Class Notes (784,511)
Canada (481,194)
Science (61)
SCI 206 (14)
Lecture 3

week 3.docx

4 Pages
135 Views
Unlock Document

School
University of Waterloo
Department
Science
Course
SCI 206
Professor
Stefan Idziak
Semester
Fall

Description
Pressure 1 Ideal Gas Law: Pressure, Density, Temperature, etc.  Discuss the structural differences between a solid and a liquid. o A solid is structural and arranged in a periodic manner, such that if we know the location of one molecule, we can infer the location of all other molecules in that structure o Conversely, the molecules in gas are much farther apart from each other, and there is no defined structure  What happened when we ran an air hose through liquid nitrogen? Why? o We caused some of the gases in the air to condense into liquids, while some others remained as gas o The result was that a combination of gas and liquid came out the other end o This is a property of gases - at certain temperatures, the molecules come together close enough that the substance takes on the consistency of a liquid  Explain how the concept of pressure applies to a gas. o Recall that pressure = force / area o And the individual molecules in some sample of gas push against the walls of their container, and create pressure  Explain how a steam engine works. o It's all about this pressure principle - you evaporate water and now we have lots of steam in a confined space o Thus it will create pressure against the walls, and this pressure can be used to crank an engine  Why does a balloon make a loud sound when it pops? o It is because there is a sudden release of pressure from the gas molecules which were previously inside, pushing out against the fabric of the balloon  When this pressure is suddenly released, a loud sound is made o Note that the pressure inside is (definitely) greater than the pressure outside because the pressure inside needs to keep the balloon stretched out  Explain gaseous temperature on a molecular level. o Temperature of some sample of gas is related to how quickly the molecules of gas are moving around o Note that if they move around faster, they will bump into the walls with more force and thus create greater pressure as well - that's why if a gas is in a container than can expand, heating the gas will cause the container to expand  How do we apply the molecular explanation of temperature to making bombs and popcorn? o Both things involve the principle of heating something up so that it expands so much and so rapidly that an "explosion" is caused  Either the bursting of the kernel into a piece of popcorn  Or the bomb exploding  Explain gaseous density on a molecular level. o Density is just how many gas molecules there are in a given area o Again, when the density is higher, the pressure will be higher because more gas molecules will be hitting the sides of the container  How does this apply to using a straw? o We are basically sucking the air out of the straw, meaning that there is less pressure available to push the liquid down o Thus liquid is able to come up the straw and into our mouth :) Pressure 2  What does the Ideal Gas Law tell us? o PV = nRT, or P = number density x R x T o Pressure is proportional to density of particles times temperature Atmospheric Pressure and Buoyancy  Explain the "box" model of atmospheric pressure. o If we are talking about the atmospheric pressure acting on a single person, imagine that the column of air above him is divided into boxes o Gravity acts (as it always does) on these boxes, and so there is a downward force on the person created by all this air  However, there are also air boxes which push up to counteract this (that is why we are not crushed) o As we get higher on this "pile" of boxes, there is more air pushing up and less air pushing down, so the air pressure we experience is less  Why was it hard to pull those rubber disks apart when the air was removed from inside them? o Because removing the air meant that the air pressure in the "container" was reduced to zero, all the air from outside wanted to get in so that pressure could equilibrate o This air created a force which opposed the efforts to pull the discs apart  Why does it not hurt to lie on a bed of nails? o Because the pain which we traditionally think nails cause is due to pressure, which (recall) is related to force and area o In this case, we are spreading out the area of the pressure source by putting many nails, and thus the total pressure is not too bad  What would happen if the cabin of an airplane became de-pressurized, and I failed to put on my oxygen mask? o All the intestinal gas we have (which is now kept at a certain density because of the atmospheric pressure from outside) would now be subjected to less atmospheric pressure, and so it would expand (very uncomfortable!)  What is Archimedes' Principle of Buoyancy?
More Less

Related notes for SCI 206

Log In


OR

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.

Submit