Why is the distance that two objects are apart (r) when it should be half of it?

[slain4ever]

Homework Statement

what is the gravitational force of atraction between
two oranges of 0.12kg each placed 0.2m apart

Homework Equations

F=(Gm1m2)/r^2

The Attempt at a Solution

it works when i put r = 0.2 but shouldn't it be 0.1 (half the diameter is the radius isn't it?)

 

[Matterwave]

Your intuition for F is correct for things like the Earth, where we are a distance r=radius from the Earth's center. But, more generally, r just represents the distance between the two objects. In this case, the distance is just .2m.

 

[thebigstar25]

what i know about r in these kinds of questions that it is the distance from the centre of object1 to the centre of object2, so if that 0.2 represents:

radius of object1+raduis of object2+the distance between the two surfaces , then your work is done .. but becareful with other questions this one i assume that they meant that 0.2 is the distance from centre object1 to centre object2 ..