# Tag Info

35

The short answer is "no". The Titanic was considered "unsinkable" because any four of the sixteen compartments could be flooded and she would still float. These compartments (see picture below) were basically vertical "walls" throughout the ship. If the region between any two walls flooded, the water could not flow to the other compartments (when the flood ...

29

When you would enter the water, you need to "get the water out of the way". Say you need to get 50 liters of water out of the way. In a very short time you need to move this water by a few centimeters. That means the water needs to be accelerated in this short time first, and accelerating 50 kg of matter with your own body in this very short time will deform ...

25

Water is not transparent for deepUV and infrared. From the evolutionary point of view our eye developed to see electromagnetic radiation present at earth in the past (and now) - deep UV and infrared are absorbed by water vapor and other gasses in atmosphere - so there were nothing to see at these wavelengths. Here is a nice explanation on why some things ...

11

The ocean surface is not as hard as the ground but if you drop from a plane, you would hit it with such a high velocity that the pressure would most likely kill you or cause very serious damage. Considering air resistance, the terminal velocity of a human, right before reaching the water, would be at most some $150\text{ m/s}$. If you weigh $70\text{ kg}$, ...

11

Let's look at this another way: you're just moving from one fluid to another. Sounds harmless, right? By specification of the problem, we're at terminal velocity when we hit the water. The force of drag (in both mediums) is roughly: $$F_D\, =\, \tfrac12\, \rho\, v^2\, C_D\, A = \rho \left( \frac{1}{2} v^2 C_D A \right)$$ You can imagine that ...

11

Consider jumping into a swimming pool. Do a barrel-roll (sorry I mean cannon ball, that just kind of slipped out). It's fun, you enter the water nicely and make a huge splash, probably soaking your sister in the process (that'll learn her). Now do a belly flop. Not as fun. You displace exactly the same amount of water in the same time, but this time there is ...

11

To answer this question we also need to know why some things are not transparent and why certain things, water for example, don't behave in this way. A substance's interaction with light is all about interactions between photons and atomic/molecular electrons. Sometimes a photon is absorbed, the absorber lingers a fantasctically short while in an excited ...

8

The overall effect (in particular with regard to this light emission, which really happens – it's not just apparent) is mostly investigated under the name sonoluminescence. Though the process of this luminescence itself remains unsettled, it is for sure that extremely high temperatures are produced at a bubble collapse (in fact, it was conjectured they ...

7

This creates a point of extremely focused energy at the middle point where the bubble collapses. In theory, this point focuses enough energy to trigger nuclear fusion. It is not currently accepted mainstream science to say that collapsing bubbles focus energy enough to cause nuclear fusion. Temperatures over 10,000K can be acheived, but are still well ...

6

Temperature is a measure for how much kinetic energy the molecules in a substance have. If the temperature is high, they are moving pretty fast, if the temperature is low, they are moving a lot slower. If molecules are moving slow, they bundle up and you get a solid. Once you heat it up a bit, the substance starts to become liquid. When you heat it up even ...

6

That is right, deeper the pressure is stronger. But the pressure is not just in one direction it is in every direction. So the velocity will decrease in most cases. But also you have to be aware of the density of the object. You could read this classical description of diving objects "Thrust" on wikipedia. This is a classical effect, in real cases the ...

6

I'm not a physicist. So I am treading very carefully attempting to answer a question here... :) A physical example that may help explain this is rock skipping. When you skip a rock, it will 'bounce' off of the water when at high speeds. Eventually it slows enough to no longer bounce but 'sink' into the water. Picture your body doing the same thing. Your ...

5

In the moist air of the clouds, the water condenses on dust particles. At the altitude where this happens, it is usually below the freezing point of water, so it quickly freezes. If winds and updrafts keep these particles of ice in the moist air, they collect more water. Eventually, the weight of the ice particles overcome the updrafts and fall to the ...

5

This Washington State Department of Transportation page makes it clear that the choppiness is at the very least highly correlated with windstorms and high winds. This page is a good resource as well. The choppiness occurs on the upwind side of the bridge; thus, a south wind (which blows north) will make the south side choppy. The reason for this is that ...

4

While the capillary pressure in soil is many orders of magnitude lower than the atmospheric pressure, you also need to remember that in soil, the water is still in contact with the atmosphere, and thus is at atmospheric pressure plus capillary pressure. Since atmospheric pressure is orders of magnitude larger than capillary pressure, the pressure on the ...

