Density Lab B

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Re: Density Lab B

Postby UTF-8 U+6211 U+662F » November 15th, 2018, 3:28 pm

Nba2302 wrote:Are there any archived/past tests for this event? So far I cant find them :cry:

This event is new. There is a test on the test exchange from the summer, but be aware that parts might be updated.

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Re: Density Lab B

Postby MattChina » November 15th, 2018, 5:59 pm

Nba2302 wrote:Are there any archived/past tests for this event? So far I cant find them :cry:

theres a one on the text exchange from the SSSS
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Re: Density Lab B

Postby Anomaly » November 15th, 2018, 6:35 pm

Nba2302 wrote:Are there any archived/past tests for this event? So far I cant find them :cry:

If you look on the old test exchange under the 2018 season full sets, there's a garnet valley test set there, which includes the Density Lab test they had when they ran it as a trial (tbh though that one is super basic)
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Re: Density Lab B

Postby Nba2302 » November 17th, 2018, 9:41 am

Can anyone help me on finding the density of gas pls? I look at all the websites, but I don't get it

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Re: Density Lab B

Postby UTF-8 U+6211 U+662F » November 17th, 2018, 3:27 pm

Nba2302 wrote:Can anyone help me on finding the density of gas pls? I look at all the websites, but I don't get it

The density of the gas depends on the pressure, the temperature, and the volume of the gas. Could you be a little more specific about what information you want to find the density of a gas from?

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Re: Density Lab B

Postby Nba2302 » November 17th, 2018, 5:44 pm

Understanding PV=nRT

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Re: Density Lab B

Postby UTF-8 U+6211 U+662F » November 17th, 2018, 6:35 pm

Nba2302 wrote:Understanding PV=nRT

The pressure of a gas is inversely proportional to the volume when the temperature is held constant. This is called Boyle's Law. This make sense because when you press a gas with more force, it shrinks, and the volume decreases.

When the pressure is held constant, the volume is directly proportional to the temperature. This is called Charles's Law. When a gas gets hotter, the particles in it start moving faster, so the gas gets bigger.

When the volume is held constant, the pressure is directly proportional to the temperature. This is called Gay-Lussac's Law. When the particles in the gas get faster, they start exerting more force, so it makes sense that an increase in pressure results in an increase in temperature.

Combining all three of these laws together gives PV = some constant * T.

There's one more thing that we have to take into consideration, which is the number of particles of the gas. More particles, more force, more volume, and less average energy. Since gases have so many particles, we count the number of particles in moles, similar to how we count eggs in dozens. A mole is 602214076000000000000000 particles (Avogadro's number). So, we multiply by the number of particles.

PV = n * some other constant * T.

R is the ideal gas constant. It turns out that all gases have the same volume under the same pressure-temperature conditions! This is Avogadro's law. That means that R is the same thing for all ideal gases. In the end, we have PV = nRT.

In SI base units, pressure is measured in pascals, volume is measured in cubic meters, amount of particles is measured in moles, temperature is measured in kelvins/degrees Celsius, and the units of the ideal gas constant work out to be (pascals * cubic meters)/(moles * kelvins).

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Re: Density Lab B

Postby Nba2302 » November 20th, 2018, 8:20 am

What are the best websites for this event(besides Density Wiki page)? Any links?

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Re: Density Lab B

Postby Galahad » November 20th, 2018, 4:21 pm

Nba2302 wrote:What are the best websites for this event(besides Density Wiki page)? Any links?


NASA has some pretty good practice problems, and ChemIX has every periodic table number you'll ever need.

Other than that, everything else is from obscure websites.

Khan Academy and Physics Classroom explains stuff pretty well, and shows you how to do certain calcs.
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Re: Density Lab B

Postby Nba2302 » November 21st, 2018, 9:41 am

Can anyone help me? Im stuck on Part 2, hands on task. Number 3(the helium balloon) and number 4 ( depth of which object will sink). Are there any links, that will tell me how, or explain?

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Re: Density Lab B

Postby someone1580 » November 21st, 2018, 10:12 am

Nba2302 wrote:Can anyone help me? Im stuck on Part 2, hands on task. Number 3(the helium balloon) and number 4 ( depth of which object will sink). Are there any links, that will tell me how, or explain?


For number 4 I believe we can use specific gravity to figure out whether the object will sink or float. Then using the Archimedes principle and buoyant force we can calculate how deep the object will sink. Search it up :)

For number 3 hopefully this link can get you an idea:https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/ArchAnswer5.html

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Re: Density Lab B

Postby Nba2302 » November 29th, 2018, 1:49 pm

2 days left until my meet. I only have 7 pages of notes. What should I do? It feels like I covered everything

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Re: Density Lab B

Postby MattChina » November 29th, 2018, 3:04 pm

Nba2302 wrote:2 days left until my meet. I only have 7 pages of notes. What should I do? It feels like I covered everything


I feel like 7 notes is sufficient for this event, I mean theres not much to cover.
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Re: Density Lab B

Postby Nba2302 » November 29th, 2018, 5:45 pm

I feel like I am overdoing the hands on task, part 3 and 4(the helium balloon and the depth it will sink). It took half a page(and bunch of formulas) just to find out how much the balloon can lift, same with part 4. Am i doing it wrong?

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Re: Density Lab B

Postby UTF-8 U+6211 U+662F » November 29th, 2018, 6:24 pm

Nba2302 wrote:I feel like I am overdoing the hands on task, part 3 and 4(the helium balloon and the depth it will sink). It took half a page(and bunch of formulas) just to find out how much the balloon can lift, same with part 4. Am i doing it wrong?

Use Archimedes' principle: "Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces"

In both problems, the buoyant force must cancel out the downward force of weight.

#3 would probably require the density of helium.
For #4, I would assume the object has a constant density. That means we could use the weight of the object and the density of water to find the volume of the object submerged. Then, finding the height should be simple if the object is an easy shape like a cube.


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