Weightlessness, G-Force,
Inertia and Centripetal Force
Puzzler
• Astronauts on the orbiting space shuttle are
weightless because...
a)there is no gravity in space and they do not weigh
anything.
b)space is a vacuum and there is no gravity in a
vacuum.
c) space is a vacuum and there is no air resistance in a
vacuum.
d)the astronauts are far from earth's surface at a
location where gravitation has a minimal effect.
e)the astronauts are in free-fall, are traveling fast
enough sideways to miss the Earth and are receiving
no support force.
13.8 Weight and Weightlessness
The sensation of weight is equal to the force that you exert
against the supporting floor.
13.8 Weight and Weightlessness
The condition of weightlessness is not the absence of gravity,
but the absence of a support force.
In other words, you are as heavy as you feel.
13.8 Weight and Weightlessness
Both people are without a
support force and therefore
experience weightlessness.
g-forces
• g-forces: the force that your body is subjected to
when accelerated.
• 1 g is your weight either at rest or at a constant
velocity
• Greater or less than 1 g means you are
accelerating (changing speed and/or direction)
• > 1 g is a sensation of greater than your weight
• < 1 g is a sensation of less than your weight
• 0 g is apparent weightlessness
G-force
• 1g
normal weight
• more or less than 1 g results when the
object accelerates by changing direction
either up or down.
• 0 g ("weightless") what an object in free
fall experiences; no support force.
• 2 g (twice normal weight) object
http://www.youtube.com/watch?v=aSVfYwdG
https://www.youtube.com/watch?v=2V9h42
SsQ&feature=related
yspbo
Mythbusters rocket sled
http://www.youtube.com/watch?v=VkcSsZttux
g&feature=related
Col. Stapp space g-force testing
http://www.youtube.com/watch?v=3UEYxf4fl_A&playnext=1&list=PL74F9F94AB5F4D54E
Col Stapp space g-force testing
http://www.youtube.com/watch?v=s4tuvOer_GI
Col. Stapp History Channel g-force testing
http://www.youtube.com/watch?v=ynsyZ0f_8GI
Steve are you with me
https://www.youtube.com/watch?v=Yjg6mRFzZzE
https://www.youtube.com/watch?v=TGHvFpNCrtQ
Questions
• In what direction are Gz forces
experienced?
• Approximately how many seconds pass
before serious effects of large g-forces are
observed?
• Approximately how much g-force produces
a cardiovascular reflex?
Directions of g-forces
g-forces
• The effect of g-force on the human body
depends upon the amount of g-force , the
amount of time that you endure the g-force
and the direction that the g-force is felt.
• http://www.c00lstuff.com/1974/Pulling_G_
s/ (Steve, are you with me? –g-force and
jet fighters)
Examples of g-forces
•
•
•
•
NASCAR driver (up to 5 gs in a turn)
Astronaut (2-4 gs)
Fighter pilot (4-6 gs, up to 9 gs)
Amusement Park Ride with highest g
forces (6 g per second)
• Your ability to handle g-forces is based on
the g-force and the amount of time you
experience it.
Difference between positive and
negative g-forces
• Positive G force will push the blood in your body towards your
feet and resist your heart's attempts to pump it back up to your
brain. You will begin to get tunnel vision, then things will lose
color and turn white, and finally everything will go black.
Negative Gs will push the blood up into the head, just the
opposite of positive Gs. However, while the body can stand up
to 9 positive Gs without severe consequences, blood vessels
in your eyes will start to rupture when you apply as little as 2 to
3 negative Gs. This is known as redout.. A pilot who pushes
too many negative Gs will be seeing the world through
bloodshot eyes.
Here's a handy little G-force table:
Ultracentrifuge 300,000 G
Baseball struck by bat 3000 G
Soccer ball struck by foot 300 G
Automobile crash (100 km/h into wall) 100 G
Parachutist during opening of parachute 33 G
Gravity on surface of Sun 27 G
Explosive seat ejection from aircraft 15 G
F16 aircraft pulling out of dive 8 G
Loss of consciousness in man ("blackout") 7 G
Gravity on surface of Earth 1 G
Braking of automobile 0.8 G
Gravity on surface of Moon .17 G
• http://www.pbs.org/wgbh/nova/space/gravityforces.html
12.6 Simulated Gravity
How is gravity simulated?
