What is the word for the momentum of the Earth orbiting the Sun?

[sevensages]

I would like to explain to someone about why the Sun's gravity does not pull the Earth into the Sun. I know that the reason that the Sun's gravity does not pull the Earth into the Sun is that the momentum of the Earth orbiting the Sun is in equilibrium with the Sun's gravity.

What I need to know is what is the correct word for the type of momentum in which the Earth orbit's the Sun. So the purpose of this thread is to figure out what the correct word is.

I looked up angular momentum in Merriam-Webster's online dictionary, and I am still confused.

Merriam Webster's online definition of angular momentum is below:

Angular Momentum: A vector quantity that is the measure of the rotational momentum or a rotating body or system, that is equal in classical physics to the product of the angular velocity of the body or system and its moment of inertia with respect to the rotation axis, and that is directed along the rotation axis.

So Merriam webster's dictionary basically defines angular momentum as a measure of rotational momentum. It's my understanding that the rotational momentum of the Earth is the Earth's spinning 360 degrees once every 24 hours, not the Earth's revolving around the Sun once every 365 years. So I am not sure if angular momentum is the correct word here.

What is the correct word for the momentum of the Earth's orbiting the Sun once every 365 days?

 

[Baluncore]

What is the correct word for the momentum of the Earth's orbiting the Sun once every 365 days?

Orbital angular momentum.

 

[sevensages]

Orbital angular momentum.

Ok thank you

 

[Filip Larsen]

When explaining this to your friend it may also be relevant (as you may already know) to mention that in the context of the two-body problem then

1. the orbital angular momentum vector is conserved (i.e. unchanged) in both direction and magnitude,
2. the unchanged direction relates directly to the orbit being planar, that is, having a fixed orbital plane, and
3. the unchanged magnitude relates direct to Kepler's second law of planetary motion, i.e. that the body sweeps out equal area in equal time.

Note that when modelling orbits of multiple massive bodies like the planets of the solar system, the statements above are also approximately true over time to the extend that the bodies do not pass near each other, that is, the orbital angular momentum (and several other key orbital parameters) for planets in a stable solar system will tend to oscillate around a fixed value, which is utilized in the concept of using osculating orbits to model how planetary orbits change over time.