Understanding Moon's Lack of Gravity: The Science Behind It

  • Context: Undergrad 
  • Thread starter Thread starter jtesttubes
  • Start date Start date
  • Tags Tags
    Gravity Moon
Click For Summary

Discussion Overview

The discussion centers around the nature of gravity on the Moon compared to Earth, addressing misconceptions about the Moon's gravitational force and exploring the scientific principles behind gravitational strength, mass, and density. The scope includes conceptual clarifications and technical explanations related to gravitational physics.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that the Moon does have gravity, evidenced by the behavior of objects like the Apollo astronauts and experiments such as the hammer and feather drop.
  • Others question the initial premise of zero gravity on the Moon, emphasizing that the Moon's gravitational force is weaker than Earth's due to its smaller mass.
  • It is noted that gravitational force depends on both mass and distance from the center of the celestial body, with density also playing a role in determining gravitational strength.
  • Some participants discuss the relationship between gravitational potential energy and gravitational field strength, clarifying that while the Moon's gravitational potential energy is less than Earth's, it still possesses gravity.
  • There are references to the formulae governing gravitational force and potential, with some participants suggesting that these mathematical expressions provide clearer insights than verbal explanations.

Areas of Agreement / Disagreement

Participants generally agree that the Moon has gravity, but there is disagreement regarding the implications of its weaker gravitational force compared to Earth. The discussion remains unresolved on the nuances of gravitational potential energy versus gravitational field strength.

Contextual Notes

Some statements rely on assumptions about definitions of gravity and gravitational potential energy, which may not be universally agreed upon. The discussion also reflects varying levels of understanding regarding the mathematical relationships involved.

jtesttubes
Messages
16
Reaction score
0
What are the properties constitute to have zero gravity in moon. Why Earth has gravitational force while moon does not have? I need a concrete scientific explanation.
 
Physics news on Phys.org
The moon does have gravity. Notice the pics of the Apollo astronauts walking about. Haven't you seen the video of the dropped hammer and feather experiment?
 
jtesttubes said:
What are the properties constitute to have zero gravity in moon. Why Earth has gravitational force while moon does not have? I need a concrete scientific explanation.

The moon does exert a force on other objects that have mass. In the parlance of our times, it does have gravity. Now the moon does not have an atmosphere... is that what you meant?
 
http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html"
 
Last edited by a moderator:
jtesttubes said:
What are the properties constitute to have zero gravity in moon. Why Earth has gravitational force while moon does not have? I need a concrete scientific explanation.
The moon's gravitational force is weaker than the Earth's because gravitational force is directly proportional to mass, and the moon's mass is smaller than the earth's.
 
Don't forget that g actually depends on distance from the centre of the planet (radius) and the density.
 
anything with mass has gravity
 
sophiecentaur said:
Don't forget that g actually depends on distance from the centre of the planet (radius) and the density.

density?
 
Well, it depends on the mass and that is the product of volume (which depends on radius) and the density.
 
  • #10
Anonymous217 said:
density?
Yes, density determines where the surface of the mass is and the resultant gravity. If we create a new planet with higher density than the Earth with the same mass but with the size of the Moon, this object would have higher gravitational pull on its surface than both the current Moon and Earth. Because you're close to the centre.
 
  • #11
This is one of the many examples in Science where the actual FORMULA says it all and much better than words.
 
  • #12
jtesttubes said:
What are the properties constitute to have zero gravity in moon. Why Earth has gravitational force while moon does not have? I need a concrete scientific explanation.

You have been wildly misinformed sir. The moon has gravity, about 1/6 the gravity that Earth has. Any thing with mass (everything really) has gravity. Even light has it's own gravity (since light is a form of energy and the mass off energy is equal to energy/the speed of light^2).
 
  • #13
the moon does have gravity however its gravitational potential energy is much less than that on earth, due to the mass difference, since the moon has less mass than Earth its gravitational pull is much weaker. Earth's GPE is roughly 9.8 Moons GPE is i think around 1.6~1.8
 
  • #14
doc.madani said:
the moon does have gravity however its gravitational potential energy is much less than that on earth, due to the mass difference, since the moon has less mass than Earth its gravitational pull is much weaker. Earth's GPE is roughly 9.8 Moons GPE is i think around 1.6~1.8
Don't confuse gravitational potential energy with the strength of the gravitational field at the surface. The strength of the Earth's gravitational field is about 9.8 N/kg (or m/s^2) at its surface, while the moon's is about 1.6 N/kg at its surface.
 
Last edited:
  • #15
Potential is -GM/r.
Field (g) is GM/r2.

M= 4pi r3 d/3
(where d is density)
So
g = 4pi G d r3/3r2
which means g = 4pi G d r/3
and the potential is -4pi G d r2/3

That says it all, doesn't it?
 

Similar threads

Extinction event in my story, is it believable?
  • · Replies 30 ·
2
Replies
30
Views
5K
Undergrad Gravity on the Moon vs. on the spinning Earth
  • · Replies 10 ·
Replies
10
Views
2K
High School The Sun's Influence on the Moon's Orbit: Is it Negligible?
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad The gravitational center of the Earth
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Where does the energy for gravity come from?
  • · Replies 32 ·
2
Replies
32
Views
9K
Undergrad How Do Moons Influence the James Webb Telescope's Position at Lagrange Point L2?
  • · Replies 4 ·
Replies
4
Views
2K
Interplanetary Portals vs Gravity
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Understanding the Discrepancy: Why Does the Moon Have Less Gravity Than Earth?
  • · Replies 8 ·
Replies
8
Views
2K
Questions about a habitable second moon
  • · Replies 37 ·
2
Replies
37
Views
8K
Undergrad Does Organic Matter Experience Gravity on the Moon?
  • · Replies 15 ·
Replies
15
Views
2K