## 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).

𝑠𝑝𝑒𝑒𝑑= (𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑)/(𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛)

𝑢=𝑠𝑡
Average Speed, total distance traveled by an object in total time 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑= (𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒)/(𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒)

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).

𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦= (𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑)/(𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛)

Average Velocity,

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

𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = (𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦+𝑓𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦)2

𝑣avg=(𝑢+𝑣)/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/s2).

𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛= (𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦) / (𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛)

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

𝑎= (𝑣−𝑢)/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,

𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑= (𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒) / (𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒)
So,

𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑= 32𝑚 / 6𝑠 = 5.33𝑚𝑠

Questions

1. 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.

1. 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.

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

Equation of motion

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 + ½at2
(iii) v2– u2= 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.

Categories: General