Is gravity on earth greater or less then gravity on Venus?

Answer 1

The gravity present on a planet is usually denoted by the acceleration an object would experience due to gravity on that planet's surface. If we stick to Newtonian gravity (which should be adequate for our present purpose) the acceleration due to gravity on a planet is given by:

a = G*M / R^2

Where G is Newton's gravitational constant, M is the mass of the planet, and R is its radius (remember we are standing on the surface).

(Note: Here I have neglected the vector qualities of acceleration, this will not matter at present, the acceleration will be pointing down, towards the center of the planet.)

From this formula we can see that the acceleration increases if the mass of the planet increases. This is to be expected; gravity (in Newtonian gravity) is caused by mass, and thus a bigger mass means a stronger gravitational field. Since Venus is less massive than Earth we might expect the surface gravity on Venus to be less than on Earth.

However, we also have the R^2 in the denominator. This means the surface gravity on a planet will increase if the radius decreases (and the mass stays the same). This is also clear; if the radius is less then you stand deeper into the gravitational field. Venus is about the same size as Earth so this effect should not play as much a role as the difference in mass does.

Thus, just by using these arguments we can already conclude that the surface gravity on Earth is larger than the surface gravity on Venus.

Let us now look at some numbers. Earth's surface gravity is about 9.81 m/s^2 (it varies slightly from location to location). And Venus' surface gravity is 8.87 m/s^2, which is less, as expected.

This means that if you weigh 70 kg on Earth you will weigh 70*(8.87/9.81) = ~63 kg on Venus.

Answer 2

Gravity on a planet is directly related to its mass. Venus is very close in mass to earth with about 10% less mass. Therefore, Venus' gravity is about 90% that of earth.