Conservation of angular momentum

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SUMMARY

The discussion centers on the conservation of angular momentum when a block is dropped onto a rotating disc. It concludes that both the block and the disc will rotate together at a new angular velocity that is slower than the original. The force responsible for initiating the block's rotational motion is identified as friction, which is essential for the transfer of motion between the block and the disc. The experiment described involves using a pulley system to demonstrate how torque is generated through the weight of a bob, ultimately affecting the angular momentum of the system.

PREREQUISITES
  • Understanding of angular momentum and its conservation principles
  • Basic knowledge of friction and its role in motion
  • Familiarity with torque and its calculation
  • Experience with simple mechanical systems, such as pulleys
NEXT STEPS
  • Study the principles of angular momentum conservation in rotating systems
  • Learn about the role of friction in initiating motion and its effects on different surfaces
  • Explore torque calculations and their applications in mechanical systems
  • Investigate experimental setups for demonstrating rotational dynamics, including pulley systems
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and rotational dynamics, as well as educators looking for practical demonstrations of angular momentum concepts.

Leong
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Homework Statement


When a block is dropped to a disc that is rotating with a constant angular velocity about its centre, at the end, we know that both of them will rotate with the same new angular velocity which is slower than the previous one.
Question: What is the force that makes the block to start rotating?


Homework Equations





The Attempt at a Solution



Is it friction? Can friction actually starts a motion of an object? I know that it is friction that slows down the disc but what force makes the object to start its rotational motion? I don't know.
 
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Leong said:

Homework Statement


When a block is dropped to a disc that is rotating with a constant angular velocity about its centre, at the end, we know that both of them will rotate with the same new angular velocity which is slower than the previous one.
Question: What is the force that makes the block to start rotating?
Assemble the disc on a table and create a little pulley on the edge of the table. Tie a bob of some mass around some string and arrange this over the pulley. Then wrap the other end of the string around the axle of the disc. When the string unwinds, the bob will descend to the floor and it's weight will create a downward force, [itex]F[/itex], at some distance [itex]r[/itex], thus creating a torque, which turns the disc.

Is it friction? Can friction actually starts a motion of an object?.
If it weren't for friction, we wouldn't be able to walk.
 

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