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.

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.

13.8 Weight and 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

• 1 g 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

G-force

http://www.youtube.com/watch?v=aSVfYwdGSsQ&feature=relatedMythbusters rocket sled

http://www.youtube.com/watch?v=VkcSsZttuxg&feature=relatedCol. Stapp space g-force testing

http://www.youtube.com/watch?v=3UEYxf4fl_A&playnext=1&list=PL74F9F94AB5F4D54ECol Stapp space g-force testing

http://www.youtube.com/watch?v=s4tuvOer_GICol. Stapp History Channel g-force testing

http://www.youtube.com/watch?v=ynsyZ0f_8GISteve are you with me

https://www.youtube.com/watch?v=Yjg6mRFzZzE

https://www.youtube.com/watch?v=TGHvFpNCrtQ

https://www.youtube.com/watch?v=2V9h42yspbo

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/gravity-forces.html

How is gravity simulated?

12.6 Simulated Gravity

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 Questionson 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

Loop on a roller coaster

Car turning around a curve

Centripetal Force: identify the cause of centripetal force

Earth’s Orbit

Revolution of a ball on a string

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.

12.6 Simulated Gravity

http://www.daviddarling.info/encyclopedia/A/artgrav.html

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

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.

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.

12.6 Simulated Gravity

Stanford TorusThe 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/gravity-forces.html