The object under motion can undergo a change in its speed. The measure of the rate of change in its speed along with direction with respect to time is called acceleration. The motion of the object can be linear or circular. Thus, the acceleration involved in linear motion is called linear acceleration. The acceleration involved in a circular motion is called angular acceleration.

If we recall circular motion. Here distance covered will be along the curved path. (circumference of a circle). The velocity involved is angular velocity and not linear velocity. Similarly, the acceleration involved is centripetal acceleration. Some of the important terms involved are-

Terms |
Definition |
Symbol |
Formula |
Units |

## Angular displacement |
The angular difference between the initial and final position of an object. | 𝜃 | \(\theta =\frac{s}{r}\) | Radian |

## Angular velocity |
The rate of change of angular displacement with respect to time | ⍵ | \(\omega =\frac{d\theta }{dt}\) | radian/sec |

## Angular acceleration |
The rate of change of angular velocity with respect to time | 𝛼 | \(\alpha =\frac{d\omega }{dt}\) | radian/sec^{2} |

In a circular motion, the acceleration experience by the body towards the centre is called the centripetal acceleration. This can be resolved into two component. A radial component and a tangential component depending upone the type of motion.

## Radial Acceleration Definition

In a uniform circular motion, “the acceleration of the object is along the radius, directed towards the center” is called radial acceleration.

## Radial Acceleration Formula

*figure(1) schematic diagram representing an object under rotational motion*

An object A is tied to a string and made to rotate about a fixed point O (centre) (see figure(1)). The object when rotated fast the string (OA) looks almost like the radius of the circle. Which implies that a force is exerted on the object from the centre, thereby an acceleration a_{0} along the radial direction. (along the radius of the circle towards centre). To counter this force, tension is developed along the string in the opposite direction. This force due to tension is called centripetal force, thus the acceleration generated on the object is called centripetal acceleration or radial acceleration a_{r}.

*figure(2) Two positions of object A and B. They are infinitesimally close. *

*figure(3) The equivalent diagram of the centripetal velocity vector A and B.*

Implementing the property of similar triangles we get-

\(\frac{AB}{OA}=\frac{l}{r}\)Since A and B are infinitesimally close we can approximate AB to the length of arc AB \(AB=v\times dt\)

From figure(3) since A and B are very close, \(v+dv\approx dv\) \(\frac{AB}{OA}=\frac{dv}{v}\) \(\frac{v\times dt}{r}=\frac{dv}{v}\)

On rearranging,

\(\frac{dv}{dt}=\frac{v^{2}}{r}\)Thus, \(\frac{dv}{dt}\) gives radial acceleration of an object under uniform circular motion. We arrive at the final expression-

\(a_{r}=\frac{v^{2}}{r}\) |

## Tangential Component

Tangential component is defined as the component of angular acceleration tangential to the circular path. The unit of measurement is m.s^{-2}. The mathematical representation is given as:

\(a_{t}=\frac{v_{2}-v_{1}}{t}\)
Where,

- a
_{t}is the tangential component - t is the time period
- v
_{1}and v_{2}are the respective velocities of the two objects in circular motion

## Radial Acceleration units

Radial Acceleration has the unit same as that of angular acceleration that is radian/sec^{2}

**Physics Related Topics:**

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IS THERE ANY DIFFERENCE between radial acc. and angular acc. ?

Angular acceleration applies to the whole rigid object. However, centripetal acceleration is for a specific radius.