3

Imagine spinning a roulette wheel, but instead of dropping in one ball, you drop in 100. They all rattle around at different speeds, like the molecules in water. You can cool them down by spinning the wheel slower, so they bounce about less; heat them up by spinning faster so they bounce more; you can freeze them by stopping the wheel and waiting till ...

3

If You make a simplified force balance of a sinking box, You can identify two main forces: Force associated with box's weight $F_g$ acting downwards and buoyancy force $F_b$ acting upwards. The formulas are as follows: $F_g=mg$, $F_b=-\rho g V$, where $m$ is the mass of the box, $g$ is the gravitational acceleration, $\rho$ is the density of water, $V$ is ...

3

I think the simplest answer to this question would be that the stream of water has a number of forces acting on it (gravity, air drag) from many directions. Some torque is bound to be produced as the stream falls through the air. If you throw a ball or any small object from a height, it rotates, no matter how you drop it. Same logic applies here. As far as ...

3

An electric field is not experimentally known to change the equilibrium freezing point of water of 0 C. However, water can be supercooled to -40 C, in the absence of nucleation sites. Electric fields affect the freezing of (unstable) supercooled water. See this 2010 article in the journal "Science": http://www.sciencemag.org/content/327/5966/672 and ...

3

You filled the hot water into the bottle, during this time it created steam inside the bottle, moving part of the air out. After closing, the steam cools down and condenses quickly. As some air was pushed out, that creates a vacuum, collapsing the bottle. Another process, which probably has contributed, but would be the main effect when the water is not ...

3

Let's assume a one litre $1000$ W electric kettle, filled with $0.5$ kilograms of water at $20^o$ C: It takes 4.2 joules to warm one gram of water one degree Celsius. So, to warm the $500$ grams of water $80$ degrees from $20$ to $100$ takes $168,000$ joules. The kettle will supply $1000$ joules per second, so it'll take $168$ seconds for the kettle to ...

3

There has to be a few assumptions. Let's assume we are talking about a linear plane wave in relatively deep water. Because the the case where the bottom comes into play the upward hydrostatic force distorts the wave. Picking deep water or insuring the relative depth of d to L (d is average water depth and L is the wavelength of the wave) is $d/L > ... 2 The continuity equation only means that the mass flow rate in equals the mass flow rate out. It does not mean that that flow rate never changes; flow in and flow out can both change simultaneously. For a given pressure drop (pressure upstream minus pressure downstream), the flow rate is proportional to the 4th power of radius, according to the ... 2 Hailstones - or anything like sleet, snow, etc - are formed by the freezing of water. Water droplets rise up, and as the temperature keeps decreasing, they freeze at a certain point into a stone, after which this stone would start falling. Certain studies say that the stone after falling, can enter an area with differenct conditions - causing it to maybe ... 2 The boiling temperature of a liquid is not the temperature at which it can enter the gaseous state. Rather, it is the temperature at which the saturation vapor pressure$e_s$is equal to ambient atmospheric pressure. This is why, for example, water boils at lower temperatures at higher altitudes. Furthermore, water is always evaporating. It is also ... 2 It may actually work, as evaporating liquids need heat to evaporate, and water will somewhat evaporate even in the fridge. I am not sure it works in practice, because the paper also causes an adverse effect, it provides insulation, Hard to tell which effect is dominant. I'm pretty sure that the balance of both effects depends in a very large part on the ... 2 The relevant equation is the kinematics with linear drag. In this case, there is a resistant force that acts opposite gravity (i.e., upwards) and is linear to the velocity at which it travels: $$\mathbf F_D=-b\mathbf v$$ where$b\$ is some fluid- and object-dependent constant. Using Newton's 2nd law, $$m\ddot{\mathbf x}=m\mathbf g - b\dot{\mathbf x}$$ If ...

1

I believe the 'urban legend' you are referring to is about cooling a bottle when you do not have a refrigerator. On a hot and windy day you could store your bottle in the sunlight, but it would be better in the shade, but if you really wanted to cool the bottle by a few more degrees, the 'myth' says wrap it in wet paper or cloth. During the time when the ...

1

In the case of a pebble falling from some height into water, I believe surface tension will be altogether negligible. You should calculate the Weber number to check this, http://en.wikipedia.org/wiki/Weber_number The dominant effect will be the pressure generated by the displacement of water by the pebble entering. Again, I am not sure that the viscous drag ...

1

Let's start with the evaporation of water (or sublimation, in this case). Carbon dioxide exists as a gas at normal temperature and pressure. If it is compressed and cooled, you make dry ice. When dry ice heats up, the solid becomes a gas directly (any liquid is from water condensing on the dry ice). This process is called sublimation. Water (or ice) can ...

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