Phys 212 F07 Spring 2015
Simply put a force is a push or a pull. A force is an
action the causes some kind of reaction from another object.
Force is also a vector; it has both a direction and
magnitude. Forces also require and agent, a cause of the
force. There are two types of forces. A contact force, a
force that depends on the agent touching the object or not
and a long-range force, a force tat acts on an object
without any physical contact, such as gravity.
image from:
http://physics.tutorvista.com/forces.html
Friction is an agent of
force. A frictional force is a force exerted by a
surface and is always tangent to the surface. There
are two kinds of friction, kinetic friction and static
friction. Kinetic friction happens when an object
slides across a surface and it opposes the motion,
meaning that the friction force vector will point in
the opposite direction as the velocity vector. Static
friction is the force that keeps objects stationary on
a surface, it prevents motion. The static friction
vector will point in the direction that is necessary
to prevent motion.
image from:
http://www.school-for-champions.com/science/friction.htm#.VTXj9zvF8i4