Newtons three laws of motion around us

Newton's laws of motion are three physical laws that

together laid the foundation for classical mechanics. They describe the relationship

between a body and the forces acting upon it, and its motion in

response to said forces. They have been expressed in several different ways over nearly three

centuries, and can be summarised as follows:

First law: When viewed in an inertial reference frame, an

object either remains at rest or continues to move at a constant velocity, unless acted upon by

an external force.

Secod law: F = ma. The vector sum of the forces F on an object

is equal to the mass m of that object multiplied by the

acceleration vector a of the object.

Third law: When one body exerts a force on a second body, the second body simultaneously

exerts a force equal in magnitude and opposite in direction on the first body.

The three laws of motion were first compiled by Isaac Newton

in his Philosophiæ Naturalis Principia Mathematica

(Mathematical Principles of Natural Philosophy), first

published in 1687.Newton used them to explain and investigate

the motion of many physical objects and systems. For

example, in the third volume of the text, Newton showed that

these laws of motion, combined with his law of universal

gravitation, explained Kepler's laws of planetary motion.

The initial stage in the development of classical mechanics is often referred to as Newtonian

mechanics, and is associated with the physical concepts employed by and the mathematical

methods invented by Newton himself, in parallel with Leibniz, and others. This is further

described in the following sections. Later, more abstract and general methods were

developed, leading to reformulations of classical mechanics known as Lagrangian mechanics

and Hamiltonian mechanics. These advances were largely made in the 18th and 19th

centuries, and they extend substantially beyond Newton's work, particularly through their use

of analytical mechanics. Ultimately, the mathematics developed for these were central to the

creation of quantum mechanics.

Sir Isaac Newton[ 25 December 1642 – 20 March 1727] was an English physicist and mathematician (described in his own day as a "natural philosopher") who is widely recognised as one of the most influential scientists of all time and as a key figure in the scientific revolution. His book Philosophiæ Naturalis Principia Mathematica ("Mathematical Principles of Natural Philosophy"), first published in 1687, laid the foundations for classical mechanics. Newton also made seminal contributions to optics and shares credit with Gottfried Leibniz for the invention of calculus.

WHY ARE NEWTONS LAWS OF MOTION IMPORTANT

Newton first published his three laws of motion in 1687,& physics

students have been learning them in class ever since.They are

important to us because:

They work around

They represent mankinds first great success at describing diverse

aspects of nature with simple mathemitacal formulas.

They form the most intuitively appealing physical theory.

They lay the groundwork for later physics development

NEWTONS LAW'S WORK

Nature has been superseded by special relativity, quantum mechanics, & field

theory.Newton's law's fail miserably inside molecules & in distant outer space , in

fact they fail to even exolain some important features of classical

electromagnetism.However , there's a catch ; all these other theories reduce to

Newton's laws the realm of everyday's life.For a wide variety of situations,

Newton's law work just fine.This is why physicists didn't discover any problems

with them for over two hundred years. Newton's laws can predict the motion &

interactions of objects well enough to:

Build & navigate spaceships

Simulate car crashes

Measure the mass of the earth & other solar system bodies

Explain how airplains generate lift

Improve your athletic abilities

Nearly everything we experience in dialy life that involves motion can be explained

by Newton's laws in very accurate ways,& nearly you use in dialy life was designed

with Newton's laws in mind

NEWTON'S LAWS ARE A TRIUMPH FOR HUMANITY

Newton's laws were not the first mathematical description of the universe.People

have actually been using math to predict the movement of the planets since

claudius ptolemaeus developed his model in the second century AD.This system

was eventually replaced with the Copernican system & even later by Kepler's laws

However, these systems all had numerous 7 arbitary set of rules.they worked,but

made very little sense.Newton's laws of motion (along with his law of universal

gravitation,which gave the appropriate form of the force to use in the second law)

were able to explain planetary motion with fewer concepts,those same three laws

applied to things on earth as well.

