# Tension and Buoyancy

Hello, if I were to suspend a rubber stopper into a graduated cylinder filled with water, with the stopper half in the h2o and half out of it, how would i calculate the tension in the string? Experimentally, i would collect the displaced volume, density (1000kg/m3), and mass of stopper. I am only in AP physics B, so i cannot use an extremely intense formula. I know buoyant force is rho x volume x gravity and weight is mass x gravity obviously. Any help on this soon would be great. Thank you!

## Answers and Replies

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SteamKing
Staff Emeritus
Homework Helper
What forces are acting on the rubber stopper? What is causing the tension in the string in the first place?

Chestermiller
Mentor
Have you been taught to use free body diagrams? If so, you should have no trouble answering SteamKing's question.

Yes I know how to use fbds, however only half of the rubber stopper is in the water. It is not submerged. For the submerged experiment, I would do T equals W minus Force buoyancy. But when only half of the stopper is in the water (and it is not floating, it's being suspended by the string), how would this equation change? Thank you

Pythagorean
Gold Member
Archimedes Principle

Chestermiller
Mentor
Yes I know how to use fbds, however only half of the rubber stopper is in the water. It is not submerged. For the submerged experiment, I would do T equals W minus Force buoyancy. But when only half of the stopper is in the water (and it is not floating, it's being suspended by the string), how would this equation change? Thank you
If it's only half-submerged, that only affects the magnitude of the buoyant force on the stopper. It doesn't affect qualitatively the free body diagram or the identification of the forces acting on the stopper.

Thank you very much for answering. How would the magnitude be affected? Would the buoyant force be in half? Or something of that nature.. Thanks

Chestermiller
Mentor
Thank you very much for answering. How would the magnitude be affected? Would the buoyant force be in half? Or something of that nature.. Thanks
Can you articulate Archimedes Principle? If you can state the principle, you should have no trouble determining the buoyant force.

Oh yes, I was overthinking it. Thank you all for the help