1. Let’s begin with some skydiving movies.
Types of Forces
Let’s begin with some skydiving movies.

2. Gravity

3. Friction

4. Air Resistance ① Definition
Air resistance is the FORCE that OPPOSES the motion of another object through the air.

5. Predict Observe Explain ② ③ ④
Your teacher (or a volunteer) is going to drop
two pieces of paper: one piece of paper is flat
and the other is crumpled up.
Which piece of paper is going to hit the ground first? ②
Predict ③
Observe ④
Explain

6. ⑤
Draw arrows and label the force of gravity (Fg) and the force of air resistance (Far)
Far Fg

7. ⑥
Terminal Velocity
Terminal velocity is the CONSTANT velocity (speed) that a falling object reaches when GRAVITY and AIR RESISTANCE are balanced.

8. ⑦
The two forces acting on a skydiver jumping out of an airplane are GRAVITY and AIR RESISTANCE.   

9. ⑧
Draw arrows and label the force of gravity (Fg) and the force of air resistance (Far).
Far
ANIMATION Fg

10. How would skydiving be different on the Moon?Fg

11. ⑨ The Moon has no ATMOSPHERE (no air).
Therefore there is NO air resistance on the Moon.

12. ⑩
Empty space (a place with no air)
is called a VACUUM.

13. ⑪
What will happen if a flat piece of paper and crumpled piece of paper
are dropped at the same time on the Moon? Will one piece land first?

14. ⑫
FREE FALL is the name given to objects falling that experience the force of gravity but no air resistance.
Simulation of Galileo’s free fall experiment...ignoring air resistance.

15. NORMAL FORCE ⑬ The symbol for NORMAL FORCE is FN
Normal force is a force (usually a push) that
is PERPENDICULAR to the surface of contact.
The symbol for NORMAL FORCE is FN

16. Perpendicular means ⑭ AT RIGHT ANGLES or AT 90 DEGREES.
DEFINITION:

17. Push against a wall. Draw an arrow and label the normal force⑮
Push against a wall. Draw an arrow and label the normal force FN

18. The force a table exerts on a book.FN

19. ⑯ Comparing normal force to friction:
Friction force is PARALLEL to the contact surface.
Normal force is PERPENDICULAR to the
contact surface.

20. ⑰
Tension Force
The pull of a ROPE or STRING is called a TENSION force.
The symbol for the force of tension is FT

21. ⑱ Spring (Elastic) Force The pull or push of a SPRING, RUBBER BAND, or
BOUNCY BALL is called SPRING FORCE.
The symbol for the spring force is Fs

22. Now let’s try Identifying Interactions in Realistic Situations