 # Introduction to Motion

Everything in this universe is in the state of continuous movement. You can find objects moving everywhere. The motion of animals and humans are everyday examples of motion. The basic particle of a matter, i.e., the atom is in the state of continuous motion too. Every single physical procedure in this universe is made up of some type of motion. It can be either slow or fast, but the motion is present.

So, how do you define that there is movement in an object? You identify any movement in the object when you compare its new position from the original position. Any change in the position of the object, with respect to time, is considered to be a motion. There are several things that you can see moving while certain objects like Earth that appear to be still, is also in motion in an actual sense. Everything on Earth that appears still is actually in motion as the Earth itself is in motion (i.e, Rotation and Revolution)

What is Motion?

A book that falls from a table, water flowing from the tap, or rattling windows, all these are the examples of motion. Let us see some important terms that will help us in determining motion.

•  Distance
•  Speed
•  Displacement
•  Time

• Both distance as well as displacement help in describing the change in the object’s position. The distance covered by an object from point A to point B depends on the type of path it has taken. So, if an object takes a circular path, then the distance covered by it on this path will be different from the distance covered in case of a linear path.
In the case of displacement, it is defined as the shortest distance that connects the two points, A and B (basically initial and final point).

So, let us say A and B are two cities. The distance between them is ‘d’. Now, when a person moves from city A to city B and then again returns back to city A, then

Distance traveled = d (From A to B) + d (From B to A)

Displacement = 0, as there is no difference in the initial and final position of the person. He started from A and returned back to A. So, in this case, displacement is nil.

Speed is the rate at which the position of the object changes with respect to its origin. It is measured as distance (in meters)/ Time (in seconds).

Types of Motion

Now, let us talk about the different types of motions that can be seen in an object. These are Linear, Rotary, Oscillating motion, and Periodic motion. Each of these types is achieved with a different mechanical means. Let us learn more about them in detail.

1) Linear Motion

In linear motion, the object moves from one position to another in either a curved path or a straight line. On the basis of the type of path taken by an object, linear motion is further classified as:

• Rectilinear Motion – Here, the path taken by an object is a straight line.

• Curvilinear Motion – Here, the path taken by the object is curved.

• One of the best examples of linear motion is linear actuators where you can find cars, cycles, trains and other vehicles travelling in one straight direction. But it will not be called as a linear motion when the road or rail track is perfectly circular. You can even find linear cylinders that display linear motion in pneumatic, hydraulic and electric options. A linear motion has a lot of significance in the field of manufacturing, automation, robotics, etc.

2) Rotary Motion

Rotary motion is a kind of motion where the object moves in a circle. This type of motion occurs when an object rotates at its own place or axis. The rotary motion was the first type of motion that was invented by scientists in primitive times.

• Earth rotating on its own axis about the sun is the best example of rotary motion.

• Another example is the movement of the wheels and steering wheel of the car in the driving state. You will find that both are rotating around their own axis. The same thing goes with the engine of the car as it also moves on its own place.

• Similar to linear cylinders, nowadays rotary actuators are extensively used in various industries. These cylinders come in pneumatic, electric, and hydraulic options.

3) Oscillatory Motion

This is the third type of motion that is characterized by the movement of the object in the form of front and back oscillation. In other words, an oscillatory motion is defined as the movement of an object around its mean position. If an object repeats the cycle of its motion after a specific time period, then it is regarded as an oscillating motion.
One of the best examples of oscillating motion is the pendulum of a clock. It repeats its motion after a certain time frame. In actual sense, the pendulum is not displacing from its position. It is stationary in one position, yet it displays motion. Such type of recurring motion after a certain time period is called an oscillating motion.
In this kind of motion, the movement of the object is termed as oscillation. This is because of the repeated nature of the motion that takes place after a set time period. A few other illustrations of an oscillating motion are:

• When a child oscillates to and fro around its fixed position on the swing.

• Table fan is another example of periodic motion.

• Both linear, as well as a rotary actuator, has oscillating motion.

• Sound waves are the result of oscillation of particles.

• When the cords of the sitar or guitar are struck, then they move to and fro about their mean position (i.e, oscillatory motion).

• 4) Periodic Motion:

Periodic motion is a type of motion that is repeated at equal time intervals. A few examples of this motion is a bouncing ball, a rocking chair, a swing in motion, a water wave, a vibrating tuning fork etc.