Designing a roller coaster requires careful consideration of several physics concepts. Most notably, mechanical energy must be kept track of to ensure the Roller Coaster completes the course.
Friction is also an important consideration, however it is rather complicated to deal with exactly.
A simple but poor approximation can be made by assuming a constant drag force resulting in a constant energy dissipation per unit track length. This is not very accurate as shall be seen later, but it is better than ignoring friction all together. Another important design consideration is the accelerations experienced by the passengers. The goal here is to maximze the excitement of the ride without actually endangering the passengers. By comparison, people can withstand accelerations on the order of 10 g in directions perpendicular to their bodies without any permanent adverse effects, however most Roller Coaster cars would jump their tracks at such extreme accelerations.