The Beginning: Downhill
It's a safe bet that as you begin
you flight down the hill your not thinking to yourself, "I wonder what
is actually happening to me as I sled down this hill." But what does
go on when you are moving down the hill? The
simple answer is gravity
Gravity
and normal forces are the first two basic forces
acting upon you. Gravity pushes against you towards the hill, while the normal
forces act in the opposite direction. With these two forces acting in opposition
of each other, they would appear to cancel each other out, but then why do
you still move down hill? The answer lays in the hill itself. It is because
of the sloped surface of the hill that you move. In a perfectly horizontal
hill, your net force would be zero, and on a perfectly vertical hill you would
have a net force equal to your weight.
The diagram to the left shows the resulting forces
and how gravity pulls you down the hill. Since the vertical forces of gravity
are canceled by the normal force. There is still the horizontal effect of
gravity's pull. Giving you a force which is equal to your mass times the acceleration
due to gravity times the sine of the angle of the hill.
If you keep increasing speed as you go down the hill then why do you slow down once you reach the bottom? Since you are no longer going down an incline the normal forces and forces of gravity cancel each other out. Your velocity will be the same as when you left the bottom of the hill due to inertia. The only reason you slow down is becuase of wind resistance, which we have ignored for simplicity sake, and friction which will be explained inthe next section.