Newton also showed that the same laws govern celestial motion & terrestrial

motion.For all of history until that point,people hadbelieved that the heavens were

so sacred that they constituted the totally different realm.Newton proved

otherwise! Newton showed that the human brain was capable of understanding

deep properties of the natural world.This accomplishment was totally

unpresedented & it greatly influnced scientific & religious communities

NEWTON'S FIRST LAW OF MOTION

http://www.youtube.com/watch?v=OHw80HXSuAQ

In detail about 1st law

“ everybody presists in its state of being at rest or of moving straight forwars,

except insofar as it is compelled to change its state by force impressed” is the

defination of Newton's first law of motion.

The ancient greek philosopher Aristotle had the view that all objects have a

natural place in the universe;that heavy objects wanted to be at rest on the earth

& that light objects like smoke wanted to be at rest in the sky & the stars wanted

to remain in the heavens . He thought that a body was in its natural state when it

was at rest ,& for the body to move in a straight line at a constant speed an

external agent was needed to continually propel it,otherwise it would stop

moving. Galileo Galilei ,however ,realised that a force is necessary to change the

velocity of a body , that is accleration, but no force is needed to maintain its

velocity.in other words,Galileo stated that,in absence of a force,a moving object

will continue moving. The tendency of objects to resist changes in motion was

what Galileo called it INERTIA. This sight was refined by Newton, who made it

into his 1st

law ,also known as the “LAW OF INERTIA”-NO FORCE MEANS NO

ACCLERATION, & hence the body will maintain its velocity. As Newton's 1st

law is

a restatement of the law of inertia wich Galileo had already described, Newton

appropriately gave credit to Galileo.

Animated view of 1st law

Examples for inertia of motion

● A pearson riding a bicycle along a levelled road does not

come to rest immediately after he stops pedelling.Thus the

cycle continous to move due to inertia of motion .Finally it

comes to rest , after travelling some distance, because of

the friction exerted by the ground.

INERTIA & MASS

● To change the velocity of a body , one has

to apply force. Consider 2 bodies of

unequal masses initially at rest. If you push

the bodies equally hard for equal time

,both'll start moving .But the lighter one

starts with larger velocity & the heavier

one starts with smaller velocity. Thus the

heavier one has resisted the change of

more effectively than the lighter one.

Hence heavier bodies have larger inertia

than lighter ones. So ,MASS IS A

QUANTATIVE MEASURE OF INERTIA .

NEWTONS SECOND LAW OF MOTION

“ THE CHANGE OF MOMENTUM OF A BODY IS A PROPORTIONAL TO THE MOTIVE

FORCE IMPRESSED ON THE BODY, & HAPPENS ALONG THE STRAIGHT LINE ON

WHICH THAT IMPULSE IS IMPRESSED.” is the defination of Newton's 2nd

law of

motion.

Motte's 1729 translation of Newtons Latin continued with newtons commentary on

the second law of motion , reading ;

“ IF A FORCE GENERATES A MOTION , A DOUBLE FORCE WILL GENERATE DOUBLE

THE MOTION, A TRIPLE FORCE TRIPLE THE MOTION, WEATHER THAT FORCE BE

IMPRESSED ALTOGETHER AT ONCE, OR GRADUALLY AND SUCCESSIVELY .AND

THIS MOTION (BEING ALWAYS DIRECTED THE SAME WAY WITH THE GENERATING

FORCE), IF THE BODY MOVED BEFORE IS ADDED TO OR SUBTRACTED FROM THE

FORMAL MOTION, ACCORDING AS THEY DIRECTLY CONSPIRE WITH OR ARE

DIRECTLY CONTARY TO EACH OTHER; OR OBLIQUELY JOINED , WHEN ARE

OBLIQUE, SO AS TO PRODUCE A NEW MOTION COMPOUNDED FROM

DETERMINATION OF BOTH

● SI unit of force is NEWTON & is denoted by N.

● IN c.g.s system the unit of force is called DYNE.

● Newton & dyne are called absolute values of force.

● Gravitational force on an object of unit mass is known as gravitational unit of force.

● In MKS system, the gravitational unit of force is the KILO GRAM FORCE(kgf).In C.G.S

system ,the gravitational unit of force is the GRAM FORCE(gf).

