Different kinds of Friction No Friction Static Friction Sliding Friction Rolling Friction
Weight of
Ideal Force
Force Needed Force Needed to Force Needed to
Needed to Push
Object
to Start Moving Keep Moving Keep Rolling
Up Ramp
480N
160 N
192 N
178 N
166 N
900 N
300 N
360 N
333 N
310 N
750 N 250 N
300 N
278 N
Copyright Glencoe/McGw-Hill, a division of The McGraw-Hill Companie
259 N
3. A ramp is 3 meters long and 1 meter high. Under ideal conditions, this ramp would reduce the
force needed to raise an object by a factor of three. However, friction is a force that opposes
motion between two surfaces that are touching. According to the chart, which kind of friction
opposes motion with the greatest force?
a. No friction
b. Static friction
c. Sliding friction
d. Rolling friction

People with normal vision cannot focus their eyes underwater if they aren't wearing a face mask or goggles and there is water in contact with their eyes. in a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. with the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 2.05cm in front of the eye.)