Conservation of angular momentum

In summary: Friction is the force that resists motion between two surfaces in contact. In this case, it is friction between the block and the disc that allows the block to start rotating when it is dropped onto the disc. Friction creates a torque on the block, causing it to start rotating with the disc. In summary, friction is the force that makes the block start rotating when it is dropped onto a rotating disc.
  • #1
Leong
382
2

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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  • #2
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.
 
The questions are

What is conservation of angular momentum and why is it important?

The conservation of angular momentum is a fundamental principle in physics that states that the total angular momentum of a system remains constant in the absence of external torques. In simpler terms, it means that the spinning motion of an object will remain constant unless acted upon by an external force. This concept is important because it helps us understand and predict the behavior of rotating objects, such as planets, stars, and even subatomic particles.

How is angular momentum conserved?

Angular momentum is conserved through the principle of inertia, which states that an object will maintain its state of motion unless acted upon by an external force. In the case of angular momentum, this means that an object will continue to spin at a constant rate unless an external torque is applied to change its rotation.

What is the role of angular momentum in orbital motion?

In orbital motion, angular momentum plays a crucial role in maintaining the stability of the orbit. In the absence of external torques, the angular momentum of a planet or satellite will remain constant, keeping it in a stable orbit around a central body. This is why planets and satellites do not spiral into their central bodies, but instead maintain a constant distance.

How is angular momentum related to the Law of Conservation of Energy?

Angular momentum and the Law of Conservation of Energy are closely related. Both principles state that the total amount of a physical quantity remains constant in a closed system. In the case of angular momentum, this quantity is the rotational motion of an object, while in the Law of Conservation of Energy, it is the total energy of a system. Therefore, the conservation of angular momentum is a consequence of the Law of Conservation of Energy.

What are some real-life examples of conservation of angular momentum?

There are many examples of conservation of angular momentum in our daily lives. For instance, when a figure skater pulls in their arms during a spin, their rotational speed increases due to the conservation of angular momentum. Another example is the stability of a bicycle, which is maintained by the spinning wheels and the conservation of angular momentum. Additionally, the rotation of planets and galaxies is also a result of the conservation of angular momentum.

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