B Conservation of Angular Momentum - Problem understanding this scenario

AI Thread Summary
In a closed system, both linear and angular momentum are conserved, but their conservation can appear counterintuitive in certain scenarios. When two equal mass balls are fired from a stationary disk in opposite directions, the linear momentum remains zero, while the disk begins to spin, indicating a change in angular momentum. The key point is that the angular momentum of the balls must be considered, as they possess angular momentum relative to the center of the disk. This illustrates how linear motion can still contribute to angular momentum when measured from a specific point. Understanding these relationships clarifies the conservation principles in such dynamic systems.
jonhswon
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Hello,

As far I know, in a closed system both, linear and angular monentums, are conserved.

İmagine such a scenario: everything is motionless, both momentums zero initially, then from a disk are fired (compressed spring push) two equal mass balls at same speed but opposite direction. Now balls fly away and disk is spinning. Linear momentum after firing is still zero, but angular momentum is not? What is happening?

(All usual assumptions in place, inertial reference, massless springs, etc..)

Thnaks in advance.

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jonhswon said:
angular momentum is not
Have you taken into account the angular momentum of the balls?
 
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... an object moving in a straight line at constant velocity has angular momentum about any point not on the line of motion.

Note also that angular momentum is always measured relative to some point.
 
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OMG I was so blind. Thanks a lot !
 
I first had this discussion the other way round when a classmate at university lobbed a shoe at the door to shut it. It's quite neat how the changing tangential component of linear velocity cancels with the changing radial distance to produce a constant angular momentum for an object in linear motion.
 
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