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57

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 ...


53

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 ...


47

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 ...


28

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 ...


27

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 ...


22

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 ...


10

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 ...


6

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 ...


5

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 ...


4

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.


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 ...


4

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 ...


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 ...


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 ...


3

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 ...


3

[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 ...


3

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 ...


2

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 ...


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 ...


2

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 ...


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 ...


2

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


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 ...


2

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 ...


2

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 ...


1

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 ...


1

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 ...


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 ...


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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