EDUCATION SYSTEM IN TANZANIA: Experimental facts about friction

Sunday, October 26, 2014

1.: f_s $\le$ $\mu_{s}^{}$ N where $\mu_{s}^{}$ is the coefficient of static friction and N is the magnitude of the normal force. Equality holds when the object is on the point of slipping: f_s(max) = $\mu_{s}^{}$ N .
2.: f_k = $\mu_{k}^{}$ N where $\mu_{k}^{}$ is the coefficient of kinetic friction and is approximately constant for any given pair of materials.
3.: Values of $\mu_{s}^{}$ and $\mu_{k}^{}$ depend on the nature of the surfaces that are in contact. Usually $\mu_{k}^{}$ < $\mu_{s}^{}$ . Examples: rubber on concrete $\mu_{s}^{}$ = 1.0, $\mu_{k}^{}$ = 0.8 ; waxed wood on wet snow $\mu_{s}^{}$ = 0.14, $\mu_{k}^{}$ = 0.10.
4.: The direction of the force of friction is opposite to the direction the object wants to move.
5.: $\mu_{k}^{}$ and $\mu_{s}^{}$ are nearly independent of the area of contact between the two surfaces.
6.: $\mu_{k}^{}$ is nearly independent of the velocity of the object under consideration.

EDUCATION SYSTEM IN TANZANIA