# How to Calculate Angular Acceleration

### Article: How to Calculate Angular Acceleration

Angular acceleration is a measure of how quickly an object changes its angular velocity. It occurs in any situation where an object is rotating or moving in a circular path and the rate of rotation is changing. The concept of angular acceleration is crucial in various fields such as physics, engineering, mechanical design, and even in day-to-day applications like the motion of wheels or fans.

#### What is Angular Acceleration?

Angular acceleration is defined as the rate of change of angular velocity with respect to time. It is analogous to linear acceleration but for rotational motion. While linear acceleration is concerned with the change of velocity in a straight line, angular acceleration deals with rotational speed changes.

The SI unit for angular acceleration is radians per second squared (rad/s²).

#### Formula for Angular Acceleration

The angular acceleration ($$\alpha$$) can be calculated with the following formula:

$\alpha = \frac{\Delta \omega}{\Delta t}$

where:
– $$\alpha$$ is the angular acceleration,
– $$\Delta \omega$$ is the change in angular velocity, and
– $$\Delta t$$ is the change in time.

If the angular acceleration is constant, the equation can be rewritten as:

$\alpha = \frac{\omega_f – \omega_i}{t_f – t_i}$

where:
– $$\omega_f$$ is the final angular velocity,
– $$\omega_i$$ is the initial angular velocity,
– $$t_f$$ is the final time, and
– $$t_i$$ is the initial time.

#### Calculating Angular Acceleration Step by Step

To calculate angular acceleration, follow these steps:
1. Determine the initial angular velocity ($$\omega_i$$) of the object.
2. Measure the final angular velocity ($$\omega_f$$) of the object after a period of time.
3. Note the time period ($$\Delta t = t_f – t_i$$) during which the change in angular velocity occurred.
4. Use the formula $$\alpha = \frac{\omega_f – \omega_i}{\Delta t}$$ to find the angular acceleration.

#### Example Problems and Solutions

**Problem 1:**
A wheel accelerates from rest to an angular velocity of 10 rad/s in 5 seconds. Calculate its angular acceleration.

**Solution:**
Initial angular velocity, $$\omega_i = 0$$ rad/s (at rest),
Final angular velocity, $$\omega_f = 10$$ rad/s,
Time taken, $$\Delta t = 5$$ s.

Using the formula:
$\alpha = \frac{\omega_f – \omega_i}{\Delta t} = \frac{10 \text{ rad/s} – 0}{5 \text{ s}} = 2 \text{ rad/s}^2$
Angular acceleration is $$2 \text{ rad/s}^2$$.

**Problem 2:**
A fan blade goes from an angular velocity of 20 rad/s to a stop in 4 seconds. What is the angular acceleration?

**Solution:**
Initial angular velocity, $$\omega_i = 20$$ rad/s,
Final angular velocity, $$\omega_f = 0$$ rad/s (at rest),
Time taken, $$\Delta t = 4$$ s.

$\alpha = \frac{\omega_f – \omega_i}{\Delta t} = \frac{0 – 20 \text{ rad/s}}{4 \text{ s}} = -5 \text{ rad/s}^2$
Angular acceleration is $$-5 \text{ rad/s}^2$$.

**Problem 3:**
A bicycle wheel has an initial angular velocity of 15 rad/s and an angular acceleration of 3 rad/s². What is the angular velocity after 6 seconds?

**Solution:**
Initial angular velocity, $$\omega_i = 15$$ rad/s,
Angular acceleration, $$\alpha = 3 \text{ rad/s}^2$$,
Time, $$t = 6$$ s.

We will use the relationship:
$\omega_f = \omega_i + \alpha t = 15 \text{ rad/s} + (3 \text{ rad/s}^2)(6 \text{ s}) = 15 \text{ rad/s} + 18 \text{ rad/s} = 33 \text{ rad/s}$
Final angular velocity is 33 rad/s.

**Problem 4:**
A rotating disk takes 8 seconds to speed up from 5 rad/s to 25 rad/s. What is the angular acceleration?

**Solution:**
$\alpha = \frac{\omega_f – \omega_i}{\Delta t} = \frac{25 \text{ rad/s} – 5 \text{ rad/s}}{8 \text{ s}} = \frac{20}{8} = 2.5 \text{ rad/s}^2$

**Problem 5:**
A turntable slowing down goes from 33 rad/s to 18 rad/s in 3 seconds. Find the angular acceleration.

**Solution:**
$\alpha = \frac{\omega_f – \omega_i}{\Delta t} = \frac{18 \text{ rad/s} – 33 \text{ rad/s}}{3 \text{ s}} = -5 \text{ rad/s}^2$

**Problem 6:**
A spinning top increases its speed from 0 to 60 rad/s in 2 seconds. What is the angular acceleration?

**Solution:**
$\alpha = \frac{60 \text{ rad/s} – 0}{2 \text{ s}} = 30 \text{ rad/s}^2$

**Problem 7:**
A Ferris wheel accelerates from an angular velocity of 2 rad/s to 6 rad/s in 10 seconds. Calculate the angular acceleration.

**Solution:**
$\alpha = \frac{6 \text{ rad/s} – 2 \text{ rad/s}}{10 \text{ s}} = 0.4 \text{ rad/s}^2$

**Problem 8:**
A drill takes 0.5 seconds to reach an angular velocity of 200 rad/s from rest. What is the angular acceleration?

**Solution:**
$\alpha = \frac{200 \text{ rad/s} – 0}{0.5 \text{ s}} = 400 \text{ rad/s}^2$

**Problem 9:**
Calculate the angular acceleration of a wheel experiencing a change in angular velocity from 50 rad/s to 30 rad/s in 4 seconds.

**Solution:**
$\alpha = \frac{30 \text{ rad/s} – 50 \text{ rad/s}}{4 \text{ s}} = -5 \text{ rad/s}^2$

**Problem 10:**
The angular velocity of a carousel increases from 0.2 rad/s to 1 rad/s in 16 seconds. Find the angular acceleration.

**Solution:**
$\alpha = \frac{1 \text{ rad/s} – 0.2 \text{ rad/s}}{16 \text{ s}} = \frac{0.8}{16} = 0.05 \text{ rad/s}^2$