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14

There's two possibilities that are immediately obvious. The first is that the pressure inside the house is slightly lower than the pressure outside the house before you light the fireplace. This would cause air to flow down the chimney into the house which would keep push the flame into the house instead of up the chimney. This would be easily testable if ...


12

You're not getting enough Make-Up Air. I strongly encourage you to install a CO detector in you home and reassess your HVAC situation (especially the 'V' part, ventilation). Lack of sufficient makeup-air in a house with gas fired equipment is dangerous. This is usually more of a problem with new-construction homes that are built to be nearly hermetic. ...


8

Tall buildings are subject to the stack effect. Because the interior is held at a different temperature than outside (due to indoors temperature control), the vertical pressure gradient is different. Typically it is a reasonable assumption that the pressure inside the building is continuous from one floor to the next via the stairwell (if nothing else). ...


4

You need a "draft". When you light the fireplace, initially the heated combustion products want to rise directly up the chimney, but after that occurs for a few seconds it results in a partial vacuum in the house, attempting to suck air back down the chimney. This cause the fire to be blown/pulled outwards into the room. (With a conventional wood-burning ...


3

I will first elaborate what wind-gusts are not, for mental clarification: Thermodynamics as you may have encountered it in a physics course, is a static theory, as opposed to dynamic theories. More specificly that what is taught at university is usually equilibrium thermodynamics - You calculate the equilibrium state of a system where it will end up, but ...


3

Given the imprecision in these numbers, that means that you can lift anywhere between 0 and 0.1 kg per m^3 of air. Per Wikipedia, a typical hot air balloon holds 2,800 m^3 of air in the envelope, so it can suspend something between 0 and 280 kg in the basket. A typical human weighs under 100kg, so you could probably lift between one and three people with a ...


3

There seems to be a slightly lowered pressure inside the room the fireplace is in, which leads to air actually streaming down the chimney to equalize it, and this blows the flames into the room. When you open the door, you allow air draught to stream into the room and up the chimney, as it is supposed to, and that sucks the flames into the chimney. ...


3

Yes. Air has mass, and anything with mass has inertia. Due to these inertial effects, the air in a car will be redistributed as you would expect any other object with mass to move in a non-inertial frame. See Why does a helium filled ballon move forward in a car when the car is accelerating?


3

By the equivalence principle you can take into considerations the effects of gravity on pressure for instance. Then it is known that pressure depends on altitude (although this dependence is not simple due to many other factors). The general relation for the pressure gradient is $$\nabla p=\rho\mathbf g$$ where $\mathbf g$ is the gravitational acceleration, ...


3

This is really a comment to the two existing answers from Phoenix87 and Pranav. I agree entirely with their comments on acceleration. However if the car is not air tight, i.e. if air can flow in and out of the car, then there will be an effect of velocity as well. For example if there are small apertures in the car we'd expect the pressure inside to fall ...


3

Why do we boil water to cook food? It's not actually because there's anything magic about the boiling of water, or that the physical process of boiling in particular does anything. Usually it's because we want a constant-temperature heat bath. Say you are boiling vegetables. You boil water, and you know that water is at 100 degrees. Water actually cannot get ...


2

IF all of the water above the leak point has indeed completely drained away, and the water is completely stationary throughout the pipe's entire length (those are important "if"s), then your problem is quite straightforward! With the density of water, we can easily come up with a direct relation between water height (regardless of the horizontal path taken ...


2

When you reduce the pressure in a vessel by pumping air out you reduce the temperature of the air. If the temperature falls below the dew point then water will condense out of the air and a mist will form. The trouble is that the dew point depends on the pressure, and it falls as the pressure reduces. So whether a mist forms or not is dependant of how close ...


2

The air in the room must be sufficiently laden (ideally, saturated) with water vapor (or another substance, such as alcohol, that can be absorbed by the air). Then, if you drop the pressure suddenly, so that the air can expand adiabatically, the temperature can drop below the dew point of the vapor, and the vapor has an opportunity to condense into a cloud. ...


2

I thnk the answer to this lies in 'Chaos Theory', which can also be described as non-linear dynamics. To give an example of a simple linear system - if you want to travel from the West Coast of the USA to the East Coast of the USA by car travelling at an average speed of 60 miles per hour for 12 hours driving a day you can make a prediction of how long the ...


1

So I found the answer....I was not taking the final step of multiplying The difference in density between the surrounding air and the heated air and then multiplying by the envelope volume. I was just focusing on the difference and getting stuck there. I chose Denver because it's a mile above sea level with a known air density. I could have chosen Mt Everest ...


1

There's no uniform density of heated air. It depends on the temperature (higher T -> lower density) but also on the ambient air pressure. In Denver, cold air is less dense, because the ambient pressure is lower. But this same effect also increases the density of hot air, by the same percentage. So, the result is that the lift of a balloon decreases with ...


1

If we consider temperature to be due to translational motion of the molecules and we assume the system has reached equilibrium, then the velocity distribution of the molecules is given by the Maxwell distribution: $$ f(v) = \sqrt{\left(\frac{m}{2\pi k T}\right)^3} 4 \pi v^2 \exp\left(\frac{m v^2}{2 k T}\right)$$ which will give you the velocity ...


1

In an ideal fluid, assuming the diameter of the pipe after the contraction is the same as the diameter of the pipe before the contraction, $P_2^\prime = P_2$. There is no effect of the contraction downstream from the contraction itself. If we consider an inviscid, isentropic, incompressible flow, the total pressure in the flow is constant along streamlines ...


1

It works because the plastic bottles are filled with water and water is almost incompressible. When subjected to high pressure, the volume inside the bottle stays almost the same (there is a small air bubble that will be compressed), thus the bottle is not crushed. I believe that a plastic bag would work just as well. The hydrostatic pressure is uniform so ...


1

This is a typical problem when starting up a fireplace, wood stove, or what-have-you. The air pressure inside your house at 75 degrees is lower than the outside air pressure at 40 degrees because warm air is less dense than cold air. Result? The higher-pressure air outside the house wants to flow down the chimney and into the lower-pressure area inside your ...


1

Based on your responses to the previous answers, I understand that there are actually two distinct bodies of gas involved in the setup you describe: The gas which, at the start of your experiment, is already in the sample chamber (gas A) The gas which, at the start of your experiment, is stored in a separate vessel at a higher pressure (gas B) These two ...


1

To fluid dynamicists, Bernoulli's equation is better known as the 'Energy Equation' since it does indeed account for the energy changes that occur along a fluid path. The energy equation says that the energy is constant along any given streamline. Static or stagnation pressure can exist in the absence of fluid velocity creating a potential energy component. ...


1

Both cases are true. Basically the force the object will feel is due to the net differences in pressure and viscous forces acting on its upstream and downstream faces. How the pressure field and viscous stress are distributed around the object is as function of a number of factors: the shape of the object, its size relative to the pipe, the wall roughness, ...


1

Yes, $F_b \approx 2 F_a$. The force needed to advance the screw into the water is $F = PA$ where $P$ is the pressure on the end of the screw and $A$ is the cross-sectional area of the screw. When the height of the water is doubled, the pressure is also doubled. The relation is not exact because your scenario doubles the height of the water from the bottom ...


1

Under common assumptions and ignoring potential energy, static pressure is the expression of the fluid's temperature (internal energy) and dynamic pressure is the expression off the fluid's velocity, so if the fluid is brought to a rest adiabatically, their sum is equal to the stagnation pressure. The stagnation pressure represents the total energy of the ...



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