# Motion Definition

You all use everyday objects that are in motion. For example, if you look about you and see the air moving, or if you have clocks with hands that move, you know that day and night are caused by the motion of the Earth around the Sun. So, we will carefully examine what exactly is meant by the term motion.

## Definition

Motion is defined as the change in the position of an object with respect to time and reference point. The six variables define motion, i.e., displacement, velocity, distance, acceleration, time, and speed. Motion includes things like a book sliding off a table, a person walking in a park, rattling windows, etc. There is motion in everything, including the air we breathe! The entire universe is in motion. Every physical process that takes place in the universe involves some motion. Motion might be quick or slow, but motion still remains present.

Example- If we compare a pole to a car, the pole will be stationary since the car can move, but the pole cannot. So, to determine whether a car is in motion or at rest, we must consider how it moves in relation to a pole or any other still object. You might also refer to this stationary item as a reference point.

## Rest and Motion

An object is considered to be at rest if it is stationary or not changing position in relation to its surroundings. On the other hand, an object is deemed to be in motion if it is moving and altering its position in relation to its surroundings.

For example- A person sitting on a stopped train might appear to be at rest in relation to the train, while an observer outside the train sees both the person & the train moving.

## Types of Motion

We may have seen that various items move in different ways. Some things travel on a curved path, whereas others move straight. Motion can be divided into three categories depending on its types, as follows:

• Linear Motion
• Rotary Motion/Circular Motion
• Oscillatory Motion

Linear Motion- An object moves in linear motion when it travels in a straight path at a constant speed/velocity. This is also known as rectilinear motion. An object goes in a straight line from one place to another when it is in linear motion, and it does not change its orientation or direction. It is a basic motion that may be seen in naturally occurring events and artificial objects.

Examples-

• A ball rolling down a straight ramp without any friction
• An object falling freely under gravity
• A car moving in a straight line on a frictionless surface

Rotary Motion- The motion of an item around a fixed point or axis is referred to as rotary motion, additionally known as circular motion. The thing moves in a circular route around the axis when rotating. The object's speed and direction constantly change as it revolves around the axis.

Example-

• The motion of the wheels on a car or bicycle
• The motion of a ceiling fan
• The motion of planets around the Sun.

Oscillatory Motion- When an object goes back and forth frequently around a central point, it is said to be in oscillatory motion. The object in oscillatory motion alternates between two places, known as the maximum displacement or the equilibrium position. The object's motion is periodic, which means it repeats itself at regular intervals, which is a common characteristic of oscillatory motion. The time it takes for an object to complete one full cycle of motion?from its maximum displacement back to its equilibrium position and then back again?is known as the oscillation period. The quantity of oscillation cycles that an object completes in a specified amount of time is known as its frequency.

Example-

• The motion of a pendulum
• The motion of a mass-spring system
• The motion of a vibrating guitar string.

## Scalar and Vector Physical Quantity

We study a variety of physical quantities such as distance, velocity, and many more. These numbers are generally categorized as either scalar or vector based on whether they provide full information about magnitude and direction or partial information, such as value or direction.

• Scalar Quantity- Scalar quantities are physical quantities with a simple magnitude or numerical value but do not have direction. Scalar quantities include things like mass, speed, temperature, energy, time, and distance.
Example- If you say that the car is moving at 60 km/h, you only give the magnitude of the speed, not its direction. Similarly, if you say that you weigh 60 kg, you only give the magnitude of your weight, not its direction.
• Vector Quantity- Vector quantities are physical quantities with both magnitude & direction. Displacement, acceleration, velocity, force, momentum, and other examples of vector quantities.
Example- If you say that the car is moving at a velocity of 50 km/hr to the west direction, you are indicating both the velocity and the direction of the motion. Similarly, if you say that a force of 40 N is operating on a block in the east, you give both the force's magnitude and direction.

## Distance and Displacement

Distance- It is a scalar quantity since it has just magnitude and no direction. For example, if you walk 10 km from point A to B, you have traveled 10 km. The distance is the same whether you travel from point A to point B or vice versa.

Characteristics of Distance

• It is the overall length of an object's path traveled, expressed in length units like meters or kilometers.
• Since distance is always a positive number, it can never be 0 or negative.
• By totaling the lengths covered along each section of the path, it is possible to determine the distance between two places.
• Distance is crucial for comprehending how objects move and is connected to ideas like time, velocity, and speed.
• It is a scalar quantity that may be added, multiplied, subtracted & divided using standard arithmetic operations.

Displacement- Because of its magnitude and direction, it is a vector quantity. The definition of displacement is the change in the position of an object with respect to a specific direction. For example, if you walk 10 kilometers from point A to point B in a north direction, that is the displacement.

Characteristics of Displacement

• Depending on the object's velocity, displacement may be positive, negative, or zero.
• It is the modification of the position of an object and is expressed in length units like meters or kilometers.
• An object's displacement is always either equal to or less than its travel distance.
• Displacement, intimately tied to other ideas like time, speed, and velocity, is crucial for comprehending how objects move.
• Since displacement is a vector quantity, vector algebra can be used to add, subtract, multiply, and divide it.
• Displacement is an essential concept in navigation since it is used to compute the direction and distance between two places.

## The Conclusion

Motion is the movement of an object from one point to another. When studying motion, we consider ideas like the speed at which an object is moving, the direction in which it is moving, and the rate at which its speed changes. We can explain and measure the motion of objects by comprehending these ideas, and we can implement this knowledge to address issues in many different domains. For instance, we can use our understanding of motion to create quicker and more effective vehicles or to examine how athletes move when competing.