Friction, Weight, Gravity

Despite the physics which requires that light and heavy objects travel down an inclined plane at the same rate, I have trouble reconciling this with my own experience skiing or biking down hills. I invariably reach the bottom of the hill before my teen-age daughter. My larger size should actually slow me down due to increased wind resistance and my greater weight should produce more friction while skiing, again slowing me down. The difference in friction coefficients of the skis and the moments of inertia of the bikes should be negligible.
- Pierre L'Heureux (age 60)
Glastonbury, CT USA

You're right that the air friction and ski friction should be bigger on you than on your daughter.  However, in calculating the effect of those fores on acceleration, you have to divide by mass. For objects of the same shape and sped, the air friction does not fully double when the volume and mass double. So that frictional effect on the acceleration decreases as the mass increases.

Mike W.

(published on 08/22/2010)