What is Motion?

Motion is the change in position over time, and it’s always measured with reference to a specific point, called the origin. To describe this change, we use two key terms: distance and displacement. Distance is the total path covered during motion and only has magnitude, while displacement is the shortest distance between the starting and ending points, requiring both magnitude and direction. Here, we'll explore the concepts of motion, its types, parameters and some more.

What is Motion?

Motion is the change in an object's position over time. Whether it's a leaf blowing in the wind, a car moving down the road, or the flow of a river, all these examples demonstrate motion. Even things that seem still, like the air or the molecules inside a solid object, are constantly in motion. The entire universe is in a state of continuous motion, from the smallest particles, like atoms, to the largest cosmic bodies. For example, the cyclists shown in the image are considered to be in motion.

How to Identify an Object in Motion?

To identify an object in motion, compare its position at different times relative to a reference point. Motion occurs when there is a change in position over time, and this change can be quantified using displacement, speed, and velocity. Several things around us move like Earth which appears to be still but is always in motion.

Parameters of Motion

There are four main parameters that affect the motion of the objects they are:

• Distance (d)
• Displacement (s)
• Speed/Velocity (v)
• Time (t)

Distance

Distance is used to refer to the complete path length between any two successive points. The distance is a scalar quantity, with only magnitude and no associated direction. Therefore, the distance is always positive in nature.

The distance of a body gives the descriptive route information being followed by an object from one point to another. The distance is denoted by the symbol 'd' and The distance between points A and B is illustrated in the image below.

Distance Formula,

We know that,

Speed = Distance / Time

Therefore using the above formula we get the formula for the distance when the speed and time of any motion is given is,

Distance = Speed × Time

d = s × t

where,

• d is the Distance Covered Object
• s is the Speed
• t is the Time Taken

Displacement

Displacement is the direct length of the minimum path between any two successive points. Displacement, therefore, may refer to displacement as a vector quantity, with both an associated magnitude and direction. The displacement of an object between any two points is considered to be positive, negative, and even zero.

Displacement is independent of the path and only depends upon the initial and final position of the body.  The displacement between points A and B is shown in the image below. It is denoted by 's'. 

Displacement Formula,

Mathematically, the displacement is defined as, the "Minimum distance between two points." The formula used to find the displacement is,

∆x = x_f - x₀

where,

• x_f is the Final Position of Object
• x₀ is the Starting Position of Object
• ∆x is the Displacement of Object

Speed

Speed can be defined as the rate of change of position of an object moving in any direction. Speed is measured as the ratio of the distance covered by an object to the total time to cover this distance. The speed of a body is considered to be a scalar quantity, with only magnitude and no associated direction.

Speed = Distance / Time

v = d / t

Unit of Speed in different systems is different system as shown below:

CGS system	cm/s
SI system	m/s

Dimensional formula for Speed is [LT^-1].

Velocity

Velocity is defined as the rate of change of displacement per unit time. It is a vector quantity. Velocity is nothing but speed in a particular direction. Hence, the unit and dimension formula of velocity is same as that of speed. Hence, the unit of velocity is m/s and the dimensional formula is [LT^-1]

Time

Time is an important frame of reference to evaluate the change in state and motion of the objects. Time is referred to as the interval over which any object undergoes modifications in its motion, orientation and structure. The criteria for evaluation that time has passed is the modification in any object.

S.I. unit for time is the second, abbreviated as s. It is also measured in other units such as minutes(m), hours(hr), etc. The dimensional formula for time is [T¹].

Types of Motion

The motion of an object depends on the force acting on the body. There are various kinds of motion and different kinds of motion are explained below in this article,

• Linear Motion
• Translational Motion
• Rotational Motion
• Periodic Motion
• Simple Harmonic Motion
• Oscillatory Motion
• Projectille Motion

Now let's learn about them in detail.

Linear Motion

Linear motion is a specific type of translational motion where the body moves only in one single direction. It can be either in the x-direction or in the y-direction or in the z-direction. For example, the motion of ants on the edge of the knife and others.

Translational Motion

In Translational motion, the object is free to move and can move in any of the three (x, y, z) directions. For example, the motion of Areoplane, birds, bees, etc is considered to be translational motion.

Rotational Motion

In Rotational motion, the object moves along a circular path about a fixed axis. For example, the Rotational motion of the Earth, Moon, Top and others is the form of the Rotational Motion.

Periodic Motion

Periodic motion is the type of motion that repeats itself after certain intervals of time. For example, the motion of the Earth around the Sun, the motion of the comments, and the motion of the Moon around the Earth exhibit periodic motion.

Simple Harmonic Motion

Simple Harmonic Motion is a specific type of periodic motion in which the particle moves to and fro around a fixed point. Like in the case of a simple pendulum.

Oscillatory Motion

The to-and-fro motion of an object is called the Oscillatory Motion it is repetitive in nature it repeats itself within a fixed time frame. Mechanical oscillations are called vibrations. For example the motion of the guitar strings and other.

Projectile Motion

When an object has both horizontal displacement as well as vertical displacement then it is said to be in Projectile motion. For example, the movement of the bullet fired from the gun, and a stone thrown in the air also follows the projectile motion.

Also Read, Uniform and Non-Uniform Motion

Types of Motion as Per Directions

There are three types of motion in physics as per the direction of motion that are,

1. One Dimensional Motion
2. Two Dimensional Motion
3. Three Dimensional Motion

Now let's learn about them in detail.

1. One Dimensional Motion

Whenever anyone out of the three coordinate spaces representing the position of the object undergoes any change (shape, speed, distance) with respect to time, then that motion is called one-dimensional motion, or uni-dimensional motion.

Examples of One Dimensional Motion

• The motion of a steel block in a straight line.
• Object freely falling under the effect of gravity.
• A man walking through a straight lane.

2. Two Dimensional Motion

Whenever any pair out of the three coordinate spaces representing the position of the object undergoes any change (shape, speed, distance) with respect to time, then that motion is called two-dimensional motion, or bi-dimensional motion.

Examples of Two Dimensional Motion

• Movement of a train along a zigzag track.
• The rotation of the planets around the sun.

3. Three Dimensional Motion

Whenever all the three coordinate spaces representing the position of the object undergoes any change (shape, speed, distance) with respect to time, then that motion is called three-dimensional motion. The body tends to undergo movement within a planar structure.

Examples of Three Dimensional Motion

• Objects flying in arbitrary paths in the sky.
• The motion of atoms inside a gas molecule.

Also Read,

• Newton's Laws of Motion
• Equations of Motion

Difference Between Periodic and Non-Periodic Motion

The difference between periodic and non-periodic motion can be understood by the following table:

Conclusion

Motion, in physics, refers to the change in an object's position over time. It is a fundamental concept that describes how objects move and interact within the universe. When an object's location changes relative to a reference point, it is considered to be in motion.

You may also Read,

• Force Law for Simple Harmonic Motion
• Difference between Rectilinear Motion and Linear Motion
• Law of Inertia