FREE FALLING BODIES

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FREE FALLING BODIES
GALILEO GALILEI (1564 1642)
? Italian astronomer physicist
? Father of Experimental Science
Source http//www-groups.dcs.st-and.ac.uk/histor
y/PictDisplay/Galileo.html
? Supported the Heliocentric Theory of Nicolaus
Copernicus
? Invented the first telescope, thus the first
person to look at the Moon through a
telescope
? Discovered the four moon circling Jupiter
LAWS OF PENDULUM
http//scienceworld.wolfram.com/biography/Galileo.
html http//inventors.about.com/library/inventors/
blgalileo.htm
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GALILEO VERSUS ARISTOTLES LAWS OF NATURE
ARISTOTLE
?Born 384 BC Died322 BC
? Greek philosopher, mathematician scientist
?Father of Science
? Systematized deductive logic/reasoning
? determined the orientation and the content of
Western intellectual history. Western culture was
Aristotelian.
? Proponent of the laws of nature
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ARISTOTLES ASSUMPTIONS
There is a natural place for everything to seek,
asHeavy things go downward, Fire upward,And
rivers to the sea - Aristotle
It was in the nature of falling, said Aristotle,
that heavy objects seek their natural place
faster than light ones -- that heavy objects fall
faster.
Aristotle's word had been accepted as gospel
truth, and there had been few attempts to
actually test Aristotle's conclusions by actually
conducting an experiment!
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GALILEOS EXPERIMENT IN THE LEANING TOWER OF PISA
Aristotles Assumption Heavy Objects fall
faster then light ones
Galileos Experiment Drop two balls from the
tower (canon wooden ball)
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GALILEOS FINDING
HEAVY AND LIGHT OBJECTS FALL AT THE SAME TIME IN
THE ABSENCE OF AIR RESISTANCE OR AIR FRICTION
Suppose that an elephant and a feather are
dropped off a very tall building from the same
height at the same time.
Suppose that air resistance could be eliminated
such that neither the elephant nor the feather
would experience any air drag during the course
of their fall.
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In the absence of air resistance, the elephant
and the feather strike the ground at the same
time. Why is this so?
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MOTION OF FREE FALLING BODIES
A free-falling object is an object which is
falling under the sole influence of gravity.
Any object which is moving and being acted upon
only by the force of gravity is said to be "in a
state of free fall.
All objects (regardless of their mass) experience
the same acceleration when in a state of free
fall.
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FREE FALLING BODY
Free-falling objects do not encounter air
resistance.
All free-falling objects (on Earth) accelerate
downwards at a rate of approximately 10 m/s2
or to be exact, 9.8 m/s2.
Thus, g 9.8 m/s2 is also known as acceleration
due to gravity.
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EQUATIONS OF MOTION APPLIED TO FREE FALLING BODIES
? Vf Vi gt
Since Vi 0 then the formula can be written as
Vf gt
Problem 1Mitch forgot his key to her locker in
school. She asked her sister to drop it on their
window so she does not need to go upstairs again.
How fast will the key fall from the window if it
reached the ground in 10 seconds?
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SOLUTION
Vf Vi gt or Vf gt
g 9.8m/s2 The key is a free falling body
Thus, Vf (9.8m/s2)(10 s)
Vf 98m/s ? final velocity of key
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Problem 2 A patient accidentally dropped off
from the rooftop of a hospital. The body hit the
ground in 6 sec. How high is the building of the
hospital?
? d Vit ½ gt2 or d ½ gt2
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SOLUTION
d Vit ½ gt2 or d ½ gt2
d ½(9.8m/s2)(6s)2
d 176.4 meters
Thus, the hospital is 176.4 meters tall
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Problem 3 An object falls from an airplane at an
altitude of 12000meters at a final velocity of
20m/s. How long will the object hit the ground?
HOW WILL YOU SOLVE THE NEXT PROBLEM?
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Exercise 11Free Falling bodies
Solve the following problems completely!

1. An object dropped from a cliff 100 meters above
   the ground. How long will it take the object to
   reach the ground? What is the final velocity of
   the object?
2. A hospital building is 200 meters high. If a
   dextrose bottle is dropped from its top, what
   will be the velocity as it reaches the ground?
   How many seconds will it reach the ground?
3. The time it took for a ball to reach the ground
   is 40 seconds. If the ball has a final velocity
   of 1.5 m/s then how much distance was covered by
   the ball?
4. Find the final velocity of a shooting star that
   fell on the surface of the earth in 25 minutes.
5. Find the time it will take a shooting star to
   reach the surface of planet earth if the distance
   above the ground it will travel is 5000
   kilometers.