Peoples Physics Book Version-3

http://www.ck12.org Chapter 6. Centripetal Forces

For any object a heighthabove the surface of the earth, the force of gravity may be expressed as:

F~G=Gmearthmob j

(rearth+h)^2

Now we make the approximation that

rearth+h≈rearth

then, we can rewrite the above as

F~G=Gmearth

r^2 earth

︸ ︷︷ ︸

gearth~

×mob j=mob j×~g Gravity on Earth

We can do this because the quantity in braces only has constants; we can combine them and call their productg.
Remember, this is an approximation that holdsonlywhen objects are near (think in our atmosphere) the surface of
Earth.

We call the quantitymgan object’sweight. Weight is different from mass — which is identical everywhere — since
it depends on the gravitational force an object experiences. In fact, weight is the magnitude of that force. To find the
weight of an object on another planet, star, or moon, use the appropriate values in the Law of Gravity formula and
solve forFG

Key Applications

• To find the maximum speed that a car can take a corner on a flat road without skidding out, set the force of
  friction equal to the centripetal force.