Motion

What is Motion ?

A body is said to be in motion (or moving) when it position changes continously with respect to a stationary object taken as refrence point. For eg: A moving car as shown below in the Image is in Motion.

Uniform motion

A Body has a uniform motion if it travel equal distance in equal interval of Time.

The Distance Time Graph for a body Having uniform Motion in a Straight line.

Non-uniform motion

A Body has a non-uniform motion if it Travels unequal distance in equal interval of time.

Difference between uniform & non-uniform motion

For eg:a car running at a constant speed of 10m p/s .it means car covering distance a distance 10m p/s.so, Its motion will be in uniform motion.

For eg:the motion of a free falling body is an example of non-uniform motion.

Uniform motionTravel equal distance in

equal interval of time.

The distance-time graph for a body having uniform motion is a straight line.

non-uniform motionTravel unequal distance

in equal interval of time.

The distance-time graph for a body having non-uniform motion is a curved line.

SpeedSpeed of a body is the distance travelled by it in per unit time.Tht speed of a body can be calculated by Dividing the ‘Distance Travelled’ by the ‘Time Taken’ to travel this Distance. So, the formula can be written as :

SPEED=Distance Travelled ______________ Time Taken

Average SpeedThe average speed of a body is the total distance travelled divided by the total time taken to cover the Distance.

For eg : A car which travels a distance of 100km in 4hours, the average speed is 100/4 =25km per hour. Although the average speed of car is 25 km per hour, it does not mean that car is moving at this speed all the time. When the road is Straight,or free the speed may be much more than 25km per hour. But on Bends (curved road), hills or in a crowded area, the speed may fall well bellow this average value.

Formula for Average Speed = TotalDistanceTravelled/Total Time Taken

DistanceThe Distance travelled by a body is the actual length of the path covered by a moving body irrespective of the direction in which the body travells.

Distance is a scalar quantity(Because it has magnitude only, it has no specified direction).

Distance can not be ZERO.But if the object or body travells from initial position to final position.Then we can say that Distance is ZERO.

Displacement When a body moves from one position to

another the Shortest (straight line)distance between the initial position & the final position of the body, along with direction, is Known as Displacement.

Displacement is a vector quantity(because it has magnitude as well as direction).

The distance travelled by a moving body cannot be zero but the final displacement of a moving body can be ZERO.

Difference between Distance & Displacement

Distance is a scalar quantity because it has the magnitude but not the specified direction.

Displacement is a vector quantity because it has the magnitude as well as the direction.

The Distance travelled by a body is the actual length of the path.

Distance is a Scalar quantity.

Distance can not be ZERO.

Displacement is the Shortest Distance between the initial position & the final position.

Displacement is a vector quantity.

Displacement can be ZERO.

Velocity & Acceleration Velocity of a body is the

distance travelled by it per unit time in a given direction.

Velocity=Distance travelled in a given direction /time Taken.

The si unit of velocity is the same as that of speed namely, metres per second(m/s or m s-1)

The direction of velocity is the same as the direction of displacement of the body.

Acceleration of a body is defined as the rate of change of its velocity with time.

Acceleration=change in velocity/time taken for change.

The change in velocity is the difference between the final velocity & the initial velocity.that is, change in velocity= final velocity-initial velocity

A=final velocity-initial velocity/time taken.

The si unit of acceleration is ‘’metre per second’’ or ‘’metre per second square’’.

Uniform velocityA body has a uniform velocity if it travels in a

specified direction in a straight line & moves over equal distance in equal interval of time,no matter how small these time interval may be.

The Velocity of a body can be changed in two ways :-

By changing the speed of the body.By keeping the speed constant but by changing the

direction.

uniform & non-uniform acceleration A body has a uniform accerelation if it travels in a straight line & its velocity increases by equal amount in equal interval of time.

Some example of uniformly accelerated motion :-

The motion of a freely falling body is an example of uniformly accelerated motion.

The motion of a bicycle going down the slope of a road when the rider is not pedalling & wind resistance is negligable, also an example of uniform accelerated motion.

A body has a non-uniform acceleration if its velocity increases by unequal amounts in equal intervals of time.

