Frictional and Movable Forces
Why does Force include come in frictional force and a movable force?
What is the difference between the two forces?
Why is the formula for force F=ma??
I am not sure I follow your first question, but I think it might have
with the difference in static friction and kinetic friction (static meaning
"at rest", and kinetic meaning "moving"). Let's take for instance a wooden
box sitting still on a level concrete floor. The force required to start
the box moving is the force required to overcome the friction between the
floor and the box. It turns out the formula for that is (static friction *
weight of the box) = force required to get the box moving. Now, once the
box is moving, the only thing resisting the force pushing the box is the
kinematics frictional force, which is less than the static frictional force.
Once again the formula is (kinetic friction*weight of the box)= force
required to keep the box moving. Static friction is always greater than
kinetic friction, so the force required to get something moving is always
greater than that required to keep it moving.
F=ma is a simplified version of how to obtain force. There are other kinds
of forces out there (magnetic, electrical, etc.).
Look in a physics textbook to get a better idea (and description) about all
kinds of forces. Good luck.
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Update: June 2012