# Orbital vs. Angular speed

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1. Jan 11, 2017

### alybtd

Is there a difference between orbital speed and angular speed when an object or star is considered to be in a circular motion around another?

2. Jan 11, 2017

### Electron Spin

Welcome, might want to post your Q in the proper area.. Welcome anyway..

3. Jan 11, 2017

### alybtd

Thanks!

4. Jan 11, 2017

### Electron Spin

Depends if its a homework question or a general question. Respectively, homework or astronomy sections would work.

I would do a search here. I am sure this question has been asked about 3 million times!

Electron Spin

5. Jan 11, 2017

### Drakkith

Staff Emeritus
Welcome to PF!

I've moved the thread to the General Physics forum.

6. Jan 11, 2017

### alybtd

Thank you! I kinda found a way to figure it out and I found the right answer to what I was looking for, so yeah thanks!

7. Jan 11, 2017

### alybtd

Thank you!

8. Jan 11, 2017

### Cutter Ketch

- Orbital speed means the speed transverse to the orbit. It is speed in the normal usage: distance travelled per unit time. It has units like m/s. For a circular orbit it is the circumference over the orbital period.
- angular speed differs in that it is the angle travelled per unit time. It has units like rad/s. For a circular orbit it is 2 π / the orbital period. Note: Since it is "transverse to the orbit" the direction at any point in time is well defined and this is often called orbital velocity.

The two are related by the radius of the orbit. For a circular orbit of radius r
Orbital speed = r * angular speed.

Caveat: if you are hearing both these phrases be careful that the speaker is using them both in reference to the same rotational motion. They might be using one in reference to the orbit and the other in reference to the spin or something like that.