Archimedes Squeeze Experiment - Density values over 1g/cm3 not sinking?

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DDore140
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Archimedes Squeeze Experiment - Density values over 1g/cm3 not sinking?

Post by DDore140 »

Hi there

Question re Archimedes Squeeze experiment https://www.sciencebuddies.org/science- ... -boat-sink which my daughter tried at home.

When she did the experiment, the foil ball with a diameter of 2.8cm sank, with the longer diameters ranging on average from 10% submerged for 6cm, to 64% submerged for 4cm diameter to 90% submerged for 3cm. That all seems very explainable with regards to the % submerged increasing as the diameter decreased, and the resulting volume decreased and the corresponding density increased.

The query relates to the actual density values calculated based on the reducing diameter measurements. The density values where nearly all greater than 1g/cm3, the density of water. eg 4.5cm diameter had a density of 1.13g/cm3, 3.5cm equated to 1.46g/cm3 and the 3cm equated to 1.70g/cm3 - yet none of these balls sank but ranged in % submerged from 40% to 90%. The 2.8cm diameter sphere sank with a density of 1.82g/cm3. She expected that the spheres with a density greater than water would sink? Is partial submerging expected with densities greater than water? What explains the tipping point of the ball sinking when the density value reached earlier in the experiment was already greater than that of water. As the experiment is limited with regards to approximate diameter values as balls were not uniformly uniform, she understands values are not fully accurate. She (and I) just want to understand more what is going on to explain to actual experimental results. Overall, the experiment demonstrates well how increasing density decreases buoyancy. Is the presence of air captured in the ball a contributing factor to how quickly the ball sinks, and impacts the actual calculated density of each of the balls/spheres? Are there other factors at play?

Hope the above is clear and really appreciate any thoughts/explanations.

Many thanks
bfinio
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Re: Archimedes Squeeze Experiment - Density values over 1g/cm3 not sinking?

Post by bfinio »

Hi,

Yes, air bubbles trapped inside the aluminum will have a huge impact on its actual density. I assume you are calculating the density using the formula density = mass/volume, where mass is the mass of the aluminum ball (for example measured on a kitchen scale), and volume is the volume of a sphere (according to the measured diameter of the ball). The density you get from that equation would only be accurate if you had a true solid sphere of aluminum. In reality you have a sheet of foil that was crumpled into an approximate ball, and there will be air pockets trapped inside, especially for the larger-diameter balls where you haven't really squished it down yet. So the density values you calculate will not be accurate.

Point being, this experiment works to demonstrate the general trend, but not to compare the exact density of the balls to that of water. You COULD do that with various other solid objects though, by measuring their mass and their volume (which you can do using the displacement method if they have irregular shapes).

Hope that helps!

Ben
DDore140
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Joined: Mon Mar 21, 2022 1:45 am
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Re: Archimedes Squeeze Experiment - Density values over 1g/cm3 not sinking?

Post by DDore140 »

Thanks a million Ben.

That's what we thought but just wanted to make sure our interpretation was correct. As you say experiment is great to show general trend associated with increasing density, but actual density values calculated using sphere volume formula are good to show, but not necessarily accurate. At least my daughter can explain the project limitations in the knowledge that her interpretation is correct.

Many thanks again
Diane
bfinio
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Re: Archimedes Squeeze Experiment - Density values over 1g/cm3 not sinking?

Post by bfinio »

Happy to help! And yes, in general (if your daughter is entering a science fair) I think it's better to be able to explain the results, including sources of error and what you could do differently to correct them, than to have a "perfect" experiment.
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