Why can't I go as Fast as I want?
Or, The effect of Friction
So if gravity is constantly pulling you down the hill, then why dont you keep going faster? Friction the bane and cause of movement. Friction is the another force that acts on you while sledding, it yends to slow you down. But without friction there would have been no way for you to get started, or even make it up the hill. There are two types of friction, Static friction and Kinetic friction. While moving kinetic friction is relavant so that is the one I will talk about.
As you are being pulled down the hill by gravity, you may think that you would keep accelerating at a constant speed, all the way down the hill. This is not that case, Kinetic Friction acts as a negative force to the direction you are traveling. So by traveling down the hill the contact made from the sled and snow or ice creates a frictional force directed back up the hill. Slowly decreasing your rate of acceleration, it doesnt stop you, because while traveling down the hill the acceleration due to gravity is great enough to be counteracted by the pull of gravity.
The material the sled is made of also determines how much friction there will be against you. Every substance has its own coefficient of kinetic friction. The greater the coefficient the greater the negative acceleration will be done by friction. 1.0 being the greatest amount of friction, and 0.0 being the least. Here is a table of some coefficients that may be usefull while sledding:
| Substances | Coefficients of Kinetic Friction |
| Plastic Sled on Snow | 0.3 |
| Waxed wood on wet snow | 0.1 |
| Waxed wood on dry Snow | 0.04 |
| Steel Sled on Snow | 0.03 |
According to the coefficients of kinetic friction in the above table, Calvin and Hobbes have the right idea by using the wooden tobaggan. It has one of the lowest coefficients of friction, resulting in a very low negative acceleration, and an overall high top speed all the way down the hill.