What is Surface Gravity?

[Mitchell]

In a Moon/Earth Comparison Data sheet I received from NASA, they list the surface gravity at 9.80 m/s2. They also list surface acceleration at 9.78 m/s2. What is surface acceleration? All the problems relating to gravity in my Physics text (so far) calls Earth's gravity constant as 9.80 m/s2.

[Sirus]

Surface gravity is the acceleration due to gravity at the surface of a body (this is used for physics problems that happen close to the ground). I would think surface acceleration is the same thing, but I'm not sure why NASA lists it as 9.78.

[Bartholomew]

Maybe they are factoring in the rotation of the earth.

[Chi Meson]

THis is due to the effect mentioned in that other thread! (k12 zone) THe "surface gravity" is the actual gravitational field strength "g" at the surface of the earth. The unit of this field strength should properly be N/kg, but this unit is equivalent to m/s^2.

The actual "free-fall" acceleration will be less than "g" because due to the rotation of the earth, some of the gravitaitonal force is required for centripetal acceleration (to keep us going in a circle with the earth's surface). This surface accelration changes depending on where you are in the world. It is least near the equator, where "g" will be reduced by 0.033 m/s^2.

[Bartholomew]

The information and explanation are on these two pages:

http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
http://nssdc.gsfc.nasa.gov/planetary/factsheet/fact_notes.html

(Yes, the reason for the difference is rotation of the earth)

[Sirus]

That should satisfy Mitchell. :smile:

[Mitchell]

It sure does and thank you to everyone.