 # Speed of Moving Objects

## What are Moving Objects?

An object is said to be moving only when it changes its position.

Therefore, a moving object is characterized by its position, its direction of motion, and its direction of movement.

Let’s consider a block of mass, ‘m’ kept on the table.

Now, if we give it a push, it starts moving in the direction of force.

Newton's first law states that if an external force is applied to this block, it changes its position or sets into motion.

### Motion Can Be Found In Many Real-life Objects, Such As:

1. A ball thrown upward

2. A flying aeroplane

3. The falling of the dust particles on beating the floor mat.

4. Running animals

5. An electron moving in a direction perpendicular to the magnetic field.

### Examples Of Moving Objects

Motion can be of various types, some of them are discussed with examples below:

1. Rectilinear Motion - Motion of a body along the straight line.

1. Periodic Motion: The motion repeated after a fixed interval of time.

The revolution of planets around the sun in a fixed interval of time.

Such a motion is also called the simple harmonic motion.

1. Circular Motion:

A body follows a circular locus such that the force required to move a body uniformly in a circle acts along the radius and towards the center of the circle.

With continuous change in the direction of motion of the body, there is a change in velocity of the body and hence, it undergoes an apparent acceleration called the centripetal acceleration.

For example,  when a stone is tied to a string and on applying the force, the stone starts rotating about a fixed point.

### Speed Of Moving Objects

Basically, speed is the rate at which an object changes its position.

Speed of a body is defined as:

s  = Distance travelled/ time taken

The speed has a magnitude, and the direction of a body is unknown that’s why it is a scalar quantity.

A body having a mass, ‘m’  when pushed with a force, ‘F’ starts moving with a speed. In SI system, it is measured in meters per second  while in the cgs system, it is measured in cm/s.

Consider any vehicle, if its speed is constant, then we can calculate its constant speed.

It means the object is in uniform motion, and will cover equal distances in equal intervals of time. No matter how small the intervals maybe.

But if the body covers unequal distances in equal intervals of time and vice-versa, no matter how small the intervals may be.

However, such variations in speed can be calculated by an average speed.

The average speed =  Vₐᵥ  = Total distance travelled/Total time taken = 2 v₁v₂/(v₁+v₂) m/s

### Velocity of Moving Object

Let’s consider a path in which a body starts moving from a point to reach another point.

A body moves from A to reach B in time, ‘t.’

Here, distance between two points during time t is represented by a vector drawn from the initial to the final position.

Displacement takes into consideration the shortest distance to reach the destination.

So, velocity is calculated by,

V =  Displacement/ time taken (in m/s) = ΔX/Δ t = (X₂ - X₁)/(t₂ - t₁) m/s

A body in circular motion moves with a constant velocity, however the velocity vector keeps on changing with time.

A body moves 5 m/s north is a vector.

Then it moves 5 m/s west , with the same speed moves to the south and then to the west.

Here, the magnitude (speed) is the same while the direction is changing.

So, that’s why velocity is a vector quantity.

### Slow and Fast Motion

A body that is said to be moving slow or fast can be determined by the relative velocity of that object with respect to the other one.

It is defined as the rate at which the relative position of one object changes with respect to another.

Consider a train and a car, both moving in the same direction.

Driver of the car can see the train passing it.

It means that the train is in fast motion.

While for the passenger in the train, the car is at slow speed which means the car is in slow motion.

Here, the train and the car are moving with different velocities.

If the velocity of the train is v₁ and that of the car is v₂.

Then,  the relative velocity of train with respect to car’s velocity moving in the same direction is represented by:

v  =   (v₁ - v₂)

∴ v₁ > v₂ and value of v is positive.

We concluded that:

1. Slow motion means the movement of the car with respect to the train is relatively at slower speed.

2. Fast motion means the movement of the train with respect to the car is relatively at greater speed.

1. Write An Example of Slow and Fast Motion.

Let’s take a real-life situation, where you and your friend are going to a supermarket.

You prefer to travel on foot and your friend prefers to go by his car.

Both of you are traveling in the same direction, but your friend takes less time than you to cover the same distance.

So, here your friend is in fast motion while you’re in slow motion, because of his greater speed.

2. What are The Types of Speed?

There are four types of speed namely,

1. Uniform speed

2. Variable speed

3. Instantaneous speed

4. Average speed

3. Why is Motion So Important?

Earth’s rotation is the cause for the differences in daytime and night time as it rotates on its axis.

If it stops rotating, everything including rocks, topsoil, trees, buildings, your pet dog, and so on, would be swept away into the atmosphere.That’s why motion is important.

4. Can Sound Push You?

Sound waves exert pressure on us that effects are not usually noticeable.

But  if the intensity is cracked up high enough, then sound has an ability to counteract the effects of gravity.