Standing Waves: Finding the number of antinodes

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A string with a fixed frequency vibrator forms a standing wave with 4 antinodes at tension T1. Upon increasing the tension to T2, the standing wave re-establishes with a different number of antinodes. Initial thoughts suggested there would be 8 antinodes due to doubling with frequency increase. However, the correct conclusion is that the number of antinodes increases by one, resulting in 5 antinodes at tension T2. Understanding the relationship between tension and antinode count is crucial for solving such problems.
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Homework Statement



A string with a fixed frequency vibrator at one end forms a standing wave with 4 antinodes when under tension T1. When the tension is slowly increased, the standing wave disappears until tension T2 is reached with no resonances occurring between the two tensions. How many antinodes are there in this new standing wave?

Homework Equations


The Attempt at a Solution



There would be 8 antinodes, right? Because as you jump up to the next frequency, the number of antinodes doubles.

Actually, no, it would be 5 antinodes, right?
 
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I believe it would be 5 antinodes. Going from a given resonant tension to the next increases the number of antinodes by one.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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