Insect-ring system, conservation of angular momentum

In summary, the circular ring with a small insect on its periphery is placed upon a smooth horizontal surface. The insect starts moving with a velocity v w.r.t ground along the periphery. The angular velocity of the ring is (note*).
  • #1
Krushnaraj Pandya
Gold Member
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Homework Statement


A circular ring (2m, R) with a small insect of mass m on its periphery, is placed upon smooth horizontal surface (axis of rotation passing through center and perpendicular to the ground i.e disk is lying horizontally)
. The insect starts moving with velocity v w.r.t ground along the periphery. The angular velocity of rotation of ring is (note*-I just have a problem with one step of the solution)

Homework Equations


net torque=dL/dt

The Attempt at a Solution


I got the correct answer as v/2r by conserving angular momentum about O (center of disk). What I don't understand is how the net torque about it is zero- surely, the insect must have had to give an impulse to rotate the disc at w from rest, even if for a short time
 
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  • #2
Krushnaraj Pandya said:
What I don't understand is how the net torque about it is zero- surely, the insect must have had to give an impulse to rotate the disc at w from rest, even if for a short time
You are correct. Note that the angular momentum of the system is conserved, not the angular momentum of the disc alone.
 
  • #3
Doc Al said:
You are correct. Note that the angular momentum of the system is conserved, not the angular momentum of the disc alone.
I get that all the forces are internal- but we can't say the disk will apply an equal and opposite 'torque' on the insect can we? then how can we say the net torque is zero
 
  • #4
Krushnaraj Pandya said:
but we can't say the disk will apply an equal and opposite 'torque' on the insect can we?
Why not? Note that the torque is about the axis of the disk. (Just like a point mass can have angular momentum about some point, forces exerted on it may produce a torque on it.)
 
  • #5
Doc Al said:
Why not? Note that the torque is about the axis of the disk. (Just like a point mass can have angular momentum about some point, forces exerted on it may produce a torque on it.)
from what I understand, you're trying to say the reaction force of the disk on the insect exerts the equal and opposite torque about the central axis, am I right?
 
  • #6
Krushnaraj Pandya said:
from what I understand, you're trying to say the reaction force of the disk on the insect exerts the equal and opposite torque about the central axis, am I right?
Right. Thus the net torque on the system is zero and angular momentum is conserved.
 
  • #7
Doc Al said:
Right. Thus the net torque on the system is zero and angular momentum is conserved.
Oh! I get it now, I had confusions about how systems and torques related here...but it's all clear now. Thanks a lot!
 

Related to Insect-ring system, conservation of angular momentum

1. What is an insect-ring system and how does it relate to conservation of angular momentum?

An insect-ring system refers to the behavior of certain insects, such as flies and bees, where they rotate their wings in opposite directions to create a stable flight pattern. This rotation creates a gyroscopic effect, which helps the insects to maintain their balance and conserve angular momentum.

2. Why is conservation of angular momentum important in insects?

Conservation of angular momentum is important for insects because it helps them to maintain stability and control during flight. It also allows them to make quick and precise movements, which is essential for survival in their environment.

3. How do insects use their wings to conserve angular momentum?

Insects use their wings to create a rotating motion, with each wing moving in the opposite direction. This motion creates a gyroscopic effect, which helps to conserve angular momentum. This allows the insects to make quick and precise movements in flight.

4. Are there any other animals or organisms that use a similar system for conservation of angular momentum?

Yes, birds and bats also use a similar system of wing rotation for conservation of angular momentum during flight. This is known as the "clap and fling" mechanism, where the wings create a rotating motion to generate lift and stability.

5. How does understanding insect-ring systems and conservation of angular momentum benefit scientific research?

Studying insect-ring systems and conservation of angular momentum can provide insights into the mechanics of flight and movement. This knowledge can be applied to the development of new technologies, such as drones and aircraft, as well as advancements in biomechanics and robotics.

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