Watch the video here httpwwwyoutubecomwatchvGutiNPwzUA8 Then

Watch the video here: http://www.youtube.com/watch?v=GutiNPwzUA8. Then, making relevant assumptions and approximations predict/estimate the density of sulfur hexafluoride, using the fact that the aluminum boat floats. Please clearly list and explain your assumptions, methods for estimating quantities, and cite your sources. Do not simply use the fact that the guy says that the density is approximately 5 times that of air; you are to demonstrate your ability from Fluid Mechanics! Compare your estimate to a literature value. If they do not agree, suggest why.

Solution

The following assertions can be made from the video:

Since the aquarium is filled with SF6, it implies that it has a greater mass compared to air or else it would float on air just as oil floats on water . This implies density of SF6 is greater than air as density is the ratio between mass and volume.

Secondly, when the aluminium boat is placed in the gas filled aquarium, we can observe that it floats over the gas.This implies that mass of SF6 is also greater than that of aluminium since the boat is made of aluminium foil. As a result, density of SF6 is greater than that of Al.

Sources like wikipedia suggest that density of air is 1.225 kg/m3, density of aluminium is 2.70 kg/m3 and density of SF6 is 6.17 kg/m3. Hence, the guy in the video says that SF6 has an approximate density of 5 times that of air.

By applying fluid mechanics, when the boat floats, there is a force of buoyancy acting on the vessel which makes it to float on the gas. Since, the upper surface of the boat is exposed to air and lower surface floats on SF6, there tends to be a pressure difference between both the top and bottom ends due to which buoyancy force acts upwards. As, the boat is filled with SF6 gradually, the pressure difference was reduced and gradually made zero. This is the reason why the boat was later sinked in SF6.

Also, when taken into lungs, the voice seemed to be deep . This is because sound travels slower in a denser medium than a thinner medium. Hence, this again proves SF6 has higher density compared to air.

The floating of air bubbles also suugest that they couldn\'t penetrate through a denser medium like SF6 like they did through air. This adds to the fact that SF6 has density higher than air and experimental observations and mentioned sources suggest their figurative values.