1. Skydiving from space!! http://www.youtube.com/watch?v=FHtvDA0W34I
What can potentially go wrong?
Does his acceleration change?

2. Review: Newton’s 1st Law of Motion
Newton’s 1st Law of Motion is inertia:
“Every object continues in its state of rest, or a uniform speed in a straight line, unless acted on by a nonzero force.”

3. Newton’s 2nd Law of Motion
Newton’s 2nd Law of Motion states:
acceleration = force/mass

4. Homework Review
Questions?

5. Review What is the net force on the box? Magnitude = Direction = 5 N

6. Review What is the net force on the box? Magnitude = Direction = 4 N

7. Quiz Review What is the acceleration? a = F m a = 4 N / 2 kg
a = 2 m/s2
4 N

8. Review
The force of gravity between the moon and an object near its surface is much smaller than the force of gravity on the Earth. A bowling ball with a mass of 7.51 kg is pulled downward with a force of 12.2 N. What is the acceleration of the falling bowling ball on the moon?
m = 7.51 kg
F = 12.2 N
a = 12.2 N / 7.51 kg = 1.6 m/s2

9. Newton’s Laws of Motion
What is Freefall?
Freefall is when the force of gravity is the only force on an object.

10. Free Fall
Free fall really only occurs in a vacuum or in space where there is no air.
If we drop a rock and a feather off in a vacuum, which will hit the ground first?

11. Free Fall
If we drop a rock and a feather off in a vacuum, which will hit the ground first?
Galileo said they would hit the ground at the same time, but why?
m = 1 kg, F =10 N
m = .01 kg, F =.1 N
a = F/m
a = 10 N/1 kg
a = 10 m/s2
a = F/m
a = .1 N/.01 kg
a = 10 m/s2

12. Non-Free Fall Acceleration
Most often, we have to consider air-resistance for falling objects.
Air resistance, which is a force of friction, depends on two things:
Surface Area
Speed

13. Non-Free Fall Acceleration
Net Force = Weight – Air Resistance
As a skydiver falls faster and faster, the acceleration decreases because the air resistance increases as the speed increases.

14. Non-Free Fall Acceleration
Net Force = Weight – Air Resistance
When the air resistance increases enough, the net force becomes 0 and acceleration stops.
Does this mean the skydiver stops?
No! It means the skydiver is no longer gaining speed – this speed is the terminal velocity.

15. Non-Free Fall Problems
Mass = 85 kg
Diagram A
Force = 833 N
Mass = 85 kg
Acceleration = 833N/85kg
= 9.8 m/s2

16. Non-Free Fall Problems
Mass = 85 kg
Diagram B
Force = 833N – 350N = 483N
Mass = 85 kg
Acceleration = 483N/85kg
= 5.7 m/s2

17. Non-Free Fall Problems
Mass = 85 kg
Diagram C
Force = 833N – 700 N = 133N
Mass = 85 kg
Acceleration = 133N/85kg
= 1.6 m/s2

18. Non-Free Fall Problems
Mass = 85 kg
Diagram D
Force = 833N – 833N = 0N
Mass = 85 kg
Acceleration = 0 N/85kg
= 0 m/s2

19. How are you feeling about this concept?
Reflection
How well do you understand Newton’s 1st Law? How about his 2nd Law? How about
What can you do to improve your understanding?