1. Gravity and Freefall

2. The Law of Gravitation
You exert an attractive force on everything around you and everything is exerting an attractive force on you.
2. This attractive force is called gravity.
3. Anything that has mass is attracted by the force of gravity.
4. The Law of Gravitation states that any two masses exert an attractive force on each other.

3. The Law of Gravitation 5. Gravitational force depends on two things:
The mass of the two objects
The distance between the two objects
6. Why do you suppose the Earth exerts a force on you that you can feel, but you can’t feel the force the desk is exerting on you?

4. The Mathematical Relationship
7. The greater the mass of either object, the greater the attraction (Fg).
8. The greater the distance between the objects, the smaller the attraction (Fg). or

5. The Inverse square law:
9. Since the distance (d) is in the denominator of this relationship, it can be said that the force of gravity is inversely related to the distance.
10. And since the distance is raised to the second power, it can be said that the force of gravity is inversely related to the square of the distance.

8. Gravitational Acceleration
11. When objects fall, the gravitational pull is
9.8 m/s2
(sometimes rounded to 10 m/s2)
12. When a falling object is only affected by gravity it is said to be in free fall.

9. Gravitational Acceleration
If you drop a a feather and a coin, which will hit the ground first?
How about if there was no air?

10. FORCE? A bowling ball? Or a marble?
13. Okay, Which has more gravitational
FORCE?
A bowling ball?
Or a marble?
14. Force of gravity is greater on the bowling ball because of its larger mass.
Remember, Fg= m x g

11. 15. The larger mass means it has a larger inertia so more force is needed to change its velocity.
16. Gravitational force on the marble is smaller because it has a smaller mass.
17. The inertia on the marble is less and less force is needed to change its velocity.
18. Therefore, all objects fall with the same acceleration!

12. Air Resistance What two forces are acting on an object when it falls?
19a. Gravity
19b. Air resistance

13. Air Resistance
Imagine dropping two pieces of paper. One is crumpled and the other is flat.
Which one will reach the ground faster and why?
20. The crumpled one because it has less surface area.

14. Air Resistance
When something falls, air resistance acts in the opposite direction to the force of gravity.
22. Air resistance acts in the opposite direction of the object’s motion.

15. Air Resistance
The amount of air resistance an object experiences depends on two things:
23 a. Speed
23 b. Surface Area

16. Air Resistance
Why do leaves, papers, and feathers fall at different speeds than acorns, pens, and glasses?
Because of Air Resistance…
24. Air resistance, not mass, is responsible for the differences in the speeds of falling objects.

17. Terminal Velocity
25. As an object falls, it accelerates and its speed increases.
26. The force of air resistance increases with speed.

18. Terminal Velocity
27. The force of air resistance increases until it becomes large enough to cancel the force of gravity.
When the forces cancel each other out the object no longer accelerates. It is in EQUILIBRIUM!
28. The object then falls at a constant speed - called terminal velocity.

19. Terminal Velocity
29. Terminal Velocity is the highest velocity that a falling object will reach.
30. A low terminal velocity allows a skydiver to land safely.

20. Terminal Velocity
30. Why would a skydiver want to lay out flat versus falling standing up?
Think about our paper example… crumpled vs flat
Point Break Clip!