Comment by antod
2 days ago
My physics is very rusty and very basic, but I don't think classical physics said gravity was a force either. eg in Newton's 2nd law or engineering mechanics, gravity is the "a" or the "g" not the "F".
2 days ago
My physics is very rusty and very basic, but I don't think classical physics said gravity was a force either. eg in Newton's 2nd law or engineering mechanics, gravity is the "a" or the "g" not the "F".
Well congratulations, you just stated the equivalence principle that led Einstein to GR (you need special relativity and a bit of maths and you’re there)!
:) I see your confusion. But the F is caused by gravity there. The special case you are refering to (I think you are thinking about the Weight = g * mass of body) comes from a more universal expression.
If you look at the proper expression that calculates it's force, it becomes clear:
F = G * m1 * m2/ r^2 (so, gravity is the force between masses).
P.S. G is the universal constant of Gravity here, not the gravity itself.
Yup, knew that equation. My point was I only ever recalled the effects of gravity on mass being called a force, and never gravity itself being called a force. eg no mass, no force - gravity being a field that causes forces (on mass) rather than the force itself.
That distant memory came from engineering school, where it was classical mechanics all the way down. The only non classical stuff was just a tiny amount in a first year physics paper.
Then again, maybe the way classical physics got taught was a bit different after Einstein so as not to directly contradict relativity. Eg maybe before relativity it really was described as a force?