Transcript Free Fall - Angelfire

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.
The
The
Experiment
Experimentatat
the
theLeaning
Leaning
Tower
Towerof
ofPisa
Pisa
By dropping a heavy
stone and a light stone
together, Galileo Galilei
proved that they
accelerate and land at
the same time.
So, what
explains
this????
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.GIF
www.ateneo.edu