Do Now 10 Minutes Topic Free Fall I will be passing out a pop quiz right now. You have ten minutes to complete the pop quiz.
Homework Complete the Motion Graph Lab Turn in the Kinematic Equations Worksheet (1 Day Late) Due 10/24/14
Free Fall Imagine the following situation: I am up in a tree about 4 meters above you, and I drop a can of soda down to you. Now imagine that I am on top of the Empire State Building. I drop a can of soda down to you. What s the difference between these two situations? Which can of soda would you rather catch? Why?
Free Fall From your life experience, do objects fall at a constant speed, or do they speed up more and more when they re falling for a longer period of time? The more time an object spends falling, the faster it travels!
Free Fall An object moving under the influence of only the gravitational force is said to be in free fall. The more time an object spends in free fall, the faster the object goes. How quickly do objects accelerate while under the influence of gravity?
Free Fall The acceleration of an object in free fall is about 9.8 meters per second squared. (9.8 m/s 2 ) We use the variable, g, to denote gravity. Technically, depending on where you are on Earth, the pull of gravity varies from 9.8 m/s 2, but the general assumption is that gravity pulls at a constant rate.
Misconception!! Some people think that heavier objects fall faster than light objects. These people are incorrect, as we see with this demonstration. (Set of masses) Gravity is not affected by mass.
Free Fall Another thing to consider: In the absence of air resistance, objects will fall at the same rate. We can see this in the following video from Apollo 15 where astronauts dropped a hammer and feather at the same time.
Red Bull StratosJump Two years ago, on October 14, 2012, Austrian Skydiver Felix Baumgartner became the first human to break the sound barrier without an engine. How did it he do it? Let s see.
Free Fall Problems Some things to note: 1. Whenever we are dealing with objects in free fall, the object will always accelerate due to gravity (9.8 m/s 2 ) 2. All of our kinematic equations that we learned all hold true in free fall problems.
Sample Problem Felix Baumgartner traveled at speeds upwards of 340 m/s (the speed of sound) If Felix fell under the effects of gravity, how long did it take him to reach the speed of sound? What distance did he travel in order to break the sound barrier?
Sample Problem Mr. Fineman drops a can of soda from the top of a tree (4 m tall) How long does it take for the can to hit the ground? What is the speed of the can before it hits the ground?
Sample Problem Mr. Fineman drops a can of soda from the top of the Empire State Building (381 m tall) How long does it take for the can to hit the ground? What is the speed of the can before it hits the ground?
Sample Problem A skydiver hits terminal velocity when he reaches a speed of 56 m/s. How long does it take for the skydiver to reach terminal velocity? What distance does the skydiver fall during the period time?
Hang Time All of our problems, thus far, have involved objects dropping from some height. If we toss an object up, it will eventually come back down. The time an object spends going up then coming down is known as hang time.
Hang Time As an object travels upward, gravity is constantly pulling it down. This slows the object. At the top of its path, the object s instantaneous velocity is equal to 0 m/s. Its acceleration remains 9.8 m/s 2
Hang Time As we see from this picture, the speed of the object is equal at corresponding sides of the arc. The speed in which an object comes back to your hand is equal to the speed in which you threw it! Sample problem: v i = 29.4 m/s
Hang Time The time spent going up is equal to the time spent coming back down. In a hang time problem, time up = time down. THIS IS VERY IMPORTANT!!!!
Hang Time Problems In hang time problems, students often ignore what the problem is asking and just smash numbers together in their calculators to get an answer. You need to pay attention to what is being said in a hang time problem.
Hang Time Problems A student throws a pen up in the air. It takes 0.25 seconds to reach the top of its arc. How long does it take for the pen to return to the student?
Hang Time Problems A baseball player throws a ball from the outfield to home plate. The ball takes 5 seconds to go from the outfield to home. How much time is the baseball going up? How much time is the baseball going down?
Hang Time Problems What speed must you toss a ball straight up so that it takes 5 seconds to return to you?
Hang Time Problems If a rocket is fired straight up at a speed of 98 m/s, what is the total time it takes to return to the ground?