Motion is defined as the change in the position of an object with respect to time i.e. when an object changes its position according to time it is said to be in the state of motion. Everything in the universe is in a state of continuous motion, for example, the moon revolves around the planets, the planets revolve around the sun, the sun revolves around the center of the galaxies, and the galaxies are themselves expanding. Motion is in the syllabus of Class 9 and Class 11. Let’s learn about the motion in physics in detail in this article.
What is Motion?
The change in the position of anybody with respect to time can be termed motion. Any object under motion can be visualized by the naked eye by determining the change in the positional coordinates and then, associating it through the eye of the arbitrary observer. Motion can be computed in terms of both the position vectors, that is, the displacement, and distance, and taking into consideration the speed factors, that is, velocity, acceleration, speed, and time.
For instance, the cyclists in the image given below are said to be in a state of motion.
How to Identify an Object in Motion?
Any movement done by the object can be found by comparing the new position and the original position of the object. The change in the position of the object, with respect to time, is considered motion. Several things around us move like Earth which appears to be still but is always in motion. The car, bikes, people, and other things around us also move.
Parameters in 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. Since the distance between two points is equivalent to the path length, it can be measured across different trajectories, that is, linear or zigzag paths. The distance is denoted by the symbol ‘d’.
Distance = Speed × Time
d = v × t
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. Therefore, it does not provide complete information on the route. Displacement is always indicated with an arrow. It is denoted by ‘s’.
Displacement = Velocity × Time
s = v × t
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.
Types of Motion as per State of Motion
There are two types of Motion on the basis of State of Motion
- Uniform Motion
- Non-Uniform Motion
Now let’s learn about them in detail.
Uniform Motion
The uni-dimensional motion of an object where it travels with uniform speed all along the path is called Uniform motion. Since the body covers equal distances in equal intervals of time, the velocity of the body remains constant. The speed of an object remains the same during all time frames, the average speed of the object is equivalent to its actual speed. No acceleration is attained by the object in the case of uniform motion. For instance, a car travelling 20 km in the first hour, 20 km in the next hour, and so on continue with this throughout its motion.
Examples of Uniform Motion
Various examples of the objects performing the uniform motion are,
- The hands of the clock cover equal distances.
- A car going along a straight level road at a steady speed.
- An aeroplane flying at a steady speed in the air.
Non-Uniform Motion
The uni-dimensional motion of an object where it travels with a varying speed all along the path is called Non-Uniform motion. Since the body covers unequal distances in equal intervals of time, the velocity of the body remains modified. The speed of an object changes during the time frames, and the average speed may be different from its actual speed. Acceleration or deceleration is attained by the object in the case of non-uniform motion. For instance, a car travelling 20 km in the first hour, 30 km in the next hour, and so on. Continuing with a varying speed throughout its motion.
Examples of Non-Uniform Motion
Various examples of the objects performing the non-uniform motion are,
- A racing car
- A ball bouncing at different intervals
- Two cars colliding with each other
Types of Motion as Per Directions
There are three types of motion in physics as per the direction of motion that are,
- One Dimensional Motion
- Two Dimensional Motion
- Three Dimensional Motion
Now let’s learn about them in detail.
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
Examples of One Dimensional Motion are,
- 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
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
Examples of Two Dimensional Motion are,
- Movement of a train along a zigzag track.
- The rotation of the planets around the sun
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
Examples of Three Dimensional Motion are,
- Objects flying in arbitrary paths in the sky.
- The motion of atoms inside a gas molecule.
Laws of Motion
Laws of motion also known as Newton’s Laws of Motion are the basic laws that help us to understand the motion of any object. These laws are valid for each inertial frame of reference. The three laws of motion are:
First Law of Motion: Also known as Newton’s First Law of Motion states that an object stays in an existing state of motion or rest unit unless a net external force is applied to it.
Second Law of Motion: Also known as Newton’s Second Law of Motion states that the change in momentum of the object with respect to time is equal to the net force applied.
Third Law Motion: Also known as Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction.
