a force exerted between two surfaces sliding against each other (must be moving)
a force exerted between two surfaces trying to slide against each other (but not yet moving)
a fluid used to reduce friction by creating a thin layer between the microscopic "hills and valleys of a surface"
small rotating spheres that reduce friction by changing sliding motion into rolling motion
the measure of how much twisting force causes an object to rotate
the perpendicular distance from the axis of rotation to the line of action of the force. it is a factor used in calculating torque.
line of action
an imaginary line in the direction of a force and passing through the point where the force is applied
axis of rotation
a point around which an object rotates
a condition that occurs when all the torques applied to an object add to zero (balanced torques)
a measure of how resistive an object is to rotation. it depends on the objects mass and how the mass is distributed. its symbol is "I"