Which of these statements describe friction? check all that apply. 1 friction allows objects to slide over each other without any resistance. 2 friction resists motion. friction is a force that acts from a distance. 3 friction is a contact force. 4 friction is caused by microscopic bumps and ridges on surfaces.

Answers:

3 Friction is a contact force.  

4 Friction is caused by microscopic bumps and ridges on surfaces.

Explanation:

Friction is a force that opposes the motion of an object. For example, when you are sliding a box along a surface, there is a friction force that resists the motion.

The friction force is caused by the contact between the molecules of the external surfaces of the object and the molecules of the surface where the object is sliding over. Therefore, it is a contact force (statement 3) and also it is caused by the bumps and ridges on the surfaces (statement 4): in fact, if the surfaces were perfecly smooth, in theory there would be no friction (but this is impossible in reality).

the tires are rotating at 0.434 rpmlinear speed=45 m/sdiameter=0.550 mradius=0.275 mnow v= rωω= v/rω=45/0.275ω=163.6 rad/sω=163.6 rad/s (1rev/2π rad) (60s/1m)ω=1563 rpm