Browse Definitions :
Definition

radian per second (rad/s or rad/sec)

The radian per second (symbolized rad/s or rad/sec) is the Standard International ( SI ) unit of angular (rotational) speed. This quantity can be defined in either of two senses: average or instantaneous.

Average angular speed is obtained by measuring the angle in radian s through which an object rotates in a certain number of seconds, and then dividing the total angle by the time. If u avg represents the average angular speed of an object (in radians per second) during a time interval t (in seconds), and the angle through which the object rotates in that time is equal to q (in radians), then:

u avg = q / t

Instantaneous angular speed is more difficult to intuit, because it involves an expression of motion over an "infinitely short" interval of time. Let p represent a specific point in time. Suppose an object is in rotational motion at about that time. The average angular speed can be measured over increasingly short time intervals centered at p , for example:

[ p -4, p +4]
[ p -3, p +3]
[ p -2 , p +2]
[ p -1, p +1]
[ p -0.5, p +0.5]
[ p -0.25, p +0.25]
.
.
.
[ p - x , p + x ]
.
.
.

where the added and subtracted numbers represent seconds. The instantaneous angular speed, u inst , is the limit of the measured average speed as x approaches zero. This is a theoretical value, because it cannot be obtained except by inference from measurements made over progressively shorter time spans.

It is important to realize that angular speed is not the same thing as angular velocity. Angular speed is a scalar (dimensionless) quantity, while angular velocity is a vector quantity consisting of angular speed and direction in the form of a rotational sense (clockwise or counterclockwise). We might say the earth rotates at at 7.272 x 10 -5 rad/s, and this tells us its angular speed. Or we might say the earth rotates at at 0.00007272 (7.272 x 10 -5 ) rad/s counterclockwise relative to the sun as viewed from above the north geographic pole; this tells us the earth's angular velocity. As with angular speed, we might specify either the average angular velocity over a period of time, or the instantaneous angular velocity at an exact moment in time.

In the case of the earth, the instantaneous angular velocity is essentially constant, and it can be said that u inst = u avg . In the case of a moving car or truck, the angular speeds of the wheels, axles, and drive shaft often change, and the statement u inst = u avg is, in general, not true.

Also see radian , second , radian per second squared , and Standard International ( SI ) System of Units.

This was last updated in March 2011

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • Whistleblower Protection Act

    The Whistleblower Protection Act of 1989 is a law that protects federal government employees in the United States from ...

  • smart contract

    A smart contract, also known as a cryptocontract, is a computer program that directly controls the transfer of digital currencies...

  • risk map (risk heat map)

    A risk map, also known as a risk heat map, is a data visualization tool for communicating specific risks an organization faces. A...

SearchSecurity

  • buffer underflow

    Buffer underflow, also known as buffer underrun or buffer underwrite, is a threat to data that typically occurs when the ...

  • digital signature

    A digital signature is a mathematical technique used to validate the authenticity and integrity of a message, software or digital...

  • denial-of-service attack

    A denial-of-service attack is a security event that occurs when an attacker prevents legitimate users from accessing specific ...

SearchHealthIT

SearchDisasterRecovery

  • virtual disaster recovery

    Virtual disaster recovery is a type of DR that typically involves replication and allows a user to fail over to virtualized ...

  • tabletop exercise (TTX)

    A tabletop exercise (TTX) is a disaster preparedness activity that takes participants through the process of dealing with a ...

  • risk mitigation

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a data center.

SearchStorage

  • secondary storage

    Secondary storage is storage for noncritical data that does not need to be frequently accessed.

  • Pure Storage

    Pure Storage is a provider of enterprise data flash storage solutions designed to substitute for electromechanical disk arrays.

  • yobibyte (YiB)

    A yobibyte (YiB) is a unit of measure used to describe data capacity as part of the binary system of measuring computing and ...

Close