Example of non-uniformly accelerated motion :-

The speed (or velocity) of a car running on a crowded city road changes continously.at one moment the velocity of a car increases whereas at another moment it decreases. So, the movement of a car on a crowded city road is an example of non-uniform accerelation.

Retardation If the velocity of a body increases, the accerelation

is positive, & if the velocity of a body decreases, the accerelation is negative.

A body is said to be retarded if its velocity is decreasing.

Retardation is measured in the same way as acceleration, that is,retardation is equal to change in velocity

_____________________ & has the same units of time taken ‘’metres per second’’(m s -2) Retardation is actually acceleration with the

negative sign.

law of motion By sir.issac newton

newton’s law of motionNewton has given three laws to describe the

motion of bodies. These laws are known as Newton’s law of motion. The newton’s law of motion give a precise definition of force & established a relationship between the force applied on a body and the state of motion acquired by it.

newton’s first lawSome of the bodies(or object)around us are at rest,that is,they are stationary,whereas others are in motion.Newton’s first law describes the behaviour of such bodies which are in state of rest or of uniform motion in a straight line. According to Newton’s first law of motion : A body at rest will remain at rest,and a body in motion will continue in motion in a straight line with a uniform speed, unless it is compelled by an external force to change its states. Let us take an example to understand first law of motion more clear . Suppose we have a book which is lying on the table.It is at rest. The book will not move by itself that is,it cannot change its position of rest by itself.It can change its state of rest only when compelled by the force of our hands, that is, when we lift the book from the table. Thus, the position of rest of the book hass been changed by the external force of our hands. And this observation supports the first part of the first law of motion.The tendency of a body to remain at rest(stationary) or,if moving to continue moving in a straight line is called Interia. Newton’s first Law recognizes that every body has some Interia. INTERIA is that property of a body due to which it resists a change in its state of rest or of uniform motion..Greater the INTERIA of a body,greater will be the force required to bring a change in its state of rest or uniform motion.In fact mass is a measure of the interia of a body.If a body has more mass,it has more interia.That is, heavier object have more interia than lighter object.

Newton’s Second law oWhen two bodies,a heavy one and a light one,are acted upon by the same force for the same time,the light body attains a higher velocity(or higher speed) than the heavy one.But the momentum gained both the bodies is the same.The link between force & momentum is expressed in Newton’s second law of motion.oAccording to the Newton’s Second law of motion : The rate of change of momentum of a body is directly proportional to the applied force & takes place in the direction in which the force acts. The rate ofchange of momentum of a body can be obtained by dividing the ‘Change in momentum’ by ‘ Time taken’ for change. So, Newton’s second law of Motion can be expressed as :-

Force= Change in momentum/Time taken oConsider a body of mass m having an Initial velocity v. The initial momentum of this body will be mv. Suppose a force Facts on this body for time t & causes the final velocity to become v. The final momentum of this body will be mv. Now,the change in momentum of this body is mv-mu & the time taken for this change is t. So,according to Newton’s second law of motion : force=mv-mu/t or f=m(v-u)/toThus,the force acting on a body is directly proportional to the product of ‘mass’ of the body & ‘acceleration’ produced in the body by the action of the force,& it acts in the direction of acceleration. This is another definition of Newton’s Second Law of Motion. The relation F=m X a can be turned into an equation by putting in a constant K.oThus, Newton’s Second law of motion give us a relationship between ‘force’ & ‘acceleration’.oThe acceleration produced in a body is directly proportional to the force acting on it & inversely proportional to the mass of the body.

Newton’s third lawWhen one body influence another body by applying force,we say that the first body is interacting with the second body. In any interaction between two bodies,there are always two forces that come into play.And Newton’s third law of motion describes the relationship between the forces that come into play when two bodies interact with one another.According to Newton’s third Law of Motion : Whenever one body exerts a force on another body , the second body exerts an equal & opposite force on the first body.The force exerted by the first body on the second body is known as ‘Action’ & the force exerted by the second body on the first body is known as ‘Reaction’. Its Should be noted that’Action’& ‘Reaction’ are just forces.We can now write the another definition of of Newton’s third law of Motion : To every action there is an equal & opposite reaction.Action(Forcce) & Reaction(Force) act on Two different bodies , but they act Simultaneously.

Name- shubham rohilaclass- 9th croll no – 33