Force - push or pull
 represented by F (always capital)
 measured in Newtons (N) in metric
system
 Vector quantities

› Amount (number value with units)
› Direction (N, S, W, E, up, down, etc.)

Represented by arrows – the larger the
force the longer the arrow
Free Body Diagrams
 Show all forces acting on an object
 Represent the object as a dot
 All forces start at the dot
Example: A 400 N wheelbarrow is being
pushed at an angle of 30˚ above the
horizontal with 30 N of force.
Fground
Fapplied
Fground
Ffriction
Fapplied
Ffriction
Fgravity
(weight)
Fgravity
(weight)
All of the forces acting on an object can
be combined into one force – the net
force.
 The net force is a single force that has
the same effect that the individual
forces had when acting together
 Fnet = net force

Forces in the same direction add
Example:
15 N
25 N
40 N
net Force
**When forces are in the same direction
the net force is maximum
When forces are applied with each other
(in the same direction) the overall effect is
a larger push
Forces in opposite directions subtract
Example:
15 N
25 N
10 N
net Force
**When forces are in opposite directions
the net force is minimum
When forces are applied against each
other (opposite directions), the overall
effect is a smaller push
When forces are at right angles to each other,
the net force (Fnet) can be determined using
Pythagorean Theorem (a2+b2=c2)
example:
Fnet
15 N
25 N
a2+b2=c2
(15N)2+(25N)2 = c2
225 +625 = c2
√ c2 = √ 850
c = 26.93 N = Fnet
• Make sure the individual forces are connected in one continuous path!!
• Forces are vectors…Don’t forget the direction (arrowhead)!!
Using a diagram, the direction of the net force
(Fnet) can be determined no matter which way
the individual forces are pointing
In order to draw the net force:
F3
F1
1. Move the individual forces around until
they are connected in one continuous
path
** Make sure to keep the size and
direction of each force the same
2. The net force connects the open tail to
the open tip
F2
Fnet
F2
F3
F1