Free Fall Notes Kinematics

Concept of Free Fall Free Fall motion of an object due ONLY the influence of gravity. Any object, regardless of it’s mass, falls near the surface of the earth with an acceleration of 10 m/s2 This will commonly be referred to as g, the force of gravity Ignore air resistance in equations.

Galileo Interactive Site Galileo’s Experiment Galileo was the first to show that falling bodies move with a constant acceleration. To prove his theory he dropped a feather and a hammer in a vacuum . His theory was proved on the Moon(little air resistance)! Galileo Interactive Site

This is commonly referred to as the Equations d = Vit + ½at2 D= displacement Vi=initial velocity T=time A=acceleration This equation explains how far an object travel, horizontally or vertically, based on how fast and how long the object traveled. If the initial velocity is at rest (0) you can take out the first part of the equation and you end up with this equation. d = ½at2 This is commonly referred to as the “free fall” equation.

Is it Free Fall? Tree Jump Felix Baumgartner‘ Cave of Swallows Cliff Jump

Numeric Values Acceleration due to gravity (g) -10m/s2 does not matter which way is positive and which way is negative, just as long as you are consistent. Use math grid Positive, up, above the x axis Negative, down, below the x-axis

Sample Problem If a stone took 15 seconds to hit the ground after being dropped from a cliff, from what height did it fall? What Formula (original) Final Answer   Manipulated (“flipped/flopped) Term ? # plugged in

Sample Problem If I drop a watermelon from the water tower in Hutto, and it takes 3.34 seconds to hit the ground, how tall the building is in meters? What Formula (original) Final Answer   Manipulated (“flipped/flopped) Term ? # plugged in

Sample Problem You are walking in Paris by the Eiffel Tower & suddenly a croissant smack you on the head & knocks you to the ground. You check your guidebook & find the height of the Eiffel Tower is 300.5 meters tall. Neglecting air resistance, how long did it take for the croissant to fall & hit you? What Formula (original) Final Answer   Manipulated (“flipped/flopped) Term ? # plugged in

Sample Problem Someone drops a penny from the Austonian, the tallest building in Austin, 208 meters. How long would it take the penny to fall to the street from the top of the building? WTF

Up & Down What happens if you throw something up in the air? You are going to use the same equation(s), d = Vit + ½at2 as for free fall, but you will need to include the initial velocity! Whether you are actually throwing something down or throwing something up. One thing that will be different is that you are going to have to double your time if you are asked how long will it take to return to its Your time is going to be double for it to reach back to the ground! d = Vit + ½at2

PRACTICE PROBLEM Suppose an object is thrown downward from the top of the tallest Sequoia tree in California’s Redwood National Park at a velocity of 5.0 meters/second and it takes 3.80 s to hit the ground. How tall is the tree?

PRACTICE PROBLEM The tallest roller coaster in the world is the Desperado in Nevada. It has a lift height of 64 m. If an archer shoots an arrow straight up in the air and the arrow passes the top of the roller coaster 3.0 s after the arrow is shot, what is the initial speed of the arrow? How long does it take the arrow to go up and then come down to the ground?