Free body Free body diagrams and diagrams and FRICTIONFRICTIONHow do I calculate forces How do I calculate forces accurately?accurately?

FBD – The Best Motion FBD – The Best Motion PicturePicture

BoxBox ArrowArrow LabelLabel 6.0 N 2.0 N

Note: the 6.0N arrow is about 3 times longer than the 2.0N arrow

Which way does the Which way does the object move?object move?

Are the forces balanced?Are the forces balanced? Where does the imbalance lie?Where does the imbalance lie?

6.0 N 2.0 N

FFnetnet= F= F11+F+F22

-6.0N + 2.0N = F-6.0N + 2.0N = Fnetnet

-4.0N = F-4.0N = Fnetnet

6.0 N 2.0 N

-4.0N

Norm L. Force Norm L. Force The BalancerThe Balancer

Normal forces oppose Normal forces oppose applied forces (like gravity).applied forces (like gravity).

We don’t fall through our chairs thanks to We don’t fall through our chairs thanks to the normal force.the normal force.

Friction eats up some of Friction eats up some of the applied force.the applied force.

Static friction – when you are trying to Static friction – when you are trying to start pushing something.start pushing something.

Kinetic friction – when it is already in Kinetic friction – when it is already in motion.motion.

Friction eats up some of Friction eats up some of the applied force.the applied force.

(F(Fff) = u(F) = u(Fnn))