Equations of Motion
There are three equations of motion. These are mentioned below:
First Equation of Motion: It is used to find the final velocity of an object if its initial velocity, acceleration and time is given. Mathematically it is represented as v = u + at
Second Equation of Motion: It is used to find the distance if the initial velocity, acceleration and time is given. Mathematically it is given as s = ut + 1/2at2
Third Equation of Motion: In this equation, the difference of squares of final and initial velocity is equal to twice the product of acceleration and distance. Mathematically it is given as v2 – u2 = 2as
Differentiate Between Periodic and Non-Periodic Motion
The difference between periodic and non-periodic motion can be understood by the following table:
| Periodic Motion | Non-Periodic Motion |
|---|---|
| In periodic motion, the same path is followed after a fixed time interval. | In non-periodic motion, the path followed by the object is not fixed and can be random. |
| The position of the object after a specific period of time can be guessed. | The position of the object after a specific period of time cannot be guessed. |
| Examples: Oscillatory motion, Motion of planets around the sun, etc. | Examples: The motion of vehicles, the motion of bees, etc. |
Also, Check,
- Force Law for Simple Harmonic Motion
- Difference between Rectilinear Motion and Linear Motion
- Law of Inertia
FAQs on Motion
1. What is Motion in Physcis?
The motion of an object is defined as the change in its position with respect to the time taken.
2. What are Types of Motion?
Motion of the object can be divided into various categories some of the types of motion are,
- Linear Motion
- Translational Motion
- Rotary Motion
- Oscillatory Motion
3. What are Examples of Motion?
Various examples of motion are,
- A child playing in the swing exhibited motion.
- The movement of bees around the flower.
- A running athlete shows motion, etc.
4. What is Periodic Motion?
In periodic motion, the motion repeats itself after certain intervals of time. Example: Motion of Earth around Sun, Motion of blades of the fan, etc.
5. What is Translation Motion?
Translational motion is the motion by which a body shifts from one point in space to another. Translational motion encompasses both rectilinear and curvilinear motion of the objects. Every component of the body moves through the same portion in case of these motions. For instance, a bullet fired through a gun.
6. What is Rotational Motion?
When an object moves along a circular path about a fixed axis this motion is called Rotational Motion. Example: motion of Earth along its axis, the motion of the top, etc.
7. What is Oscillatory Motion?
If an object moves to and fro around a fixed point, then its motion is called Oscillatory Motion. Examples: motion of the pendulum, the motion of the guitar string and others.
8. What is Uniform Motion?
An object is said to be in uniform motion if it covers equal distance in equal interval of time.
9. What is Difference between Curvilinear Motion and Rectilinear Motion?
Difference between Curvilinear Motion and Rectilinear Motion are:
Curvilinear Motion Rectilinear Motion When an object moving in translational motion follows a curved path. An object moving in translation motion opts for a straight-line path. The velocity of the object changes with change in direction The body travels with uniform velocity. Example: A stone thrown up in the air Example: A train moving on a straight track or a car moving on a straight road
Force Law for Simple Harmonic Motion
Have you ever wondered why, when we stretch an elastic band and then let it go, it returns to its previous state? It is compelled to revert to its original state by a force. But what exactly is this force? Let us investigate this force and develop the force law for simple harmonic motion.
Periodic Motion is something we’re already familiar with. Periodic motion is defined as motion that repeats itself at equal intervals of time. For example, the motion of a clock’s hands, the motion of a car’s wheels, and the motion of a merry-go-round. In nature, all of these motions are repeated. They repeat themselves after a certain period of time.
An Oscillatory Motion is a periodic movement in which an item oscillates about its equilibrium position. After a given amount of time, the item repeats the same sequence of moves. An Oscillation is one such series of motions. An oscillatory motion may be seen in the movement of a basic pendulum, the movement of leaves in a breeze, and the movement of a cradle.
Simple Harmonic Motion (SHM)
Simple harmonic motion is the most basic type of oscillatory motion. When an object moves in a straight path, it exhibits simple harmonic motion. All oscillatory motion examples are instances of basic harmonic motion.
