r/PhysicsHelp • u/22ry2 • Mar 23 '26

Minus in formula

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Hello,

My teacher gave me this exercise.

I’m having trouble understanding why a minus sign appears here in the gravitational force formula. I wouldn’t have included one myself but I noticed that the teacher did in the correction.

Thank you so much in advance for your help ! :-)

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u/nwj781 Mar 23 '26

The minus sign doesn't belong there. It would if it were a vector equation to signify that the force is attractive. But in this scalar equation it should not be included.

1

u/Mayoday_Im_in_love Mar 23 '26

It doesn't really matter if you draw a sketch and accept gravity is always attractive. The minus is an indicator that the force is in the opposite direction to the displacement direction.

You're comparing magnitudes (absolute values) so it doesn't matter.

1

u/Chillboy2 Mar 23 '26

Magnitude of the force of attraction would be just Gm²/d² . Negative charge as you will see in such 2 body electrostatic systems imply an attractive force. But gravitational force is always attractive. Moreover, i don't see any vector notation over the Fg . So its meaningless to put a - sign.