Sierra Pine
1/11/14
2A
What is Friction?
Friction is the resistance that one surface or object encounters when moving over another.
No matter which direction something moves in, friction pulls it the other way. Without it we
would be sliding and falling all over the place. Friction could not exist without the presence of
gravity, pulling the objects down. In order to calculate the amount of friction you need an
equation; Fᵣ=Mw. Fᵣ represents the resistive force of friction. M is the coefficient of friction for
the two surfaces; the mass of the objects. W represents the normal or perpendicular force pushing
the two objects together, in other words, W is gravity or weight.
There are two types of friction: static friction and kinetic friction. Static friction deals
with motion whereas kinetic friction does not. It is that threshold of motion which is
characterized by the coefficient of static friction. Static friction describes the force needed to
initially move a stationary object. The coefficient of static friction is typically larger than the
coefficient of kinetic friction. Kinetic friction (sliding friction) describes the force needed to keep
an object moving along a surface. In simpler terms, static force is the beginning force to get it
going and kinetic force keeps it going.
Friction is helpful when trying to stop whether we are walking or in a car. Without it we
would have a very hard time stopping (imagine us on ice all the time). It’s also helpful when
trying to get an airplane to fly. The friction of air on the wing causes the plane to stay airborne.
Friction can be harmful when trying to travel. Our cars would get much better gas
mileage without air and tire friction and save money one gas. Another example of harmful
friction is when you fall on the ground and hurt yourself. Without friction, when we fall we
would just slide and be able to avoid skinned knees.