Elusive Wealth Hold a peso bill so that the midpoint hangs between a friend’s fingers. Challenge your friend to catch it by snapping his fingers shut when you release it. The bill won’t be caught!
There was a young man who had heard, That a person could fly like a bird. To prove it a lie He jumped from the sky - His grave gives the date it occurred!
Why do objects fall? The force of gravity pulls down on all the objects here on earth. Because of this force, objects will tend to accelerate downwards
At what rate do objects fall? Regardless of mass, in the absence of air resistance, all objects fall at the same rate. Near the surface of the earth, this value is g = 9.8 m/s2. This value is known as the acceleration due to gravity.
The Experiment at the Leaning Tower of Pisa The Experiment at the Leaning Tower of Pisa By dropping a heavy stone and a light stone together, Galileo Galilei proved that they accelerate and land at the same time.
AIR RESISTANCE!!! • is the result of collisions of the object's leading surface with air molecules. • determined by the object’s speed and cross-sectional area
AIR RESISTANCE!!! Once the force of air resistance is as large as the force of gravity, a balance of forces is attained and the skydiver no longer accelerates. The skydiver is said to have reached a terminal velocity.
When only the force of gravity is acting on a falling object, the object is said to be in a state of free fall. When an object is in free fall, it changes its velocity by 9.8 m/s (approximately 10 m/s) every second.
…which explains why falling from the third floor of a building hurts more than falling from the remaining two or three steps down a flight of stairs!
EXPLANATION to ELUSIVE WEALTH It takes at least 1/7 second for the necessary impulses to travel from the eye to the brain to the fingers. But in only 1/8 of a second, the bill falls approximately 8 cm (from y = ½ gt2), which is half the length of the bill.
REACTION TIME You can compare your reaction time with that of a friend by catching a ruler that is dropped between your fingers. Let your friend hold a ruler. Position your fingers at the 0 cm mark of the ruler. Snap your fingers shut as soon as you see the ruler released. The number of centimeters that pass through your fingers depends on your reaction time. You can find your reaction time in seconds by solving y = ½ gt2.
Output • Distance ruler has fallen in cm: • Trial 1:_________ • Trial 2:_________ • Trial 3:_________ • Average: _______ • Average in m:__________ • Reaction Time • (Show calculations and correct units)
Air Jordan Basketball players, ballet dancers, and others who have developed an unusual jumping ability when leaping straight up seem to hang in the air in defiance of gravity. We say they have a long “hang-time” – the amount of time airborne with the feet off the ground. A common misconception is that the greatest jumpers have hang-times of more than 2 s. Surprisingly, the hang-time of the greatest jumpers is almost always less than 1 s!
HANG –TIME Stand facing a wall, and with feet flat on the floor and arms extended upward, make a mark on the wall at the top of your reach. Then make your jump and at the peak make another mark. The distance between these two marks measures your vertical leap. Use your ruler to measure this distance in cm. Convert to m. Calculate your time to reach the highest point. Double this time to get your hang-time.
Output • Vertical leap in cm: • Trial 1:_________ • Trial 2:_________ • Trial 3:_________ • Average: _______ • Average in m:__________ • Hang Time • (Show calculations and correct units)
Sources: www.physicsclassroom.com Conceptual Physics, 8th ed. by Paul Hewitt Physics for You, by Johnson www.mcwdn.org/SPACE/METEOR.GIFwww.ateneo.edu