1. Turn in homework
Pick up graded quizzes in bottom of turn in bin
Stop talking so much in class and pay attention

2. We will have lots of quiz grades so don’t stress too much.
Quizzes
Weren’t so great 
We will have lots of quiz grades so don’t stress too much.
This is your chance to mess up or realize you don’t know something before the test!

3. What Forces act to Keep the Earth Moving?
NOTHING
Inertia says an object in motion stays in motion
The sun just keeps us in orbit

4. Free Falling Objects Things fall because of the force of gravity… duh
When an object falls with no restraints (like friction with the air) and falls under the influence of gravity alone, the object is in a state of Free Fall
We will worry about air resistance in the next chapter

5. What is happening during each second of fall?
Time of Fall (s)
Velocity Acquired (m/s) 1 10 2 20 3 30 4 40 5 50
The object gains a speed of 10m/s

6. Our Old Friend Acceleration!
This gain per second is the acceleration.
For this scenerio, free fall accelerations is = 10m/s2
Why is the unit of time squared?
Time of Fall (s)
Velocity Acquired (m/s) 1 10 2 20 3 30 4 40 5 50
Because the object is falling at a speed of 10m/s PER second – so we just square s. It’s easier that way.

7. NO!!!! The moon has a different gravitational pull
For free fall, we use g to represent acceleration (because it is due to gravity)
Would g be the same on the surface of the moon?
NO!!!! The moon has a different gravitational pull

8. In this class we will use g = 9.8 m/s2

9. So How Do We Find The Velocity of a Free Falling Object?
v = gt

10. SILENTLY do this on your paper
If you drop a penny off of the empire state building because you are a no good scoundrel, and it takes 8 seconds to fall, what is the penny’s velocity when it hits the ground?
78.4 m/s
(that is about 175 mph)

11. What about a ball thrown straight in the air?

12. How do we Measure Distance Traveled?
Distance traveled d = ½ gt2

13. Justin Bieber falls off a ledge and drops to the ground in ½ a second
Justin Bieber falls off a ledge and drops to the ground in ½ a second. For the next few problems you can use g=10m/s since you don’t have a calculator

14. Justin Bieber falls off a ledge and drops to the ground in ½ a second.
What is Justin’s speed on striking the ground?
v=gt
10 m/s *1/2 s = v= 5 m/s

15. Justin Bieber falls off a ledge and drops to the ground in ½ a second.
b. What is Justin’s average speed during the ½ second
Just find the average!
0 +5/ Average Speed = 2.5 m/s

16. Justin Bieber falls off a ledge and drops to the ground in ½ a second
Justin Bieber falls off a ledge and drops to the ground in ½ a second. c. How high is the ledge from the ground? hint: not high enough is not the correct answer
d=1/2gt2
d = ½ * 10 m/s * (1/2)2 d=1.25m

17. Real Life
We notice that many objects fall at different accelerations (a feather vs. pencil)
It is because of air resistance – for right now we aren’t worried about this.
We just assume everything is in a vacuume where there isn’t air resistance!

18. Practice – You Have Until Tuesday!
Pg. 47 – review questions # 18-22, 24, 26
Plug and Chug # 13-22
There will be a quiz on Tuesday so don’t cheat… also DON’T CHEAT