Centripetal Motion Applications
• http://www.glenbrook.k12.il.us/gbssci/phys
/mmedia/circmot/cf.html
• http://www.glenbrook.k12.il.us/gbssci/phys
/mmedia/vectors/sat.html
• http://sol.sci.uop.edu/~jfalward/physics17/
chapter4/chapter4.html
Centripetal Force
• Any force that causes an object to turn
• Centripetal force is directed towards the center of
rotation: keeps the object from taking an inertial
path
Examples:
• Gravity
– moon orbits earth
• Friction
– Car turns on road
• Applied by structure
– Roller coaster loops
Centripetal Force Questions
on loose leaf-turn in
1. Define centripetal force
2. What role does centripetal force play in
the motion of an object?
3. Why is centrifugal force an apparent or
false force?
Inertia and Centripetal Force
• What causes a car on a roller coaster
track to turn and how is inertia related?
Inertia and Centripetal Force
• “An object keeps moving in a straight line
at the same speed unless a an
unbalanced force stops it from doing
that. The track causes the roller coaster
car to change direction by applying a
centripetal force. If the loop did not apply
this force, then the car would continue
move in a straight line due to its inertia.”
Page 182
• 8.inward, towards the center of the circle.
• 9. inward
• 11. lack of force: the object continues in a
straight line tangent to its circular path as
the centripetal force is directed inward
providing the net force needed to cause it
to turn.
Centripetal force vs. Centrifugal “Force”
The centripetal
force is the
external force
required to make
a body follow a
curved path
An object traveling in a circle behaves as
if it is experiencing an outward force, but
it is not a real force.
Centrifugal force is the “force” you feel as
you turn is due to the tendency of a rotating
body to keep moving in a straight-line path.
You are actually experiencing redirection
due to an inward centripetal force.
Centripetal Force: identify the cause of
centripetal force
Car turning
around a curve
Loop on a roller coaster
Centripetal Force: identify the cause of
centripetal force
Earth’s Orbit
Revolution of a ball
on a string
12.6 Simulated Gravity
From within a rotating frame of reference, there
seems to be an outwardly directed centrifugal force,
which can simulate gravity. Note: centrifugal force is
not really a force; it is an apparent force due to inertia.
http://www.daviddarling.info/encyclopedia/A/artgr
av.html
12.6 Simulated Gravity
The man inside this rotating space habitat experiences
simulated gravity.
a. As seen from the outside, the only force exerted on
the man is by the floor.
12.6 Simulated Gravity
The man inside this rotating space habitat experiences
simulated gravity.
a. As seen from the outside, the only force exerted on
the man is by the floor.
b. As seen from the inside, there is a fictitious
centrifugal force that simulates gravity.
12.6 Simulated Gravity
If the spinning wheel freely falls, the ladybugs inside will
experience a centrifugal force that feels like gravity when
the wheel spins at the appropriate rate.
12.6 Simulated Gravity
Small-diameter structures would have to rotate at high speeds
to provide a simulated gravitational acceleration of 1 g.
Sensitive and delicate organs in our inner ears sense rotation.
Although there appears to be no difficulty at 1 RPM, many
people have difficulty adjusting to rotational rates greater than
2 or 3 RPM.
To simulate normal Earth gravity at 1 RPM requires a large
structure—one almost 2 km in diameter.
Stanford Torus
The Stanford torus is a proposed
design for a space habitat
capable of housing approximately
10,000 to 140,000 permanent
residents. It consists of a torus or
donut-shaped ring that is 1.8 km
in diameter (for the proposed
10,000 person habitat described
in the 1975 Summer Study) and
rotates once per minute to
provide between 0.9g and 1.0g of
artificial gravity on the inside of
the outer ring via centripetal
acceleration.
http://www.answers.com/topic/artificial-gravity
Here's a handy little G-force table:
Ultracentrifuge 300,000 G
Baseball struck by bat 3000 G
Soccer ball struck by foot 300 G
Automobile crash (100 km/h into wall) 100 G
Parachutist during opening of parachute 33 G
Gravity on surface of Sun 27 G
Explosive seat ejection from aircraft 15 G
F16 aircraft pulling out of dive 8 G
Loss of consciousness in man ("blackout") 7 G
Gravity on surface of Earth 1 G
Braking of automobile 0.8 G
Gravity on surface of Moon .17 G
• http://www.pbs.org/wgbh/nova/space/gravityforces.html