Motion

We see motion all around us every day. Some things move fast, like a cricket ball. Some things move slowly, like a person walking. Some motion is smooth, some is jerky.

By observing motion carefully, we can describe how an object moves: where it starts, where it goes, and how long it takes to reach there.

We always compare the position of an object with some fixed point. This fixed point is called a reference point or origin.

For example, when you say, “The car is 20 meters away from the shop”, the shop is your reference point.

We can think of motion as the position of an object changing with time. We can write it in a simple way as:

\( \text{Position at time } t = x(t) \)

This simply means that position depends on time.

An object is said to be at rest if it does not change its position with time with respect to a chosen reference point.

For example, a book lying on a table is at rest with respect to the table.

An object is said to be in motion if it changes its position with time with respect to a chosen reference point.

For example, a car moving on the road is in motion with respect to a tree on the roadside.

Sometimes, whether an object is at rest or in motion depends on who is observing it. For a passenger inside a moving bus, another passenger appears to be at rest. But for a person standing on the road, both passengers are in motion.

If an object moves along a straight line, we say it has rectilinear motion. Example: A train moving on a straight track.

If an object moves along a curved path, we say it has curvilinear motion. If the path is a circle, it is circular motion. Example: The hands of a clock or the blades of a fan.

Sometimes, an object moves back and forth about a point. This is called oscillatory or periodic motion. Example: A swinging pendulum or a child on a swing.

To say whether motion is fast or slow, we compare the distance covered in a given time. If an object covers more distance in less time, it is faster.

Later, we use ideas like speed and velocity to describe this more exactly, but the basic idea is simple: fast motion means changing position quickly; slow motion means changing position slowly.

When you say, “It takes me 10 minutes to walk to school”, you are linking motion with time.

• The starting point is your home.
• The ending point is your school.
• The time taken is 10 minutes.

This is a simple way of describing motion in daily life.

• Water flowing from a tap.
• A ceiling fan rotating.
• A refrigerator door opening and closing.

All these are examples of objects changing their position with time.

• Cars, buses, and cycles on the road.
• Leaves moving in the wind.
• People walking or running in a park.

Each of these motions can be understood as an object changing its position with time.