Physics Lesson 7.2.5 - Angular Momentum

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Welcome to our Physics lesson on Angular Momentum, this is the fifth lesson of our suite of physics lessons covering the topic of Dynamics of Rotational Motion, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

Angular Momentum

Angular momentum, L, is a vector quantity (more precisely, a pseudo-vector) that represents the product of a body's rotational inertia and rotational velocity (in radians/sec) about a particular axis. It is the equivalent of momentum in linear motion.

Mathematically, we can write

L = I × ω

The unit of angular momentum is [kg × m2 / s].

Example 4

What is the angular momentum of Earth when revolving around itself? Take the following approximate values: MEarth = 6 × 1024 kg, REarth = 6400 km and TEarth = 86400 s.

Solution 4

Earth can be considered as a solid sphere. Therefore, its moment if inertia is

I = 2/5 m × R2

We have, R = 6400 km = 6 400 000 m = 6.4 × 106 m. Also, m in the formula is replaced by M as Earth has a very large mass. Hence, we can write:

I = 2/5 M × R2
= 2/5 × 6 × 1024 × (6.4 × 106)2
= 1.64 × 1037 kg × m2

Now, let's calculate the angular velocity of Earth. Since for one revolution φ = 2π and t = T, we have

ω = φ/t
= /T
= 2 × 3.14 rad/86400 s
= 7.27 × 10-5 rad/s

Hence, Earth's angular momentum is

L = I × ω
= 1.64 × 1037 kg × m2 × 7.27 × 10-5 rad/s
= 1.19 × 1033 kg × m2/s

You have reached the end of Physics lesson 7.2.5 Angular Momentum. There are 8 lessons in this physics tutorial covering Dynamics of Rotational Motion, you can access all the lessons from this tutorial below.

More Dynamics of Rotational Motion Lessons and Learning Resources

Rotation Learning Material
Tutorial IDPhysics Tutorial TitleTutorialVideo
7.2Dynamics of Rotational Motion
Lesson IDPhysics Lesson TitleLessonVideo
7.2.1Moment of Force as Analogue of Force in Translational World
7.2.2Moment of Inertia
7.2.3Moment of Inertia in Different Systems of Rotational Motion
7.2.4Newton's Second Law for Rotational Motion
7.2.5Angular Momentum
7.2.6Work in Rotational Motion
7.2.7Kinetic Energy in Rotational Motion
7.2.8Power in Rotational Motion

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  2. Rotation Physics tutorial: Dynamics of Rotational Motion. Read the Dynamics of Rotational Motion physics tutorial and build your physics knowledge of Rotation
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  6. Continuing learning rotation - read our next physics tutorial: Centripetal Force

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