# Gravitational field intensity

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What's the difference between the formula of $g = \frac{F_g}{m}$ and $abs(g) = G\frac{m}{r^2}$?

Note: abs(g) means absolute value. I don't know the latex code to input absolute.

Because the question asked me: Calculate the gravitational field intensity 340 km above the planet Venus.

I used the second formula above, where r = 340,000 m; G = 6.67 x 10^-11; m = 4.83 x 10^24 kg. I got $2786.859862 \frac{N}{kg}$ for the answer. Is this correct?

I still don't know why I used the second formula, not the first one, though?

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They're the same thing.

$\mathbf{g}=\frac{\mathbf{F}}{m}$

The force is just

$G\frac{mM}{r^2}\hat{\mathbf{r}}$

To get the absolute value just whack | around the things your taking abs of, there should just be a key on your keyboard for it.

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All right thanks.

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Because the question asked me: Calculate the gravitational field intensity 340 km above the planet Venus.

I used the second formula above' date=' where r = 340,000 m; [/quote']

Just a query, but r is the distance from the centre of the mass NOT the surface... so is that what they mean by "above the planet"???

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Just a query, but r is the distance from the centre of the mass NOT the surface... so is that what they mean by "above the planet"???

Yup, I just noticed that in my textbook. I have to find the distance that runs toward the Venus's centre, and add it to the distance "above the surface".

Thanks.

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