Drawing Qualitative Force Diagrams Remember qualitative means NO

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

SYSTEM- the object you are looking at AKA the receiver of all the forces

The curve helps you see things in contact with your system. Any object crossing the curve is applying a contact force on the system.

Any object that is touching the receiver is applying a contact force. In this example, only the ground is touching the flamingo

4 b. Identify any field forces

ON-BY STATEMENTS…. FORCE NAME on RECEIVER by AGENT 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 ne showing the surface. i l slanted surface, draw a d e h das 1. Identify objects crossing the system circle and draw a contact force arrow for each. 1. 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 Fw How did you do? Did you find all 4 forces? 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

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.