Transcript Artificial Gravity - Northern Illinois University

Artificial Gravity
Central Force

There is no normal or
tension force affecting things
in orbit.

Like falling bodies that
accelerate, a satellite
accelerates toward the earth.

Gravity is a central force.
orbital
velocity
centripetal
acceleration
Satellite
Earth
Force on Mass

Newton’s law of acceleration
applies to orbits.
• Centripetal acceleration times
mass is the force of gravity
F

The situation is the same for
the satellite or any object in
the satellite.
a
Earth
Satellite or
astronaut
Free Fall

The net force of an object in
circular orbit matches the
centripetal acceleration.


This is the same for a freely
falling object.
Velocity does not change the
force or acceleration.
v
Fnet
a
a=g
Fnet = mg
v
Earth
Weightlessness

Objects in free fall exert no normal force.
• Fnet = -ma = -mg + FN
• If a = g, FN = 0

The same is true in orbit.
• Fnet = mar = Fgrav + FN
• If ar = Fgrav/m , FN = 0

Objects in orbit are weightless.
Spin the Station

A spinning station in orbit has
a centripetal acceleration of its
own.
• Acceleration is on the inside
pointing inward.

There is a corresponding
centripetal force for object on
the inside wall.
Satellite
F
a
Station Gravity

The centripetal force is like
an elevator accelerating
upward.
• Fnet = mar = FN
Satellite

The net force must be due to
a normal force.
• Experience as weight
W  mar  mrw 2
• If rw2 = g then it matches
earth’s gravity.
F
a
Centrifuge

A centrifuge spins to create
an artificial gravity.
• Liquid separation
• Pilot training
• Amusement rides
Gravitron

The Gravitron is an
amusement ride that uses
centripetal force.
• Rotates at 24 rpm
• Diameter is 14 m
W  m ar  m rw 2
r  7m
w  (2 )(24rpm)(1 min/60sec)
w  2.5rad/s
rw 2  44m/s2  4.5 g
Centripetal Correction

The spin of the earth creates
a centripetal acceleration
toward the axis of the earth.
a = w2r

The effect is like accelerating
down in an elevator.

Items weigh less at the
equator.