Density Lab B

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Re: Density Lab B

Postby Nba2302 » November 30th, 2018, 2:48 am

I am really confused on hands on task, part 4. I know it uses Archimedes principle, but how are you supposed to know how deep the object will go. I couldn't find it anywhere.

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Re: Density Lab B

Postby knightmoves » November 30th, 2018, 11:19 am

Nba2302 wrote:I am really confused on hands on task, part 4. I know it uses Archimedes principle, but how are you supposed to know how deep the object will go. I couldn't find it anywhere.


You have a solid object (say a block of wood). When you place it in water, it floats partially submerged. What determines how much of the wood is submerged?

You know the buoyant force on the wood is equal to the weight of the water that you displace, which is the volume of wood underwater multiplied by the density of water.

You know that in the steady state, there's no net force on the wood.

So you can calculate where on the wood block the surface of the water ends up.

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Re: Density Lab B

Postby Nba2302 » November 30th, 2018, 2:36 pm

I am on hands on task, part 3 (how much mass a helium balloon can lift). I went to this website-https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/ArchAnswer5.html. I am wondering what the formula for this is and what is the answer in the that nasa example, because i couldn't find how much that balloon in the example could lift

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Re: Density Lab B

Postby John Richardsim » December 1st, 2018, 7:08 pm

Nba2302 wrote:I am on hands on task, part 3 (how much mass a helium balloon can lift). I went to this website-https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/ArchAnswer5.html. I am wondering what the formula for this is and what is the answer in the that nasa example, because i couldn't find how much that balloon in the example could lift

In this case, the maximum weight that can be suspended in the air without moving downwards is equal to the mass of air that is displaced.



Putting this into terms of forces, the force of gravity on the suspended mass equals the force of gravity that would act on the volume of displaced fluid.



The "g" (acceleration due to gravity) in the above equation may be eliminated, leaving:



Therefore, the amount of mass that may be suspended in the air is identical to the mass of the displaced air. Using the equation for mass density, we can rewrite this equation as



This is what was found in part 2 of that link.

Part 3 find the maximum load that may be carried by the balloon by accounting for the mass of the balloon itself and the helium:



Part 4 of that link then translates the mass of the load back into the gravitational force on the load by multiplying the mass by the acceleration due to gravity.
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Re: Density Lab B

Postby Nba2302 » December 1st, 2018, 7:21 pm

I just took the density lab test. It is extremely easy. I was shocked

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Re: Density Lab B

Postby knightmoves » December 9th, 2018, 8:30 pm

UTF-8 U+6211 U+662F wrote:#3 would probably require the density of helium.


You're overthinking this - it's a hands-on task.

Weigh some object on the balance. Tie the balloon to the object and weigh it. Subtract.

Or (probably works with most electronic balances) hold the balance upside down, zero it, then place the balloon under the pan and record reading.

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Re: Density Lab B

Postby OrangeQuail9 » Yesterday, 8:01 pm

Shouldn't Density Lab be a cheat sheet event? There are some formulas but not big complicated ones and it's mostly math so I don't really need that much information.

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Re: Density Lab B

Postby MattChina » Today, 5:17 am

OrangeQuail9 wrote:Shouldn't Density Lab be a cheat sheet event? There are some formulas but not big complicated ones and it's mostly math so I don't really need that much information.

Well, I mean the point of most physics events is that you can put a lot of information, but you have to be able to apply the equations and figure it ouy for yourself. As for density lab, I agree there's not that much information you can put on there, and the formulas are really simple, but I guess it just wouldn't really make a difference. Also i think notesheets are for events more information-based so theres a lot of info to put in a short space and instead of a small amount in a small amount of space
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