Let’s now discuss some important terms related to a Simple Harmonic Motion of a particle as
Displacement (x): Displacement at any instant of time is defined as the net distance travelled by the body executing SHM from its mean or equilibrium position.
Amplitude (A): The amplitude of oscillation is defined as the maximum displacement of the body executing SHM on either side of the mean position.
Velocity (v): Velocity at any instant is defined as the rate of change of displacement with time. For a body executing SHM, its velocity is maximum at the mean position and minimum (zero) at the extremes. The Velocity of the body is inversely proportional to the displacement from the mean position.
Acceleration (a): Acceleration is defined as the rate of change of velocity with time. Unlike velocity, acceleration is directly proportional to displacement. It is maximum at the extreme positions where the displacement is maximum and minimum at the mean position (displacement = 0).
Restoring Force (FR): Restoring Force is the force that always acts in a direction opposite to that of displacement but is directly proportional to it. Restoring Force is maximum at the extreme positions and minimum at the mean position.
Spring Constant (k): Spring Constant is a constant value for a particular spring that determines the amount of force required to compress or stretch the spring by 1 unit.
Energy (E): The total energy of the body under SHM is called mechanical energy, mechanical energy of the body remains constant throughout the motion if the medium is frictionless. The Mechanical Energy of a body at any instant is the sum total of its kinetic and potential energy.
Time Period (T): The Time Period of oscillation is defined as the time taken by the body to complete one oscillation. In other words, it is the time taken to cover 4 times the amplitude.
Frequency (f): Frequency is defined as the number of oscillations made by the body in one second. It is reciprocal of the time period. f = (1/T)
Difference between Rectilinear motion and Linear motion
Read Discuss
The free movement of an object in relation to time is known as motion. It can be described as the act of shifting one’s position. For instance, a moving train, a rotating fan, a rolling ball, and so forth. Even though the planet is always in motion, there are several sorts of motion that will help you grasp things more thoroughly.
The motion of an object is categorized into four, on the basis of the nature of the movement of the object as,
- Rotatory Motion – It is a type of motion in which an object rotates around a central axis. Consider the case of a revolving fan.
- Oscillatory Motion – In oscillatory motion, an object moves back and forth in the same motion. Consider the pendulum.
- Linear Motion – This is a one-dimensional motion that occurs in a straight line. for example, a train on a track.
- Reciprocating motion – A continuous up-and-down or back-and-forth motion is referred to as a reciprocating motion. A gymnast, for example, swinging on a ring.
However, on the basis of the path followed by the object, the motion is described in two ways:
- Rectilinear Motion – A straight-line path of motion. All particles in this motion go the same distance in a parallel straight line.
- Curvilinear Motion – A curved line path of motion. The body’s orientation in space remains constant, but the trajectories of individual particles are curved.
- What is Linear Motion?
- Examples of Linear Motion:
- Athletes running along the straight line.
- Skating or swimming done by any person possesses linear motion.
- Types of Linear Motion
- Uniform Motion – When a body moves in a straight path at a consistent speed, it is said to be in uniform motion. For example, consider an automobile driving at a constant pace down a straight route. A straight line can be used to indicate uniform motion in a graphical representation.
- Non-Uniform Motion – When a body travels the same distance in the same amount of time, it is said to be in non-uniform motion. This motion can be depicted as a curved line in the pictorial form.
- What is Rectilinear Motion?
- Examples of Rectilinear Motion:
- Falling of objects from a certain height.
- Ants moving in a straight line.
- Moving of train on track.
- Falling of stone from the top of the building to reach the ground.
- Difference between Linear Motion and Rectilinear Motion:
- Sample Questions:
- Question 1: What are the two types of linear motion?
- Answer:
- Question 2: Does motion have any units.
- Answer:
- Question 3: A man is moving in a car with a velocity of 8 m/s, then he suddenly stops the car. Does he brake to stop completely with an acceleration of -4m/s2?