# 19.4 Understanding rolling motion

 Page 1 / 4
Pure rolling is governed by Newton's laws as applicable to pure translation and pure rotation under the condition of rolling.

Essentials of pure rolling motion are no different than that of pure translational and rotational motions, except that these two basic forms of motions occur simultaneously. A clear understanding of the two basic motion forms, therefore, is a perquisite for a clear understanding of pure rolling motion (referred simply as rolling also).

There are two distinct framework associated with the study of rolling motion :

• Uniform rolling
• Accelerated rolling

## Independence of analysis

Rolling, being combination of translation and rotation, involves two “causes”, which might change its velocity. Two causes act to produce “effects” independently, but in tandem to satisfy the condition of rolling (we shall subsequently derive this condition in the module).

A net force causes acceleration of the center of mass of the rigid body. A rolling motion involves rigid body of finite size and, therefore, its translation should always be referred to the center of mass. Further, when we consider the effect of force, we treat translation as if the rigid body were not rotating at all.

Similarly, a net torque causes rotational acceleration of the rigid body about its central axis passing through center of mass. When we consider the effect of torque, we treat rotation as if the axis of rotation were not translating at all.

In simple words, the analysis of rolling can be done independently for two motions types as if other motion did not exist. This independence of analysis of motion allows us to apply the familiar laws of motion for analyzing each motion types. We are required only to combine the results to describe rolling motion.

## Force and torque

Treatment of force with respect to a rigid body capable of both translation and rotation is different than the case when only one type of motion is involved (i.e. not the combination). In pure translation along a straight line, the rigid body is constrained (or otherwise) not to rotate; similarly in pure rotation about a fixed axis, the rigid body is constrained not to translate.

A force, whose line of action passes through center of mass, is capable to produce only translational acceleration ( ${a}_{C}$ ). A force, whose line of action does not pass through center of mass, works as “force” to produce translational acceleration ( ${a}_{C}$ ) and simultaneously as “torque” to produce angular acceleration (α).

Since there may be multiple effects (more than one) of a single force, it is always desirable to clearly understand the roles of the forces operating on the rolling body to accurately analyze its motion.

## Rolling and newton’s first law

A pure rolling is equivalent to pure translation and pure rotation. It, therefore, follows that a uniform rolling (i.e. rolling with constant velocity) is equivalent to uniform translation (constant linear velocity) and uniform rotation (constant angular velocity).

#### Questions & Answers

List the application of projectile
How can we take advantage of our knowledge about motion?
pls explain what is dimension of 1in length and -1 in time ,what's is there difference between them
what are scalars
show that 1w= 10^7ergs^-1
what's lamin's theorems and it's mathematics representative
if the wavelength is double,what is the frequency of the wave
What are the system of units
A stone propelled from a catapult with a speed of 50ms-1 attains a height of 100m. Calculate the time of flight, calculate the angle of projection, calculate the range attained
58asagravitasnal firce
Amar
water boil at 100 and why
what is upper limit of speed
what temperature is 0 k
Riya
0k is the lower limit of the themordynamic scale which is equalt to -273 In celcius scale
Mustapha
How MKS system is the subset of SI system?
which colour has the shortest wavelength in the white light spectrum
how do we add
if x=a-b, a=5.8cm b=3.22 cm find percentage error in x
x=5.8-3.22 x=2.58