1. The problem statement, all variables and given/known data A skateboarder + skateboard has a combined mass of 70 kg. How much force is required to prevent them from rolling down a 15 degree incline? 2. Relevant equations Weight = 70kg * 9.81m/s^2 Normal = cos 15 * W Friction = sin 15 * W 3. The attempt at a solution I solved for friction but my instructor says that I should solve for the Normal force because that is the largest force that must be overcome to get the mass rolling. I do not understand why exactly since the Normal force isn't a force acting in same direction as the rolling direction. My instructor said that this isn't just a mass sliding down but that the mass is on wheels so once the Normal force is overcome, the skater will start rolling down. Am I just mixing up/missing some basic concept?