# How to Calculate Angular Velocity in Radians per Second

## What is Angular Velocity?

Angular velocity is a fundamental concept in physics that describes the rate at which an object rotates or moves around a central point or axis. It measures how quickly an object is changing its angular position with respect to time.

## Angular Velocity Symbol and Unit

The angular velocity symbol is typically denoted by the Greek letter omega (ω). The angular velocity units is expressed in units such as radians per second (rad/s) or degrees per second (°/s).

## Angular Velocity Formula

Mathematically, angular velocity (ω) is defined as the change in angular displacement (θ) divided by the change in time (t):

ω = Δθ / Δt

Where:

• Δθ represents the change in angular displacement, often measured in radians (rad).
• Δt is the change in time, usually measured in seconds (s).

Angular velocity can be either positive or negative, depending on the direction of rotation. A positive angular velocity indicates counterclockwise rotation, while a negative angular velocity indicates clockwise rotation.

Angular velocity is a very important concept in many areas of physics, including mechanics, kinematics, and rotational dynamics, and it plays a significant role in describing the motion of objects that undergo circular or rotational motion.

## How to Calculate Angular Velocity

Angular velocity can be calculated using the following formula: ω = Δθ / Δt

where:

• Δθ is the change in angular displacement in radians (Δθ = θ_final – θ_initial).
• Δt is the change in time in seconds.

## Solved Problems: How to Find Angular Velocity

Here is how to calculate angular velocity in radians per second:

### Problem 1

A stone whirled at the end of a rope 50 centimetres long, makes 8 complete revolutions in 4 seconds. Calculate the angular velocity in radians per second.

Solution

Data:

One complete revolution makes an angle θ = 3600

and θ = 3600 is the same thing as 2π radians

[where π =1800 and 2 x 1800 = 3600]

Therefore,

The time for 8 complete revolutions = 4 seconds

we can now calculate the angular velocity by applying the formula that says

Angular velocity,  ω = θ/t

By substituting our data into the above formula, we will get

Angular velocity,  ω = θ/t = 16π radians/4 seconds

We will now have ω = 4 π radians/seconds or 4π rad/s

Therefore, the angular velocity is 4π radians per second.

### Problem 2

An object is moving along a circular path with a radius of 4 meters and a linear velocity of 16 meters per second. Determine the angular velocity of the object in radians per second.

Solution

Data:

Speed, v = 16 m/s

angular velocity =?

and the formula for calculating the angular velocity is

Angular velocity,  ω = v/r

We can now substitute our data into the above formula

Angular velocity,  ω = 16/4 = 4 radians per second or 4 rads-1

Therefore, the angular velocity of the object is 4 radians per second.

### Problem 3

A wheel is rotating at an angular velocity of 3 radians per second. If it continues to rotate at this rate for 10 seconds, how much angular displacement does it undergo during this time?

Solution:

We can use the formula for angular displacement:

Angular Displacement (θ) = Angular Velocity (ω) × Time (t)

Therefore, θ = ω × t

Which shows that θ = 3 rad/s × 10 s

So, the wheel undergoes an angular displacement of 30 radians during the 10 seconds of rotation.

### Problem 4

A fan blade is spinning at an angular velocity of 120 degrees per second. How many complete revolutions does the fan blade make in 30 seconds?

Solution:

To find the number of complete revolutions, we first need to convert the angular velocity from degrees per second to radians per second since there are 2π radians in one complete revolution.

So, to convert from degrees to radians, we use the conversion factor:

Angular Velocity (in radians per second) = 120 degrees/second × (π/180 radians/degree)

Now, we can calculate the number of complete revolutions in 30 seconds:

Therefore, number of Revolutions = (Angular Velocity × Time) / (2π)

The number of Revolutions = [(2π/3) rad/s × 30 s] / (2π)

Number of Revolutions = (20/3) revolutions

So, the fan blade makes approximately 6.67 complete revolutions in 30 seconds.

## Key points about angular velocity

1. Units and Dimensions: Angular velocity is typically measured in radians per second (rad/s) in the International System of Units (SI). The radian is a unit of angle measurement, and one radian is the angle subtended at the center of a circle by an arc that has a length equal to the radius of the circle. Angular velocity has dimensions of [T]^-1, where [T] represents time.
2. Direction: Angular velocity is a vector and has a direction. The direction of angular velocity is perpendicular to the plane of rotation, following the right-hand rule. This means that if you curl the fingers of your right hand in the direction of rotation, your thumb points in the direction of the angular velocity vector.
3. Constant vs. Variable Angular Velocity: An object with a constant angular velocity is rotating at a uniform rate, covering equal angular displacements in equal time intervals. In contrast, an object with a variable angular velocity is changing its rate of rotation over time.
• Δθ is the change in angular displacement in radians (Δθ = θfinal – θinitial).
• Δt is the change in time in seconds.
4. Relationship with Linear Velocity: Angular velocity is related to linear velocity (the velocity of a point on the edge of a rotating object) by the formula: v = ω * r

This relationship between angular velocity and linear velocity is crucial when understanding rotational motion, as it allows you to connect the speed of rotation to the linear speed of points on a rotating object, such as the edge of a wheel or the outer edge of a turntable.

Angular velocity plays a significant role in various fields of physics and engineering, such as mechanics, fluid dynamics, and robotics, as it helps describe and analyze the behavior of rotating systems and their components.

You may also like to read:

How to Calculate Centripetal Force

Reference

Wikipedia