1. MORE ABOUT
FORCES

2. Net force & Free Body Diagrams
Net force = vector sum of the forces
acting on an object
Free Body Diagram (FBD) depicts the forces
Arrows point in direction of forces
Relative lengths of arrows show relative
magnitudes of forces

3. NET FORCE
Net = total
Net force is the vector sum of all the forces acting on an object.
Direction of the force matters! (Pay careful attention to + and – signs)

4. An example Consider the rabbit 2 forces act on it: Fnet=Fhand+W
Its weight pulls it downward
The magician’s hand holds it up
Fhand
Fnet=Fhand+W W

5. An example continued Fnet=Fhand+W Fnet= +30-19.6 Fnet = +10.4 N
Suppose the rabbit has a mass of 2 kg
What is its weight?
What sign can be used to indicate the direction that the weight acts?
Suppose the magician pull the rabbit out of the hat with a force of 30N
What is the net force on the rabbit?
Fhand=+30N
Fnet=Fhand+W
Fnet=
Fnet = N
W=mg
W= -19.6N

6. Equilibrium If the forces are balanced, the net force is on
an object is zero. We say that an object is
in equilibrium.
How would you expect an object that’s in equilibrium to ‘react’ to the forces acting on it?
How would you expect an object that’s not in equilibrium to ‘react’ to the forces acting on it?