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Driving through standing water takes a lot of energy and wants to slow the car down, so to maintain same speed as on a dry surface, you require more fuel, i.e. your mpg will drop. I have instant reading mpg on my BMW 335D and have noticed what would other wise be 30mpg on dry surface can drop to 25 or loess on wet surface. I'm talk surfaces with pooling ...


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That is called EMC : Electromagnetic compatibility. Your DC machine stator is fed through a brush. Since it is rubbing the commutator plates, it can generate sparks, small arcs and so on. Since these phenomena are really fast, they tend to emit electromagnetic radiations in the whole frequency spectrum (see the Fourier transform of a dirac delta function) ...


0

Let's get one thing out of the way: The work done against gravity is the same whether you are running on an inclined treadmill or running (at the same velocity) up a hill. You see this by considering the motion in the frame of reference of the runner - you can't tell whether you are moving up or the hill is moving down. Yet the treadmill is easier for two ...


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I think the most significant difference between work done on an inclined treadmill and work done on a real incline is the gain in potential energy on the real incline. There is no real delta mgz on a treadmill, whereas if you fell back to your starting height from a real incline, you'd certainly notice a large amount of stored energy being turned into ...


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The water inside is a fluid, so it isn't rigidly attached to the walls of the bottle. This means that the bulk of the water will still accelerate at $g$, save for the part of the water close to the bottle walls, which will be dragged along with the bottle. The water isn't really rising up, it's just falling slower than the bottle. In the frame of the ...


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In simple words, you cant hear the person outside shouting because the sound waves generated by the noises in close proximity to you are more dominant and so you tend to hear them more.Also, they hear you clearly because of the assumed lack of noise outside the door.


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It all boils down to energy and heat capacity. Water has a specific heat of 4.186 J/g degreesC, versus air, which has a specific heat of 1.005 J/g degreesC. To keep a radiator at a temperature designed to heat a room, 70C or more, it would take a multiple amount of air blown through, as not only the specific heat per gram but also the density of air ...


2

Simple answer: When you blow harder, more surrounding air gets mixed in with the stream of air from your mouth. The faster air moves, the lower pressure it has (Bernoulli's principle). So when you blow faster, your stream of air is lower pressure than the surrounding air. Thus the surrounding air fills in the stream. The surrounding air is obviously cooler ...


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That may depend on what you call "invisible". How about a system of direction-sensitive Lytro cameras all around a body and projectors transmitting whatever the cameras on the other side of the body sees in the direction opposite to the sensed one? As of today it's a mildly challenging but doable engineering project. Would such a system count?


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A few simple observations will clarify what you see. If the lines are mostly vertical, the are not caused by your eyelashes (which would create a horizontal diffraction pattern). Vertical lines might be caused by diffraction if you can close your eye almost completely - the width of the aperture has to be a few wavelengths at most to see any diffraction ...


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I believe that a simple drawing can clarify some of the misconceptions. In dynamics, you must analize the forces acting on the individual objects separately. I have drawn the forces on the train and on the person: You can see that if the person is not moving the floor must do a force equal to the tension. The internal forces inside the person do not ...


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When water leaves the bottle, the pressure above it drops. This reduces the net force pushing the water out of the opening, until it stops and a bubble can rise up. When the bubble has left the mouth of the bottle, the water can start flowing again. The stop-start of the water, and the reduced pressure inside the bottle, contribute to the lower flow rate in ...


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Assuming you start with a full bottle of water, when you tip the bottle upside down, a 'partial vacuum' (ie below atmospheric pressure) is created at top of the bottle as the water pours out the bottom. Atmospheric air then 'bubbles through' the mouth of the bottle to compensate. This slows down the flow of water through the mouth of the bottle. Each time ...


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I think you've understood it all, air gets into the bottle faster. Without the vortex, the air is able to pull on the liquid, preventing it from escaping. This is why you can pour orange juice faster if the opening is at the top, rather than the bottom. It also stops it splashing.


2

The effect is real. The heat in the bowl causes the production of steam in the cavity between it and the table. Depending on the temperature, this can be a far more powerful effect than mere thermal expansion of the air. The liquid between the bowl edge and the table acts like a liquid seal for a reasonably smooth and planar table/bowl interface - liquid ...


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Related questions Why does your car lurch toward an oncoming truck as it passes you? Observer stationary A vehicle passing a stationary vehicle can produce a complex pressure wave From MEASUREMENT OF THE AERODYNAMIC PRESSURES PRODUCED BY PASSING TRAINS In this you can see that the stationary vehicle is first pushed away and then sucked back ...


