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Friction coefficient

Last week, using a sled and some kg masses, I plotted a graph of total mass of the sled against the force required to move the sled, and draw a line of best fit. In order to get the coefficient of friction of the surface, I draw the line of best fit on excel, and found its equation, using y= mx + c, to find the gradient. Is this gradient the coefficient of friction?

If applying this to the scene of a car accident, how would I find the work done against friction by the car when it brakes, if given the mass of the car and the length of tyre marks on the road, using the previously calculated coefficient?

Reply 1

Phaedos

Well frictional force f=k*mg (where m is mass, g is accel due to grav, k is coeff). . If we assume that you measured the force at the very point the mass was about to move then force applied=k*g*m....so if you're plotting f against mass m, then it should in an ideal world be a straight line that passes through the origin, and with gradient eqaul to k*g