# Rigid Bodies Translational Motion and Rotational Motion

## Introduction

The rigid body is considered as translational zero or negligible deformation. It is also determined as the body that has continuous mass distribution. The rigid body basically has 2 different types of motions that are translational motion and rotational motion. The rigid body when travelling with these types of motions is travelling with displacement in an equal time interval. In the case of the transitional motion the body will travel with same displacement in an equal time interval and in other cases that as rotational motion the body will travel with the same angular displacement in an equal time interval.

## What do you understand by a rigid body and its rotation and motion?

The rigid body is demonstrated as the idealization of a body that does not change its shape or does not deform. It can also be described as particles collection with the property where the distance between particles is unchanged at the time of course of motions of the body. All bodies get deformed when they are in motion (springer, 2019).

In the case of the rigid body there is no deformation is found and is determined as the constant distribution of mass. This can also be explained as when the distance between 2 provided points of the rigid body remains in the constant state in time interval even if an external force is exerted on that body (Schmelzbach et al. 2018).

Even if the rigid body has various mad molecules and atoms they will remain in the uniform motion state. If a rigid body is found in pure rotational motion then it will rotate around an axis that is fixed and perpendicular to a fixed plane.

## What is the translational motion of the rigid body?

There are two major types of the motions of the rigid body the rotational motion and the translational motion. If a rigid body is found travelling along a straight line or even along a linear path then it can be determined as in its translational motion. The translational motion has -1 dimensional motion.

Figure 1: Transitional motion of Rigid Body

In the above-left figure, it can be seen that when on a box an external force is exerted it starts moving along the linear path or the straight line and have a translational motion. In the right figure, the box is being pushed down and it is travelling along the inclined plane and also has translational motion (Cruz et al. 2019).

But here as the box is falling (down) freely then the distance between 2 constituent particles in the body is always fixed and the motion of each rigid body will remain the same to the motional of the entire body translational motion.

## What is the rotational motion of a rigid body?

If a rigid body travels along the circular or curved plane then its centre of mass will remain in motion and the rigid body will be in rotational motion. The rigid body that is in rotational motion travels around an axis and the axis is determined as the axis of rotation.

Figure 2: Rotational motion of Rigid Body

From the above figure, it can be seen the rotational motion of a wheel is passing around its axis through the centre. When this wheel is moving around the axis it passes through its centre normally and the entire rigid body and its constituent particles keep rotating along its axis (Kim et al. 2018). The wheel that traces circular path on the axis is determined to be in the rotational motion.

## State the difference between rotational motion and translational motion

Translational motionRotational motion

Here the rigid body moves in the linear path or a straight line

Here the rigid body travels in the curved or circular path.

The rigid body has the same displacement in equal time intervals.

The rigid body has same angular displacement in equal time intervals (Witherspoon et al. 2017).

Pure translational motion takes place when the force is exerted through the centre of mass.

Pure rotational motion takes place when the force is exerted opposite and equally on the body that is distant apart.

Here the centre of mass remains in motion

Here the centre of mass remains fixed.

Table : Differences between rotational motion and translational motion

## Conclusion

If a body is found to change its position and orientation constantly with time is considered to be in motion. The rigid bodies can be in different motions like the translational motion and the rotational motion. When a rigid body is travelling along a straight line then it is considered to be in translational motion. When a rigid body is found travelling along an inclined plane then it is considered to be in rotational motion. If the orientation of the bodies keeps changing continuously with the time interval then it can be determined as the phenomenon of rotation.

## FAQs

Q1. What are the translational motion and its types?

The translational motion is described as the motion of a body in which all points of the moving body that is travelling in the same direction or line uniformly. In translational motion the different object points never change the orientation to each other. There are various types of translational motion such as, Rectilinear motion, and Curvilinear motion.

Q2. What do you mean by Rectilinear motion, and Curvilinear motion?

Rectilinear motion, is one of the parts of the translational motion, where the body travels in a linear path and acceleration remains in a uniform state. The Curvilinear motion, is another part of the translational motion and here the body travels along a curved plane and the acceleration varies in this motion.

Q3. What are the differences between linear and non-rigid bodies?

If force is exerted on a rigid body then there will be a change in the state of motion of body and if the force is exerted on a non-rigid body then the size and shape of the body will get changed. The rigid body has well-defined unique equilibrium geometry, whereas the non-rigid body has no possible unique equilibrium geometry.

Q4. What is axis of rotation?

The axis around which the body keeps rotating either in a circular path is called the axis of rotation. In the dynamics and kinematics of rotation of rigid body that takes place around an axis that is fixed is determined to be fully analogous to those of linear motion along one fixed direction and is in the rotational motion.

Updated on: 13-Oct-2022

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