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The relative speed of your car and another car does not matter since your car is affected only by air. Probable explanation. A moving car is producing a wind, blowing in nearly perpendicular direction These streams of are are similar to rain drops. And it is a subject for Galileo transform. If you stay and rain is vertical, it falls on your top. If you ...


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Mayby the moving mass of your car makes it more stabile. The same as a giroscope. The mass of a ciclist is lower so he can experiënce more swaying. Large motorhomes and caravans also sway more when a truck passes. And those are riding at about 50 m/h. So learning while writing , its a combination of surface and streamline, and the stability the moving mass ...


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The light from a fluorescent lamp is produced by an electric current discharging through a gas, typically mercury vapour, which releases photons in the UV-range. These are then absorbed by a thin phosphor coating on the inside of the glass tube, which re-emit a photon in the visible spectrum. In order to generate the required voltage and maintain an arc ...


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If we look at the symmetry of the pear of mass $m$, we can see on the x axis that momentum is conserved because the derivative of its motion in space $x$ is the same from any point we measure it's motion from: $$p_x=m \frac{dx}{dt}$$ On the y axis however, the system is affected by an external field gravity, $g$ which pulls the pear downwards. This removes ...


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[Disclaimer: This answer is a guess, there might be something else going on.] When you boil water in a large enough pot, the water will flow in a toroidal shape, that is, it will rise from the bottom at the center of the pot and go back down at the edges of the pot. As the water flows, it carries some pastas with it, & the pastas are usually alligned ...


2

It is all about wavelength versus tunnel diameter. The wavelength of GPS is about 20cm it would happily propagate in any normal tunnel if it could get in but the earth and other structures absorb it. AM radio (600kHz - 1500kHz) cannot propagate in any normal tunnel because the wavelength is too long (500m-200m) relative to the diameter, and thus gets ...


0

Radio waves are just light of a different frequency. Yes, they are slightly better at reflecting off various surfaces than light, but they still generally travel in straight lines. They don't flow or fill space like a fluid, so there is no reason to believe they'd be good at following you into a tunnel. You generally need line of sight (or something close to ...


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Both of these technologies rely on radio frequency waves, which are blocked by dense matter eg, a hill, a building.


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Since warm air resides above cooler air, when a fan is switched on, it will dissipate the warm air molecules in the room thus slightly increasing the temperature and hence the ac will blow more air out. But after a time the warm air molecules loose their kinetic energy and hence their heat. This results in slight cooling of the room. This cooling, coupled ...


0

If an engine is being used for a task which can make use of all the mechanical energy it produces (such as charging a battery or pumping water as quickly as possible from a supply that's sufficient to avoid cavitation), optimal efficiency will be obtained by having the engine run at wide open throttle but having the load torque match the engine torque when ...


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Another possibility is that a fan would "de-stratify" the air in the room. If the temp sensor was fairly high up a fan would mix the hot and cooler layers of the air in the room making the sensor a bit cooler than it would normally be.


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A fan moves air around. It makes people feel cooler, by causing evaporation of skin moisture (sweat). A fan's motor also gets hotter. Air moving over a thermostat would have no affect (thermostats don't sweat), but the increase in temperature of the fan's motor, would increase the air temperature slightly, causing the air conditioning to work harder. If ...


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The question is therefore : why doesn't a fluid flow out a bottle smoothly ? The "bottleneck" phenomenon is caused by the lack of pressure in the can/bottle. As the liquid flows out, the pressure inside decreases because the volume of the container is fixed. When the pressure inside the bottle reach a given threshold, the outside air tends to flow in the ...


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Because the bag deflates as milk leaves it, the volume of the bag decreases and the pressure remains constant so the milk pours smoothly. When pouring from a can, which does not deform like the bag, the pressure inside the can decreases as liquid leaves the can. The pressure differential creates a potential that pulls air into the can, interrupting the flow ...


1

Static electricity. The cathode ray tube shoots electrons at the back of the TV screen, which becomes negatively charged. To compensate, and try and maintain electrical neutrality, the front of the screen becomes positively charged (the glass acts as a capacitor). As you walk across a nylon carpet, its electrons rub off onto your skin, and the hairs on your ...


