1. Air Resistance and Free Body Diagrams
Notes: Air Resistance and Free Body Diagrams

2. Notes: Free Body Diagrams (copy in your notes)
Free body diagrams: diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
The forces acting on an object are represented by arrows.
The size of the arrow in a free-body diagram reflects the magnitude of the force. The direction of the arrow shows the direction that the force is acting.

3. Example: Free Body Diagram
In a free-body diagram represent the object by a box
Draw the force arrow from the box outward in the direction that the force is acting.
What is the only force acting on an object in free fall?
Which direction does it act?
F (gravity)

4. Example: Free Body Diagram (copy in your notes)
You must ALWAYS label the arrows representing forces on your diagram.
Your label will be in the following format:
F (name of your force)
F (gravity)

5. Air Resistance (copy in your notes)
A force that acts in opposition to the relative motion of an object through the air.
Which direction does an object move when it is falling?
In which direction will air resistance act on a falling object?

6. Free Body Diagram: Falling Object
What force causes the cow to fall?
What force acts in the opposite direction as the cow falls?
Which arrow is bigger?
Why?

7. Light as a feather…
Draw a free body diagram for a feather falling on the moon.
Draw a free body diagram for a feather falling on earth.

8. Hammer Time Draw a free body diagram for a hammer falling on the moon.
Draw a free body diagram for a hammer falling on earth.

9. Falling Objects: On the Moon Which one will hit the ground first?

10. Notes: Types of Forces
Gravitational Force: The force with which a massive object attracts another object towards itself (weight)
Air Resistance Force: A special type of frictional force that acts on objects as they move through the air.

11. Notes: Types of Forces
Applied Force: A force applied to an object by a person or another object.
Normal Force: The support force exerted upon an object that is in contact with another stable object.
Frictional Force: The force exerted by a surface as an object moves across it.
Tension Force: A force transmitted through a string, rope, cable or wire when it is pulled tight.

12. Which Forces?

13. Which Forces?

14. Which Forces?

15. Which Forces?

16. Which Forces?

17. Notes: Steps for Free-Body Diagrams
Homer is sitting on the ground.
1. Draw a box.
2. Is the object accelerating?
If yes, forces are unbalanced.
If no, the forces are balanced.
3. Identify all the forces acting on your object.
4. Draw and label your arrows.

18. Notes: Using Net Force to Describe Motion
NET FORCE = 0 Newtons
When forces are equal and opposite the object is at CONSTANT VELOCITY.
If forces are unequal the object is ACCELERATING in the direction of the larger arrow/force.
Acceleration in the direction of net force. /

19. Notes: Net Force
Net force is the sum of ALL the forces acting on an object.
If forces are acting in opposite directions:
Find the difference between the two forces.
If the net force is greater than zero you must give the direction of the net force.
EXAMPLE:
Net Force = F (air resistance) – F(gravity)
= 500N – 500N = 0 N
F (air resistance) = 500N
F (gravity) = 500N

20. Practice: Net Force
F (gravity) = N

21. Practice: Net Force
air

22. Practice: Net Force

23. Notes: Using Net Force to Describe Motion
NET FORCE = 0 Newtons
When forces are equal and opposite the object is at CONSTANT VELOCITY.
If forces are unequal the object is ACCELERATING in the direction of the larger arrow/force.
Acceleration in the direction of net force. /

24. Homework: Free Body Diagrams