MOTIONMOTION

What is motion ? What are the different types of motion? What is the physics relating to motion called?

ok! we have answers to all these questions.

1. what is 1. what is motion?motion?

when a body is continuously changing its position with respect to the surroundings , then we say that the body is in motion.

EXAMPLE EXAMPLE

1.When an athlete is running on the ground then he is continuously changing his position with respect to the audience who are sitting at rest.

2.We are continuously changing our position since morning till night with respect to earth which is at rest.

3.The earth is continuously changing position with respect to sun which is at rest.

object in motion?object in motion?If you are standing in one place, and your

friend walks by you, are you moving relative to your friend?◦Is your friend moving relative to you?◦Is either of you moving relative to the

earth?

Answer:Answer:You are moving relative to your friend, and your friend is

moving relative to you!You (the Joker) are not moving relative to the earth, but

your friend is. You are both moving relative to the sun!Who is movingrelative to thecomputerscreen?

2.What are the different 2.What are the different types of motion?types of motion?

Linear motion : when a body moves either in a straight line or along a curved path, then we say that it is executing linear motion.

1. when a body moves in a straight line then the linear motion is called rectilinear motion.

eg ., an athlete running a 100 meter race along a straight track is said to be a linear motion or rectilinear motion.

2.when a body moves along a curved path then the linear motion is called curvilinear motion. eg., a planet revolving around its parent star

Other types of Other types of motion are :motion are :

Rotatory motion : A body is said to be in rotatory motion when it stays at one place and turns round and round about an axis. example :a rotating fan, a spinning top, the earth.

Oscillatory motion : a body is said to be in oscillatory motion when it swings to and fro about a mean position.

example : the pendulum of a clock, the swing etc.,

Vibratory motionVibratory motionWhen a certain part of a body always remains fixed and the rest of the body moves to-and-fro in a definite style, then its motion is called vibratory motion.

Periodic motionPeriodic motionA motion which repeats itself at regular interval of time is called periodic motion.

Multiple motionMultiple motionWhen an object possesses two or more types of motions at the same time, then such a motion is called multiple motion.

examples:When a spin bowler delivers a ball, the ball has a motion of spin(rotatory motion)while it moves toward the batsman(translatory motion).

SIMPLE PENDULUM AND SIMPLE PENDULUM AND RESTORING FORCERESTORING FORCE

PERIODIC MOTIONPERIODIC MOTION

The motion which repeats itself after fixed time intervals is called periodic motion

The best example of periodic motion are the pendulum clocks.

A SIMPLE PENDULUMA SIMPLE PENDULUM

A string with a mass at the end which is free to swing is called a pendulum.

TO AND FRO MOTIONTO AND FRO MOTION

The ball moves to and fro. It rises to extreme positions on both sides and reverses its motion

Oscillations gradually die down

LENGTH OF THE LENGTH OF THE PENDULUMPENDULUMThe length of the

string from the point of suspension to the mass is called the length of the pendulum.

It is denoted by L

MEAN POSITION OF THE PENDULUMMEAN POSITION OF THE PENDULUM

The central position of the pendulum (the starting position) is called the mean position of the pendulum.

It is labeled here as B.

EXTREME POSITIONS OF THE EXTREME POSITIONS OF THE PENDULUMPENDULUM

A and C are the extreme positions of the pendulum.

OSCILLATIONOSCILLATION

The motion of the mass from its extreme position A to C and back to A is called an oscillation.

TIME TAKEN FOR ONE OSCILLATIONTIME TAKEN FOR ONE OSCILLATION

The time taken for one oscillation is very short and therefore, difficult to measure accurately.

To find the time taken, we find the time taken for large number say 20 oscillations. This time divided by 20 will give us time taken for one oscillation.

PERIODIC TIME OF THE SIMPLE PERIODIC TIME OF THE SIMPLE PENDULUMPENDULUMThe time taken to complete one

oscillation is called the periodic time of the simple pendulum.

It is sometimes also called its period and is denoted by T.

RELATIONSHIP BETWEEN T AND LRELATIONSHIP BETWEEN T AND L

The equation is

gL

2T

The Period of the pendulum T is related to the length L by the relation

Factor affecting Time Factor affecting Time period of simple of period of simple of pendulum pendulum

Time period of simple pendulum depend on length and acceleration due to gravity (g)

Time period of simple pendulum does not depend on

mass of bob and material of bob

SCALARS AND VECTORSSCALARS AND VECTORSThe motion of objects can be described by words - words such as distance, displacement, speed, velocity, and acceleration. These mathematical quantities which are used to describe the motion of objects can be divided into two categories. The quantity is either a vector or a scalar. These two categories can be distinguished from one another by their distinct definitions:

Scalars are quantities which are fully described by a magnitude alone. Eg: distance , mass ,time ,volume etc

Vectors are quantities which are fully described by both a magnitude and a direction.

