The String Tension of a Rotating Rod: Is $\omega \propto M^{-1}$?

In summary, the centrifugal force at the rotating extreme of a rod is proportional to the rest mass and angular speed, and this relationship also applies to strings, where the tension is inversely proportional to the mass.
  • #1
arivero
Gold Member
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Consirer a rod rotating about one of its extremes such that the other extreme rotates at lightspeed. The centrifugal force at this extreme is
[tex]
F \propto M \omega c
[/tex]

where M is the rest mass and w the angular speed. If the rod were a flexible one we should call it a string, it could vibrate around to keep the stress constant, and this stress (the string tension) should be equal to the Force above, so I wonder if the above formula apears also in strings.

If it does, then the string tension imposes a relationship
[tex]
\omega \propto M^{-1}
[/tex]
Does it?
 
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  • #2
Yes, this relationship is true for strings. The tension of a string is inversely proportional to its mass, so that when the mass is increased, the tension decreases, and vice versa. This is why it is possible for a string to vibrate even when one end is rotating at lightspeed - the tension of the string is reduced due to the increased mass, allowing it to vibrate more easily.
 
  • #3


I would approach this question by analyzing the proposed relationship between angular speed (ω) and rest mass (M) in the context of a rotating rod and a vibrating string.

First, it is important to note that the formula F ∝ Mωc represents the centrifugal force at the extreme end of a rotating rod. This means that as the angular speed increases, the centrifugal force also increases, and as the rest mass of the rod increases, the centrifugal force decreases.

Next, the author suggests that if the rod were flexible and could vibrate, the string tension (which is equal to the centrifugal force) would also be equal to the formula F ∝ Mωc. This implies that the string tension would also be affected by changes in angular speed and rest mass.

Based on this information, the author poses the question of whether the relationship ω ∝ M^-1 holds true for strings as well.

In order to answer this question, further analysis and experimentation would be needed. It is possible that the relationship does hold true for strings, as they are also subject to the same forces (centrifugal force and string tension) as the rotating rod. However, it is also possible that the relationship may be different for strings due to their different properties and behavior compared to a rotating rod.

In conclusion, while the proposed relationship between ω and M in the context of a rotating rod and a vibrating string is interesting, more research and experimentation would be needed to definitively determine if the relationship holds true for strings.
 

Related to The String Tension of a Rotating Rod: Is $\omega \propto M^{-1}$?

1. What is the relationship between angular velocity and mass for a rotating rod?

The relationship between angular velocity ($\omega$) and mass ($M$) for a rotating rod is inversely proportional, meaning that as one increases, the other decreases. This can be represented by the equation $\omega \propto M^{-1}$, where $\propto$ indicates proportionality.

2. How does the string tension affect the rotation of the rod?

The string tension plays a crucial role in determining the angular velocity of a rotating rod. When the tension in the string increases, it causes the rod to rotate at a faster rate. This is because the tension is responsible for providing the centripetal force needed for circular motion.

3. Is the relationship between string tension and angular velocity linear?

No, the relationship between string tension and angular velocity is not linear. As mentioned before, it is inversely proportional, which means that the graph of tension vs. angular velocity will be a hyperbola rather than a straight line.

4. Can the relationship between string tension and angular velocity be applied to other rotating objects?

Yes, the relationship between string tension and angular velocity can be applied to any object that is rotating about a fixed axis and connected to a string. As long as the tension in the string is the centripetal force acting on the object, the inverse proportionality will hold.

5. How does the mass of the rotating rod affect its stability?

The mass of the rotating rod does not directly affect its stability. However, the distribution of mass along the rod can impact its stability. A rod with a more concentrated mass towards its center of rotation will be more stable compared to one with a mass that is evenly distributed or concentrated towards the ends.

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