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!

The Motion of Falling

Objects

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.

By dropping a heavy stone and a light stone

together, Galileo Galilei proved that they

accelerate and land at the same time.

The Experiment at the Leaning

Tower of Pisa

The Experiment at the Leaning

Tower of Pisa

So, what explains this????

• 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!!!

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)

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!

Air Jordan

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