1. Free Fall

2. Do now: Calculate gravitational acceleration on earth

3. Announcements Check Skedula/Pupilpath for your grades
People are failing due to missing labs and missing homework
Some people got scores of zeroes for not putting their name on their labs - speak to me after class on Friday if you think this is the case for you
On a lighter note, I posted a bunch of review materials for next week’s exam - you can also use the material to help with your homework!

4. Free Fall Mini Lesson: Doc Shuster (AP Physics)

5. Key points
Free Fall occurs whenever the only thing acting on an object is gravity (neglect air resistance)
Acceleration on earth is equal to g (‘baby g’), which is called gravitational acceleration and is equal to 9.8 m/s/s
Acceleration is always downward on earth because gravity always points downward on earth!!!!

6. Check for Understanding
A person throws a ball straight upward.
1. What is the acceleration at the very top of its trajectory?
2. What is its velocity at the very top of its trajectory?

7. Check for Understanding
A person throws a ball straight upward.
1. What is the acceleration at the very top of its trajectory? Acceleration = g = 9.8 m/s/s downward ALWAYS!
2. What is its velocity at the very top of its trajectory?
Velocity at the peak is 0 m/s because it stops for a moment before falling

8. Vocabulary for Word Problems
‘Thrown up’ implies that the object reached a final velocity of zero at the top of the trajectory
‘Dropped’ implies that the initial velocity of the object is 0 m/s (dropped as opposed to thrown downward)
Acceleration on earth is always g unless otherwise noted
‘Maximum height’ is talking about (vertical) distance

9. Example
1. A 1.0-kilogram ball is dropped from the roof of a building 40 meters tall. What is the approximate time of fall?
Answer: 2.83 seconds

10. Work Time
The same exact kinematic equations apply to these new problems but now we have more things that are implied
Note: You do not need to use all the information given to solve a problem. If you can solve the problem using less information than what was given, that is perfectly fine! (You do not have to use all the variables)

11. Mild
1. An astronaut drops a hammer from 2.0 meters above the surface of the moon. If the acceleration due to gravity on the moon is 1.62 m/s2, how long will it take for the hammer to fall to the Moon’s surface?
Answer: 1.6 seconds
2. A ball is thrown straight downward with a speed of 0.50 meter per second from a height of 4.0 meters. What is the speed of the ball 0.70 second after it is released?
Answer: 7.4 m/s
3. How far will a brick starting from rest fall freely in 3.0 seconds?
Answer: 44 m
4. A 1.0-kilogram ball is dropped from the roof of a building 40 meters tall. What is the approximate time of fall?
Answer: 2.9 seconds

12. Medium
A rock falls from rest off a high cliff. How far has the rock fallen when its speed is 39.2 meters per second?
Answer: 78.3 meters
An astronaut standing on a platform on the Moon drops a hammer. If the hammer falls 6.0 meters vertically in 2.7 seconds, what is its acceleration?
Answer: 1.6 m/s2
An object is dropped from rest and falls freely 20 meters to Earth. When is the speed of the object 9.8 meters per second
Answer: 1 Second