an introduction to acceleration: more practice
TRANSCRIPT
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration: More Practice
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An Introduction to Acceleration:More Practice
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An Introduction to Acceleration: More Practice
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Gravity and Free-Fall: Student Learning Goals
Students will conduct an inquiry to measure gravitational acceleration, and calculate the percentage error of their experimental value (B2.3, B2.10)
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Gravity and Free-Fall
SPH4C
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g
The acceleration due to the Earth’s gravity is
9.8 m/s2 [down].
The magnitude of this acceleration is denoted by the letter g.
132
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Up, then Down
An object feels this acceleration when travelling up (when it slows them down) and when travelling down (when it speeds them up).
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Mass doesn’t matter
Note that all objects, regardless of mass, experience the same acceleration.
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Galileo
This discovery is attributed to Galileo.
http://www.youtube.com/watch?v=5C5_dOEyAfk
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Drag
However, some objects are slowed by atmospheric drag more than others.
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Terminal velocity
At a given speed, the drag will equal the gravity, and the object will stop accelerating, i.e. reach “terminal velocity.”
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Terminal velocities
Typical terminal velocities:
Human 53 m/s (190 km/h)
Human with parachute 5 m/s (18 km/h)
Dandelion seed 0.5 m/s (1.8 km/h)
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The fastest man
On August 16th, 1960 U.S. Air Force Captain Joe Kittinger broke the sound barrier (1240 km/h) during a free-fall from the high altitude balloon Excelsior III, at an altitude of approximately 31 km.
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Highest fall survived (without a parachute)
Flight attendant Vesna Vulovič fell 10,000 m on January 26, 1972 when she was aboard a plane that was brought down by explosives over the Czech Republic.
She suffered a broken skull, three broken vertebrae (one crushed completely), and was in a coma for 27 days, but she survived!
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g’s
Accelerations are often given in terms of g.
For example,
4 91
9 852
2
ms m
s
gg
.
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Blackout
A typical person can handle about 5 g before loss of consciousness, “blackout,” occurs.
The record for the most g forces on a roller coaster belongs to Mindbender at Galaxyland Amusement Park in Edmonton, Alberta, at 5.2 g.
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Greyout
Through the combination of special g-suits and efforts to strain muscles —both of force blood back into the brain— modern pilots can typically handle 9 g or more.
They may experience a “greyout” (temporary loss of colour vision, tunnel vision, or an inability to interpret verbal commands) between 6 and 9 g.
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Negative g’s
Resistance to "negative" or upward g’s, which drive blood to the head, is much less (typically in the -2 to -3 g range).
During “redout,” vision goes red, probably due to capillaries in the eyes bursting under the increased blood pressure.
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“g-Force”
Acceleration perpendicular to the spine is more tolerable.
Acceleration pushing the body backwards (“eyeballs in”) is tolerable up to 17g, and pushing the body forwards (“eyeballs out”) up to 12g.
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Strongest g-forces survived
Voluntarily: Colonel John Stapp in 1954 sustained 46.2 g in a rocket sled, while conducting research on the effects of human deceleration
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Strongest g-forces survived
Involuntarily: Formula One racing car driver David Purley survived an estimated 178 g in 1977 when he decelerated from 173 km/h to 0 in a distance of 66 cm after his throttle got stuck wide open and he hit a wall
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Everyday g-forces
Coughing: 3.5 g
Sneezing: 2.9 g
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Free fall
Objects in free-fall feel
0 g, or “weightlessness.”