# Tag Info

11

The data manufacturers provide assume the tyre pressure is adjusted with tyres cold (ambient temperature) prior to loading. Though the small error introduced by making adjustments after loading will not be significant, the difference between cold and hot tyres is greater. Recommended pressure is higher for a 'full laden' car. That is why a spare tyre has to ...

10

Very interesting observation. I think what you are observing when your mouth is away from the tube is MORE than just the air you exhale - because the air in the vicinity of your breath is being "dragged along" by something called "entrainment". This is the principle behind an ingenious fan, called the Dyson Air Multiplier: A detailed explanation of how it ...

10

The relative humidity of air is pressure dependent. Your method of popping your ears involves increasing the pressure of the air in your mouth. And if you sufficiently compress a volume of air that has a high relative humidity, you can increase the air's relative humidity beyond it's saturation limit, which causes the water vapor in the air to start to ...

4

The question Does the pressure inside a tire equal to its average ground pressure? is related. If we can ignore the rigidity of the tyres then the air pressure in the tyres multiplied by the four tyre contact patches must be equal to the car weight, so the pressure would be given by: $$P = \frac{Mg}{A}$$ where $M$ is the car mass and $A$ is the total ...

3

I will attempt to go more in-depth into the physics here. In practice, the unloaded weight of the car is non-zero, but I'll consider two states where the first state refers to zero weight on the tire. In order to make a practical calculation for the car, then, you'll use the numbers for the second state, subtracting one vehicle weight from another. There ...

3

TL;DR: The load does not significantly increase the pressure in the tire, but not inflating the tire more will increase friction. This will heat up the tire. Correct pressure ensures correct contact area - preventing wear on the tire, and keeping rolling friction low. Full answer: Going to use simple math, round numbers (no calculator): 1000 kilo car, 4 ...

3

This phenomenon has been well-researched. If the underground pipe is almost full with rapidly-flowing water the waves in the pipe will cause the pipe to be completely filled in some places. The waves are irregular and the air in between the wave crests gets compressed - when it passes the manhole access the air is vented. 1000Pa is actually a very small ...

2

When the cap bursts off the bottle the air inside it will expand rapidly and adiabatically, so its temperature will fall. If there is enough water vapour in the air inside the bottle, and if the temperature reduction takes the temperature below the dew point, the water vapour will condense giving the fine mist that you see. In this case it looks to me (it's ...

2

The first explanation is correct: tire pressure increases with an increasing load. The second explanation has a problem in that the phrase "the amount of air inside the tire is constant" is being too vague as to what "the amount of air" means. The number of molecules of air inside the tire remains constant. But the volume of air does not remain constant; ...

2

As mentioned in the other answer, additional air is being entrained. This principle can be used to produce considerable flows and considerable pressure differences. Examples In a steam locomotive, the exhaust steam from the cylinders is directed to a nozzle that points upwards towards the exit of the funnel. This draws the smoke through the boiler and ...

2

The jumping manhole lid caused by the Bernoulli`s principle sounds quite reasonable at the first glance. However, I have seen a few storms in my life, but no jumping manhole covers that I can recall. Also, I noticed, that in the video the jumping does not match the wind gusts (observe that small tree). In the absence of trolling sewer workers, the lid ...

1

There's static pressure (P) and dynamic pressure ($\frac{1}{2} \rho v^2$). A pitot tube placed in the center section of your drawing will measure the stagnation pressure, which is the sum of the two terms. Physically, the dynamic pressure will be larger at the narrow section, and the static pressure will be smaller there. The sum will be constant ...

1

Any kind of "funnel" - an area where tall buildings create an obstacle to the free flow of air - acts as an amplifier to wind. That is, even a little bit of air moving from point A to point B will notice the "obstacle" that is a pair of buildings; it will build up pressure in front of the buildings and result in a faster flow of air through the passage. An ...

1

This is actually hinted at in an existing answer (on re-reading) but (and this is a rather handwaving take on the question as we don't have much data on tyre deformation, expanded from an intended comment): There's a further explanation which I believe to be closer to the correct one, as the pressure change shown can be large compared to the mass change, ...

1

I can only assume that 25 cm of vacuum refers to a vacuum which is at 25 cmHg of pressure. I do think going down to 25 cmHg would mean ~33,330 Pa; that's within the range of a low vacuum.

1

The area of the manometer tube makes no difference. All that matters is the difference in the heights of the two ends (labelled $x$ in your diagram). That's why pressure units like the torr exist that are (or rather were) defined as the pressure difference when the difference in height of a mercury manometer is 1mm. All that matters is the height difference. ...

1

Everything depends on the size of the air pocket, since you can treat the water as incompressible. As water is lost, the air pocket expands, lowering the pressure. If the air pocket is large, it takes a lot of water loss to lower the pressure a certain amount. If the air pocket is small, the pressure will be very sensitive to loss of water. Check out ...

1

Assumptions: The hole is in the region below the air pocket (so water, not air, is leaking) Air pocket volume is $V_p$ when the pressure is $P$ Isothermal process (slow expansion: temperature constant) Volume of container doesn't change with pressure (probably not true… - this will underestimate the leakage rate) you can write the rate of change of the ...

1

One could probably measure the light pressure of a photon gas on a pair of parallel mirrors. Experimentally that's on the order of 1e20+ particles in a relatively small setup with two dielectric mirrors and a laser. The resulting force should be around 1e-7N, which is easily measurable. Would you accept that as an implementation, or are you looking for an ...

1

Usually it's not quite true that there is no regulator - typically these types of cylinders have a pressure reduction valve that doesn't look like much. There's nothing to "regulate" but they reduce the pressure from 100+ bar to something that makes sense for filling balloons. A similar thing is used in scuba diving: the "primary regulator" takes the ...

1

For aviation purposes, standard atmosphere is considered to be dry air at mean sea level, at 15 degrees C (59F). It is true that pressure decreases with increasing altitude, and temperature usually does, but not always. It is not a simple relationship, because it depends on humidity, heat transfer from above and below, vertical circulation, horizontal ...

1

Why can't we measure the pressure at 1000 m for different temperatures? Meteorologists certainly can do that, and in fact do do that, all the time. They use weather balloons, sounding rockets, and all other kinds of instrumentation to measure conditions in the atmosphere. The resulting picture is rather complex. Conditions vary with place, the seasons, ...

1

I think there is a difference between the amount of pressure exerted on a flat surface by the fluid in a wind tunnel versus the amount of pressure that makes down your ear canal to your ear drum. The wind in a wind tunnel is not directly incident on your ear drum. I imagine if one could directly apply a 15 m/s flow onto the ear drum, it would hurt. ...

1

Well this happens mainly due to two factors- The pressure difference inside the drain and outside. there is high pressure inside the drain which is balanced by lifting the lid. The excessive increase in water level in the drain. These two factors result in the water gushing out after the air from the air gaps come out. This may also happen due to ...

1

I know that air pressure and temperature are inversely proportional. You should not know that. This is the source of your misunderstanding. The ideal gas law, $PV=nRT$, can be rewritten as $P=\frac R m \rho T$, where $m$ is the average mass of a molecule in the gas and $\rho$ is the density of the gas. The first term on the right is a constant for a ...

1

All first order phase transitions have a change of volume. With different pressures you need to consider the sign of the work $P\Delta V$ that needs to occur during the phase change. If $\Delta V$ is positive, the phase change will occur at a higher temperature for higher pressure. If negative, the phase change will occur at a lower temperature. (Note ...

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