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  • FOSSUM: Hi. My name's Mike Fossum.

  • I'm the commander of Expedition 29.

  • Welcome to the International Space Station.

  • You may wonder why the International Space Station

  • doesn't tumble in its orbit around the Earth.

  • Well, we have a system that maintains our attitude --

  • our attitude control system, if you will.

  • There's really two ways to do this, to approach it.

  • The first way would be to use rockets or small jets

  • that would keep thrusting and pushing

  • to nudge the Space Station into its correct attitude.

  • Problem with using thrusters like that

  • is it requires a lot of fuel

  • that we have to continually ship up from the Earth.

  • So, instead, we use angular momentum and gyroscopes.

  • Let me demonstrate a little bit.

  • Before we get into this,

  • we really have to talk about the definitions of the concepts.

  • It's really the conservation of angular momentum

  • that's really important here.

  • I have this flashlight rotating.

  • In physics, this angular momentum of an object

  • rotating about some reference point

  • right here in the middle --

  • that's a measure of the extent

  • to which the object will continue to rotate

  • around that point,

  • unless it's acted on by an external torque.

  • Now, torque has to do with the ability of a force

  • to rotate an object

  • and how far away from the center that force is applied.

  • The angular momentum of a single, rotating body

  • is equal to the product of its rotational inertia --

  • that's just physical properties of the mass distribution,

  • the rotational inertia --

  • and angular speed, how fast is it moving.

  • The angular momentum and rotational inertia --

  • that includes the mass -- are constants in the system.

  • Angular momentum of the system remains constant

  • if no external force is acting on the system.

  • This is the law of conservation of angular momentum.

  • I can demonstrate this to you

  • with me actually doing a little bit of a demonstration here,

  • so I want you to watch this.

  • I'm gonna have to unclip the microphone,

  • or I'll tie myself up in knots.

  • Again, what's going on as my body spins doing this

  • and moving my arms in and out from being close to the body

  • is when I bring the arms in closer to the body,

  • the body's rotational inertia is decreased.

  • The angular momentum must be conserved.

  • As the rotational inertia is decreased,

  • the angular speed increases and vice versa.

  • This is called an inverse relationship.

  • Now, no external force acts on the system,

  • and thus the angular momentum about the axis

  • must remain the same.

FOSSUM: Hi. My name's Mike Fossum.

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B2 US angular angular momentum momentum rotational inertia space station

Angular Momentum

  • 39 2
    Wayne Lin posted on 2015/02/15
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