## MOTION

**INTRODUCTION**

In everyday life, we observed some objects are in rest and some are moving. For example, cars move, birds fly, deer running. In fact, stars, galaxy, solar system they all are moving. Or can say they all are in motion.

When a body changes its position with respect to time, then we called body is in motion.

For describing motion we must have a reference. Lets take an example of train, when you are in train, you can observe train is in rest and outside moving back, while if you are outside the train then you observed train moving.

**MOTION ALONG A STRAIGHT LINE**

The simplest type of motion is the moving in only one direction, can say motion in a straight line. It is also called linear motion

Types of linear motion

We can divide it into two types

a. Uniform linear motion: or can say constant velocity with 0 acceleration

b. Non-uniform linear motion: velocity have some acceleration.

**SPEED**

Distance, the total path travel by an object from its reference point. It is not depends on the direction. SI unit meter (m).

In a time interval, the total distance travel by the object is called call its speed. SI unit of speed is meter per second (m/s).

**π ππππ= (πππ π‘ππππ π‘πππ£πππππ)/(π‘πππ π‘ππππ)**

**π’=π π‘**Average Speed, total distance traveled by an object in total time ππ£πππππ π ππππ= (π‘ππ‘ππ πππ π‘ππππ)/(π‘ππ‘ππ π‘πππ)

**Velocity**

Displacement, minimum distance between final point and point of reference. It depends on direction. SI unit is meter (m).

Velocity, in a time interval, total displacement traveled by an object. It depends on direction. SI unit is meter per second (m/s).

**π£ππππππ‘π¦= (πππ πππππππππ‘ π‘πππ£πππππ)/(π‘πππ π‘ππππ)**

Average Velocity,

Since it depends on direction so it is the mean value of all velocities in total time.

**ππ£πππππ π£ππππππ‘π¦ = (ππππ‘πππ π£ππππππ‘π¦+πππππ π£ππππππ‘π¦)2 **

**π£ _{avg}=(π’+π£)/2**

**Acceleration**

Acceleration, rate of change of velocity. In other words, change in velocity in a time interval is called acceleration. It depend on direction of motion. SI unit is meter per second square (m/s^{2}).

**πππππππππ‘πππ= (πβππππ ππ π£ππππππ‘π¦) / (π‘πππ π‘ππππ)**

Also we can say acceleration can change the velocity in time t.

**π= (π£βπ’)/t**

Where **v** is final velocity**u** is initial velocity

and **t** is time taken**a** denotes the acceleration

**Example 8.1** An object travels 16 m in 4 s and then another 16 m in 2 s. What is the average speed of the object?

Solution: Total distance traveled by object = 16m + 16m = 32m

Total time taken= 4s +2s = 6s

And,

ππ£πππππ π ππππ= (π‘ππ‘ππ πππ π‘ππππ) / (π‘ππ‘ππ π‘πππ)

So,

ππ£πππππ π ππππ= 32π / 6π = 5.33ππ

**Questions**

**Distinguish between speed and velocity.**

**Answer**: Total distance traveled by an object in a time interval is called speed and total displacement traveled by an object in a time interval is called velocity. Speed not depends on direction, while velocity depends on direction.

**Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?**

**Answer**: When displacement is equal to distance covered by an object then average speed will be equal to the average velocity.

3. **What does the odometer of an automobile measure?**

**Answer**: It measures the distance traveled by wheel, or vehicle.

**What does the path of an object look like when it is in uniform motion?**

**Answer**: Straight line.

**Equation of motion**

(for graphical method download complete notes)

During the motion of object, we can calculate all the information about object like its velocity, acceleration, total distance, total time taken by the object, using equation of motion, and that is

(i) v = u + at

(ii) s = ut + Β½at^{2}

(iii) v^{2}β u^{2}= 2as

Where v is the final velocity, u is the initial velocity, a is acceleration, t is time taken and s is total distance covered by the object.

**Circular Motion**

Circular motion is the motion of an abject, which follows a circular path, or can say rotating on the circumference of a circle. In circular motion direction of velocity changes with the change in angle.

In daily life we can see many examples of circular motion, like fan, door, wheel etc.

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