Eg :displacement , velocity , force ,acceleration etc.,

DISTANCE DISTANCE Distance is the actual path covered by a body, irrespective of its direction. Hence, it is scalar quantity.

DisplacementDisplacement Displacement is shortest distance travelled by a body from its initial position to its final position in particular direction Hence , it is a vector quantity. It indicates the change in position of a body. Therefore, has both length and direction

Here’s a problem (or Here’s a problem (or two)…..two)…..

If the earth spins on its axis at 1100 miles/hour, what is the speed of the Earth's rotation in feet per second?

The earth travels at 68,000 miles/hour as it moves around the sun. How many miles does the earth travel in one trip around the sun?

SpeedSpeedSpeed is the distance traveled in a given amount of timeSpeed=distance time The units for speed: meters/second (m/sec) kilometers/hour (km/hr)Speed that does not change is constant speed

SpeedSpeedSpeed = Distance

times = d t

Example: A car travels 450km in 5 hours. What is the speed of the car?

Answer:Answer:

Speed = distance time

Speed = 450 Km 5 hours

Speed = 90km hr

More practiceMore practice

1. How far can a plane travel if it flies 800km/hr for 9 hours?

2. How long does it take a ship to go 500 km if it travels at a speed of 50km/hr?

1. Answer1. Answer

Then: d = s t

800km 9hr = 7200km hr

2.Answer2.Answer

And then: since s = d t

t = d s500km 1hr = 10hrs 50km

VelocityVelocityvelocity is the rate of change of the position of an object, equivalent to a specification of its speed and direction of motion.Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving.If a car is said to travel at 60 km/h, its speed has been specified. However, if the car is said to move at 60 km/h to the north, its velocity has now been specified. To have a constant velocity, an object must have a constant speed in a constant direction.

VelocityVelocity

Speed in a given direction.

What is the velocity of a boat that travels from St. Peter to Mankato (10 miles) in 15 minutes?

AnswerAnswer

Speed = distance = 10miles

time 15minSpeed = 0.6666667 mil = 0.7 mil

min min

Change your answer to Change your answer to mi/hr!mi/hr!

0.67mi 60min = min hr

40 mi hr

Velocity can be Velocity can be classified as uniform classified as uniform and variable velocity and variable velocity

Uniform velocity :- If a body travels with a uniform speed in a constant direction, then the body is said to have uniform or constant velocity Variable velocity :- we normally come across variable velocities of moving bodies, Which means speed or direction or both speed and direction of moving bodies change constantly

SpeedSpeed velocityvelocity

It is the rate of change of distance

It is a scalar quantity

speed of moving body cannot be zero

It is the rate of change of displacement

It is a vector quantity

The velocity of a moving body become zero if it return to its initial position.

AccelerationAcceleration

The change in velocity is Acceleration

Acceleration is measured in m/sec2

Formula is:final velocity – original velocity time taken

Uniform and nonuniform Uniform and nonuniform accelerationacceleration

Acceleration can be uniform or nonuniform. Nonuniform acceleration requiresa change in acceleration. For example, when you’re driving, you encounterstop signs or stop lights often, and when you decelerate to a stop and thenaccelerate again, you take part in nonuniform acceleration.

Other accelerations are very uniform (in other words, unchanging), such asthe acceleration due to gravity on the surface of the earth. This accelerationis 9.8 meters per second2 downward, toward the center of the earth, and itdoesn’t change (if it did, plenty of people would be pretty startled).

ACCELERATIONACCELERATION

Problem: A car is moving in a straight line it speed up from 65km/hr to 74km/hr, in .17hrs What is the car’s acceleration.

Acceleration = Vf –Vi 1

t

74kmf – 65kmi 1 =

hr hr 0 .17hr

53 km/hr2

ACCELERATION!!!ACCELERATION!!!

Problem: Suppose a car moving in a straight line steadily increases its speed each second. First from 35 to 40 km/hr, then from 45 to 50 km/hr. What is its acceleration?

AnswerAnswer

15km 1h 1min 1 = .001 km hr 60 min 60 sec 3 sec2

DEACCELERATION

Deceleration ( “negative” acceleration):

A term commonly used to mean a decrease in speed.

Acceleration in a direction opposite to the direction of travel.

Deceleration is negative acceleration and has a negative value to indicate direction.

Relation between uniform Relation between uniform acceleration and time acceleration and time Suppose body start with initial velocity

of u m/s , Now body go on increasing its velocity by an amount a uniformly , let its final velocity be v m/s after a time of t sec

a = final velocity – original velocity time take

= (v-u)/t

Or v= u + at

This is called equation of motion