ABSOLUTE &

GRAVITATIONAL

UNITS OF FORCE

LINEAR MOMENTUM

● The product of mass of a body & its velocity is called LINEAR

MOMENTUM or simply momentum of the body.If M is the mass of the

body ,V is the velocity , the momentum of the body is given by ;

● p=mv

● Linear momentum is a vector in the direction of velocity. Newton's

second law can be written in terms of momentum mv-mu divided by t

● Thus ,the alternate way of stating Newton's 2nd law is :

● The resultant force on a body is equal to the change in its linear

momentun per unit time.

TO DERIVE AN

EXPRESSION FOR FORCE

A force 'F' acts on a body of mass 'm' for a time 't' & changes its velocity

from 'u' to 'v.

The initial momentum of the body =mu

The final momentum of the body =mv

The change in momentum of the body in time 't' =mv-mu=m(v-u)

From Newton's 2nd law,

force=change in momentum by time = m(v-u), divided by t

IMPULSE OF A FORCE

When a tennis ball is hit by a player,or when a football, at rest , is

kicked towards a goal post, a large change in momentum is observed

in a very short interval. The force exerted by the floor or by the leg ,

acts only during a short period of contact with the ball. In such

cases, a very large magnitude force acts for a small interval of time.

Such forces are called IMPULSE FORCE.

Measurement of the magnitude of impulse force & time during which

it acts is very difficult. But the product of force & time can be

determined by measuring change in momentum of the body.

Ft=mv-mu

The quantity Ft is called IMPULSE OF FORCE. THE IMPULSE OF A

FORCE .The impulse of a force applied on a body is equal to the

change in the linear momentum of the body produced by the force.

NEWTON'S THIRD LSW OF MOTION

“TO EVERY ACTION THERE IS ALWAYS OPPOSED AN EQUAL ACTION : OR THE

MUTUAL ACTIONS OF TWO BODIES UPON EACH OTHER ARE ALWAYS EQUAL, &

DIRECED TO CONTRARY PARTS “ is the defination of Newton's 3rd

law of motion.

Newton used the 3rd

law to derive the law of conservation of momentum; from a

deeper perspective ,however , conservation of momentum is the more fundamental

idea ,& holds in cases where Newton's 3rd

law appears to fail, for the first time a

unified quantitative explanation for a wide range of physical phenomena.

In quantum mechanics concepts such as force , momentum ,& position are defined

by linear operators that operate on the quantum state; at speeds that are much lower

than the speed of light, Newton's laws are just as exact for these operators as they

are for classical objects. At speeds comparable to the speed of light , the 2nd

law

holds in the original form F=dp/dt

CONTD..........

Click to A pair of forces exerted by two bodies on one another is

called an action reaction pair. The alternate statement of 3rd law is :

TO EVERY ACTION, THERE IS AN EQUAL & OPPOSITE REACTION

An example is that of a baloon-

A baloon forces the air in the downeard direction wgereas reaction to

this moves the baloon in upward direction.

CONSERVATION OF LINEAR MOMENTUM

According to Newton's 1st

law, a particle remains at rest or moves with a constant

velocity if the total force acting on it is zero. In this case, linear momentum ,which is

mass times the velocity ,also remains a constant. Thus, linear momentum remains

constant in the absence of external force. This is true in case of system of particles

as well. We define linear momentum of a system as the vector sum of the moments of

all the particles of the system. Then the law of conservation of linear momentum can

be stated as followed

If the net xternal force is on a system is zero , the linear momentum of the system

remains constant

If the momentum of some particle is increased ,then the momentum of some other

particle must decrease to keep the net momentum of the object a constant

EXAMPLE OF ROCKET

PROPULSION

The principle of rocket propulsion is based on the 3rd

law of motion.

Rockets eject gases at high pressure through thrir lower ends. The

escaping gases exert reactional force on the rocket therby

acclerating the rocket . After complete burning of the fuel, the

compartment is detached from the rocket. Thus the rocket becomes

lighter 7 will have a greater accleration

DONE BY-

HARSHITH.K9th' A' ROLL NO-22