   Motion on a slope
  Hi,I really don't have a lot of experience with physics I was hoping someone might be able to help me out.I'm trying to understand how elementary physics of sliding down a slope.From what I've read, this is what I understand:On a slope gravity has 2 components, a perpendicular component (acting on the y axis, Fy) and a component that is parallel to the slope (acting on the x axis, Fx). Fx = mass * accel. due to gravity * sine(angle of slope)Fy = mass * accel. due to gravity * cosine(angle of slope)The normal force is cancelled out by the perpendicular component of gravity, so it's possible to say that the Friction on the slope, Ff, is mu * Fy.And if I want to calculate the angle of the slope I can use the dot product (with some manipulation) of the object's positional vector and the vector of the bottom of the slope. What I'm stuck on is how to get from these forces to the velocity that an object might move down the slope at.I'm guessing Newton's 2nd law, F = ma, is used but I'm not sure how.I guess I may be able to sum the forces acting in the x-direction, subtract them from the friction, and divide by mass to get the acceleration at least. I'm really not sure and would be really grateful for any help that anyone can give me.Thank you,Max :)   
  Max, you're on the right track! So, to get from acceleration to velocity, you have to do a little calculus. Velocity is the time integral of acceleration. And, from there, position is the time integral of velocity. If the slope is fixed, and friction is fixed, then the force in the x direction will be constant and the equations for motion in the x axis will end up looking just like the equations for an object dropping in open air, but with the force being adjusted by kinetic friction. Velocity in the y direction is fixed at zero, of course, for the simplest case.One complication is if the object is starting from rest, the static friction is greater than when the object is moving...if the x component of the weight does not exceed static friction, the object will never start sliding. But if it does, then the friction will switch over to the lower kinetic friction.Now...a round object rolling down the incline, that is another complication. The info about is about linear sliding without rolling or tumbling.   ;  Thanks for the reply Graham :)I'll spend some time looking into the next part (the velocities) tonight, hopefully i'll be able to figure it out without too much hassle.   