Describe 3 ways gravity works with water to in the erosion process

1. gravity keeps the water moving downward or just in general
2. the water has to  move across the surface for so long till eventually it just erodes away.
 those are the only two i know sorry.

Gravity causes erosin by pulling drit,rocks and soil downward 

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference.