inertia

Force

Forcesare pushes, pulls, or twists.

Forces are measured in Newton!"#

Forces have directions.

Forces act in pairs. If you $ush on something, it will $ush on you.

Different Types of Forces

Drag Forces

Dragsometimes called air resistanceor fluid resistance" refers to forces that o$$ose

the relative motion of an object through afluida liquidorgas". %rag forces act in adirection o$$osite to the oncomingflow velocity.


2/6

Drag force

Air esistance

Air resistance is a ty$e of force that $ushes against moving objects. &ecause airresistance slows things down it is also a ty$e of friction. Things that need high velocity

are today streamlined to reduce resistance or drag. For e'am$le racing cars, submarines

and aero$lanes and rockets are streamlined.

Ter!inal "elocity

A free falling object achieves its terminal velocity when the downward force of gravity

Fg"e(uals the u$ward force of drag Fd". This causes the net force on the object to be)ero, resulting in an acceleration of )ero. ...

*.g. Forces acting on a $arachutist.


3/6

Friction

Frictionis the force between to surfaces rubbing together. It is high if the surfaces are dry

and rough and it is low if the surfaces are smooth and wet.

Ad#antages and Disad#antages of Friction

Friction $lays a vital role in our daily life. It hel$s us to walk on the ground withoutsli$$ing and also the tyres of the cars gri$ on the ground. It is used in most braking

systems. The main disadvantage of friction is that it $roduces heat and damages various

$arts of machines. It creates noises and slowdown the machines causing loss of money.

To reduce friction, the $arts of machines which are moving over one another must be$ro$erly lubricated by using oils, grease and lubricants of suitable viscosity.

$alanced and %n&alanced Forces

If the $air of forces acting on an object at rest is balanced and resultant is )ero, the object

will remain stationary. If the forces become unbalanced the object accelerates along thedirection of the resultant.


4/6

If the $airs" of forces acting on a moving object is balanced and resultant is )ero, the

object continues in constant velocity. If the forces are unbalanced, the object accelerates,decelerates or changes its direction according to the resultant force.

Newtons First Law of Motion 'Law of Inertia(

An obect will continue in a state of rest or motion in a straight line unless an e!ternal

force acts u"on it#

+ork done and *nergy

+hen a force makes something move, work is done. *nergy is needed to get work done.

+hen work done, energy is transferred from one form to another.

)or* done + force , distance !o#ed in the direction of the force 'displace!ent(

W = F's

nit of work done is - or N!


5/6

E!am"le$The following diagram shows a block of wood been $ulled by a hanging weight of -!.

ow much work does the block of do to move the distance of /m.

+ 0 F ' s

0 -! ' /m 0 / !m or / 1

.nergy

Things have energy if they are able to do work. The following things have energya" uman body

b" A tank of $etrol

c" A stretched s$ring

d" An object ke$t on the table with is some distance above the ground

Energy is ca"acity to do work# The unit of energy is -oules '-(.

Different for! of energy

Potential Energy2 3bjects have $otential energy if they have been moved into a $osition

which they can do work when released.%inetic Energy2 4oving objects have kinetic energy

&hermal Energy2 eat energy radiates by hot objects. This energy relates to the

movement of molecules or atoms of the material.Electrical Energy2 *nergy delivered by the generators and batteries.

'hemical Energy2 Food and fuels have chemical energy

Wave energy2 *nergy of the sound waves and electromagnetic waves or water waves etc.


6/6

Law of Conser#ation of .nergy

Energy cannot be created or destroyed( but it can be changed from one form into

another#

/inetic .nergy

5.* 0 6 mv/

E!am"le

7alculate the 5.* of a car of mass -888 kg travelling at a velocity of 9 m:s.

5.* 0 6 mv/0 8.; ' -888 ' 9 ' 9 0

Lesson 1Week2

Documents

Transcript of Lesson 1Week2