Can gravitational influence be measured?

[AstrophysicsX]

All objects exert a gravitational force relative to its size. The sun keeps Earth and the other planets in orbit this way. Is there any way to measure how much of this force objects give off?

 

[mathman]

I don't know what you mean by "give off". Weight is the measure of gravitational force.

 

[HallsofIvy]

As mathman said, the weight of an object (say, on the earth) is the measure of the gravitational force of the Earth on the object and so, because the situation is symmetrical, also the gravitational force of the object on the earth.

Similarly, we can measure the "weight" of a planet by information about the orbit.

 

[D H]

You can't measure weight, not directly at least. Scales, depending on type, measure either mass or apparent weight (everything but gravity). Accelerometers measure acceleration due to everything but gravity.

 

[espen180]

Accelerometers measure acceleration due to everything but gravity.

In free fall, you mean? If an accelerometer was lying on the Earth's surface, it would measure the gravitational acceleration of the Earth, right? (Though I guess this can be interpreted as the acceleration of the refrence frame, rather than Earth's gravity.)

 

[D H]

In free fall, you mean? If an accelerometer was lying on the Earth's surface, it would measure the gravitational acceleration of the Earth, right? (Though I guess this can be interpreted as the acceleration of the refrence frame, rather than Earth's gravity.)

No. An accelerometer lying on the Earth's surface registers an acceleration of about 1g pointing upward. Here are two perspectives on how accelerometers work.

Newtonian point of view: An accelerometer measures the acceleration of the accelerometer due to the net real, non-gravitational force acting on the accelerometer. An accelerometer does not measure pseudo forces such as centrifugal force, Coriolis effect, etc.: Those aren't real forces.

General relativistic POV: An accelerometer measures the acceleration of the accelerometer due to the net real force acting on the accelerometer. Gravitation is a pseudo force in general relativity, and accelerometers do not measure pseudo forces.

 

[espen180]

Okay, I understand. Thanks for the explanation.