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A completely clean silica surface has a very high surface energy and a very high coefficient of friction. However silica surfaces adsorb pretty much anything at the least excuse, so glassware from your cupboard will have a layer of various molecules adsorbed from its environment, and this greatly reduces the coefficient of friction. Dishwash powder is ...


3

I was told a long time ago that the sound is from "twinning" - this is where a metal under large stress experiences a reorientation of grains to relieve stress. However I am not convinced this is the case - typically when the engine parts (catalytic converted being probably the hottest) cools down, it will shrink - and there is some "give" in the mountings ...


1

As you drive, parts of the engine and exhaust system slowly heat up. They probably make cracking noises too, but you can't hear them over the sound of the engine and driving, and the noises-insulated driving cabin. When you stop driving, they cool down, and the hot metal contracts causing a cracking sound.


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On a completely frictionless floor, with the absence of other external forces, the centre of mass of the car will continue in the same trajectory for ever. Hence no steering is possible. However, irrespective of whether the front wheels are rotating or not, turning of the front wheels will produce a counter torque changing the orientation of the car, albeit ...


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Yes you can It is actually possible with a real car, but you would have to be very patient to steer a little bit. Suppose you have built a car with power on the big front wheels to induce a gyroscopic effect. If you rotate the wheels, the direction in which the center of mass is going will not change directly, but the angle in which the rest of the body ...


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Since there is no friction, then it will not affect any other forces that may act on the car. The direction of wind blowing on the car may change its trajectory, as any driver will attest when driving in high winds. Turning the car wheels may have a slight affect on the resultant direction of the force. If the car has curved roof, then it may acts as ...


4

Friction is the only force that would cause the car to move along a different path. On a frictionless surface, the gyroscopic effect could change the orientation of the car a bit, but not the trajectory of the car. In other words, the front car would no longer point along the direction of travel, but would "skid". (That is, if you could call frictionless ...


0

What is required for sparks across a gap is a high voltage, while what determines whether something will do you harm is the amount of current. You can theoretically survive almost any voltage so long as the current is sufficiently low. It's just that most sources of electricity that have high voltages tend also to have high current.


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If the wheels had spun fast enough for a gyroscopic effect to become noticeable, the only result on a frictionless surface (which would be the same without a surface at all) is that when you turn the wheels, the rest of the car would rotate instead of just the front wheels :) You need some reaction force to alter the trajectory, like a sail or surface ...


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No, a car cannot steer on a frictionless surface. This has little to do with gyroscopic action and more to do with conservation of momentum: to turn, even when conserving its speed, the car needs to accelerate at right angles to its motion, which changes the total momentum of the motion. This change in momentum requires a force which, in normal roads, is ...


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For your 2 minute egg timer here on Earth it comes out to be 4 minutes 54 seconds on the Moon because: $t_{Moon} = t_{Earth} \sqrt{6}$ Full explanation below. Q: What is the relationship between hourglass flowrate and local gravity? As in the excellent answer to a related question (hourglass flowrate vs. sand grain size) and this published paper, the ...


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Its a stroboscopic effect. Your eyes can only process information properly which is below a certain amount of frames per second. When wheels rotate slowly we see them in the direction which they are supposed to be rolling in, but when the rotation of the wheel crosses a certain speed, we observe its motion in a totally different way. Assume we observe a ...


0

I'm probably wrong, but I think it would take about 6 times as long, assuming the moon's surface gravity is 1/6th that of Earth: According to http://www.physics.umd.edu/deptinfo/facilities/lecdem/services/demos/demosc5/c5-41.htm, "[d]uring the steady-state sand fall the extra force of sand hitting the bottom very nearly cancels the loss of weight of ...


3

The fluid in the tube is not water as some might think but an organic solvent called Dichloromethane. The reason the bubbles form is due to the fact that the fluid is heated at the base of the tube to it's boiling point which is a low 103.3 F degrees. You can almost get it boiling by holding it in your hand. The bubble is actually the vapor form of the ...


1

There was a recent publication addressing exactly this question. From the abstract: Here, we show that the overall foaming-over process can be divided into three stages where different physical phenomena take place in different time scales: namely, the bubble-collapse (or cavitation) stage, the diffusion-driven stage, and the buoyancy-driven stage.


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John's answer is the closest. Actually it does not matter of the optical index. Materials that has micro holes will reflect light randomly with only narrow boundary between the material and air. When there is water to fill up the holes, some of the light reflected into the material, so your eye will see less light reflected from the material.



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