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Topic: Determining accleration due to gravity (Read 11 times) previous topic - next topic

michinyon

"I do understand the units' equivalency, and indeed have understood this stuff since  about 1971.... I doubt if I'd have graduated as a civil engineer without having understood the relationship between force, mass and acceleration.."

You might have,  if you were an American.   The distinction between force, mass and weight becomes rather obfuscated in their system.

michinyon

OK, so suppose I am not interested in measuring small fluctuations in the force of gravity,  because I am not looking for buried iron ore deposits or big meteors.

Suppose I want to measure the direction of the graviational force,   and I want to do this from a moving platform like a car or an aircraft.

If I get a 3D MEMS accelerometer,  that will do a good job if the vehicle is stationary or moving at a constant velocity,   but otherwise,  it won't.

Is there another way to measure the direction of the gravitational force which will work in an erratically moving vehicle ?

liudr


OK, so suppose I am not interested in measuring small fluctuations in the force of gravity,  because I am not looking for buried iron ore deposits or big meteors.

Suppose I want to measure the direction of the graviational force,   and I want to do this from a moving platform like a car or an aircraft.

If I get a 3D MEMS accelerometer,  that will do a good job if the vehicle is stationary or moving at a constant velocity,   but otherwise,  it won't.

Is there another way to measure the direction of the gravitational force which will work in an erratically moving vehicle ?

Thanks to Einstein's general relativity, you can't tell between gravity and acceleration. You can't find gravity with accelerometer if you yourself is accelerating. If you have a gyroscope, you can spin it in the direction of gravity and see how your down direction compares with it, I suppose.

wwbrown

How about a magnetometer if you only want to measure the direction of the acceleration due to gravity.  I am pretty sure that a magnetometer will not be affected by linear or rotational acceleration.

liudr


How about a magnetometer if you only want to measure the direction of the acceleration due to gravity.  I am pretty sure that a magnetometer will not be affected by linear or rotational acceleration.


Is that a magnetic sensor? It can only measure your angle to local magnetic field, not your angle to local gravity. Facing north while tilting up 30 degrees and facing south while tilting down 30 degrees will read the same on a magnetic sensor.

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