Download Drawing Force Diagrams

Drawing Qualitative
Force Diagrams
Remember- qualitative means NO
NUMBERS.
You are just identifying the forces &
their directions on the diagrams.
Force Diagrams
Ex. 1: Draw the forces on a flamingo standing on the ground
1. Picture
2. Identify System
SYSTEM- the object
you are looking at
AKA the receiver of all
the forces
2. Identify System
The curve helps you
see the things in
contact with your
system. Any object
crossing the curve is
applying a contact
force on the system.
3. Closed curve
around system
4. Identify contact forces where
system touches the closed curve.
Any object that is touching
the receiver is applying a
contact force. In this
example, only the ground
is touching the flamingo
4a. Identify contact forces where
system touches the closed curve.
5. Normal
force,FN
4b. Identify
forces
4b.
Identify long-range
any field forces
5. Normal
force,FN
6. Force of
gravity, FG
7. Force
Diagram
5. Normal
force,FN
6. Force of
gravity, FG
FN
FG
ON-BY STATEMENTS….
FORCE NAME on RECEIVER by AGENT
7. Force
Diagram
5. Normal
force,FN
6. Force of
gravity, FG
FN
FG
Fn on the
flamingo by
the floor
Fg on the
flamingo by
the Earth
How to draw force diagrams:
1. Draw a circle around your system on the picture
2. Shrink your system into a dot and if the object is on a
slanted surface, draw a
showing the surface.
3. Identify objects crossing the system circle and
draw a contact force arrow for each.
4. Identify/draw arrows for all the field forces.
Ex. 2: Sled that is being pulled by a rope across
the ground.
Our system will be the sled. This means the sled is
the receiver for all the forces we draw.
The rope touches
the curve so it is
applying a contact
force on the sled
The ground touches the curve so it applies
contact forces to the sled- 1 to hold it up(Fn)
and 1 slowing its motion (Ff)
Field forces drawn
ON-BY STATEMENTS….
FORCE NAME on RECEIVER by AGENT
Fn on the sled by the
ground to hold it up
Ft on the sled by the rope
to pull the sled along
Ff on the sled by the
ground slowing it down
Fg on the sled by the
Earth
You drop your doll from the top of the
Eifel Tower.
Ignore air resistance!
No contact forces!
Fg is the only
push/pull on the
doll!
Fg
CANDY ?! Doll has a mass of 1 kg, how
much is the force due to gravity on her?
Ex. 3: Skateboard sliding down the rail
PAUSE….
Identify all the
forces you can ON
the skateboard
2. Define system: skateboard
3. Draw a closed curve
Draw a dotted line to show the surface.
That makes it is easier to draw in the correct
direction for normal & friction forces.
Although the boy has two feet,
we can draw his total weight as
one force downward.
Fn
Ff
How did you do?
Did you find all 4 forces?
Fw
Fg
Fn on the skateboard by the rail holding it up
Ff on the skateboard by the rail slowing it down
Fw on the skateboard by the boy
Fg on the skateboard by the Earth
STOP POWERPOINT HERE
More Practice Problems….
Ex: dog resists as you try to pull him for a walk 
7. Force
Diagram
5. (a)Normal
Force FN
5. (b)
Tension FT
FN
Ff
5(c). Friction Ff
6. Force of
gravity FG
FT
FG
A. An object lies motionless on
a rough inclined surface.
B. An object is
suspended from the
ceiling by two ropes
hung at an angle.
C. A leftward force is applied to a book in order
to move it across a desk at constant velocity.
Consider frictional forces. Neglect air resistance.
D. Draw the force diagram
for the bird.