Net Forces Learning Goals
Determine the net force actingon an object. Define equilibrium. Draw free-body diagrams torepresent all forces acting on abody. Forces and Equilibrium
The sum of all the forces on anobject is called the net force. The word net means total but alsomeans the direction of the forceshas been taken into account. In what direction will this plane go? Adding forces To figure out if or how an objectwill move, we look at ALL of theforces acting on it. Four forces act on a plane: weight drag (air friction) the thrust of the engines, and the lift force caused by the flow of air over the wings. Equilibrium When several forces act on the same object:
The net force iszero, or The net force isNOT zero. Normal forces When the forces are balanced, the net force is zero.
When the net forceon an object iszero, we say theobject is inequilibrium. Equilibrium and normal forces
A normal force iscreated whenever anobject is in contactwith a surface. The normal force hasequal strength to theforce pressing theobject into the surface,which is often theobjects weight. The normal force is sometimes called the support force. The free body diagram How do you keeptrack of manyforces with differentdirections? Draw a free-bodydiagram thatcontains theobjects, like a bookon a table. Solving equilibrium problems
For an object to be in equilibrium,all the forces acting on the objectmust add up to zero. Is this object in equilibrium? Two chains are used to support a small boat weighing 1,500 newtons.
Solving Problems Two chains are used to support a small boat weighing 1,500 newtons. One chain has a tension of 600 newtons. What is the force exerted by the other chain? Solution: Solving Problems Draw free body diagram
Upward force of chains = weight of boat 600 N +tension2=1,200 N tension2 = 900 N