What is translatory motion?
Before one can discuss translator motion, one must first understand the meaning of the term “Motion” from the point of Physics. The question arises as to “when can we say that a body is in motion or is at rest?” In non-professionals terms, one might say that if a body does not change its position with respect to time (or with passage of time), hence the body is at rest. If the same body was moving about, changing positions with respect to time, we say the body is in motion. However, let us imagine a book placed on top of a table. If one was sitting near the table, it can be concluded that the book is at rest, as it is not moving. However, if the same person was observing the same table, sitting on the moon, the conclusion differs because the Earth is moving with respect to the moon (it is changing positions), thus the room too is moving and thereby the book is moving too. Therefore, it can be concluded that the book is in motion. Thus, it needs to be understood that the state of motion or rest is with respect to a reference frame and an observer.
Therefore, Motion is a combined property of an object of our interest and an observer. Thus, the terms “in motion” or “at rest” are meaningless without the presence of an observer. Strictly speaking, nothing is ever at absolute rest or in absolute motion.
Types of motions
There are two kinds of motions, vis Translational motion and Rotational motion. A motion of a body, in which every point of the moving body moves uniformly in the same line or direction, is called as Translational Motion or Translatory Motion. It must be remembered that if a body is under translational motion, then its orientation does not change with respect to a fixed point. For example, a man walking on a street, birds flying in the sky etc. A body, when shifted or moved from point A to Point B is said to experience translational motion. Here, all points of the moving body move uniformly and no change in orientation occurs. A pure translational motion, is one in which all particles of the moving body, move parallel to each other. Therefore, all points of the body possess velocities and accelerations, in the same direction and magnitude, at every instant of time. Every point of this body describes identical trajectories. However, it must be remembered that the orientation remains fixed with respect to a fixed reference and this is the differentiating factor between rotational and translation motion. In rotational motion, the body moves about an axis and thus, orientation changes such as Earth rotating on its axis. In rotational motion, the body travels an angle with change in time, and the motion is described in terms of angular velocity and angular acceleration.
There are two types of translational motion which are:
- Rectilinear Motion
- Curvilinear motion
Rectilinear Motion:
In rectilinear motion, the body is moving in a straight line. For example, a man walking on a street, a bullet shot from a gun. Here, it does not matter whether the motion is uniform or non-uniform. To understand further, consider a car moving from point A to point B on a straight road with some random velocity, v.
The observer can conclude that the motion is rectilinear because the car is moving in a straight line and all the particles of the car are moving at the same speed, parallel to each other in the same direction. There is no change of orientation as well. It should be remembered that the car is being considered in its entirety and wheels form a part of it. Individually, the wheels exhibit rotational and translational motion.
Curvilinear Motion:
In this form of motion, the body must be moving in a curved path. Therefore, the body exhibits motion in 2 or 3 dimensions. This is possible ensuring that while the body moves in a curved path, the body does not change its orientation with respect to time. It can be safely said that every pure translational motion need not always be in a straight line. An example of curvilinear motion is the projection of a ball, say one projects a ball from point A to point B with the maximum height being attained at point C. This motion is called projectile motion which is curvilinear in nature. Here, the ball is allowed to move in a curved path with a certain acceleration and velocity, while ensuring the orientation of the ball remains the same. However, if it was a spinner delivering to the batsman, it would not be curvilinear as he would impart a spin to the ball, which would mean the motion is translational as well as rotational in nature.
Few examples of translational motion are as below:
- person walking from point A to B
- Car or bus moving on a road.
- Ship sailing in the sea.
- Dog walking.
- A coin falling straight towards the surface of the earth