Free Fall

Do now: Calculate gravitational acceleration on earth

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!

Free Fall Mini Lesson: Doc Shuster (AP Physics) https://www.youtube.com/watch?v=Du_c6SIfJn8

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!!!!

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?

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

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

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

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)

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

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