Recent comments in /f/askscience

mfb- t1_j347et8 wrote

Reply to How do you optimize a rocket or space vehicle liftoff? by seriousnotshirley

A lot of simulations. There is essentially nothing that only has advantages or disadvantages, so you need to consider tons of options.

If you have a given rocket design and a fixed mission: Launch at full power - this is a very wasteful part of the flight and you want to gain speed as soon as possible. Acceleration will (almost) always be low because the rocket is still full of propellant. Tilt a bit to the side and follow an approximate gravity turn. Throttle down before reaching the maximum aerodynamic pressure if needed for safety. Typically this is only a pretty short period.

Some more things to consider, in addition to what you mentioned:

  • Different payloads have different requirements but you don't want too many rocket variants.
  • Making the rocket more robust against weather helps with launch opportunities but might reduce the performance.
  • Typically components are shipped from construction site to launch site, favoring a smaller diameter - but that makes it more susceptible to wind.
  • Launch site selection matters, too.
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MidnightAdventurer t1_j33znr5 wrote

Reply to comment by train1111818 in How fast would a body fall to earth if there was no atmosphere to stop it from accelerating past a terminal velocity? by straubzilla

If you're starting from rest and falling towards a planet, then you will accelerate faster until you hit. Remember that gravity gets lower the further away you are and eventually you will be far enough away that the planet's pull on you isn't relevant anymore - escape velocity is how fast you would accelerate to if you started at the point where you are only just falling towards the planet (simplifying a lot but close enough)

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fliguana t1_j33uv8a wrote

Reply to How do you optimize a rocket or space vehicle liftoff? by seriousnotshirley

Rockets launch at full power. The effect of air resistance comes into play for some, more fragile rockets which cannot withstand maximum frontal forces, so there is a point during ascend (maxQ), when engines are temporarily dialed back to reduce acceleration.

A few seconds later, the max power is restored in less dense atmosphere.

Why the let-off is stepped rather than gradual is a mystery to me, perhaps some optimization is available. Also relevant the path of the rocket - the more vertically it launches, the faster it clears the atmosphere, but then longer takes to gain lateral orbital speed.

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chloralhydrat t1_j33r6di wrote

Reply to Where does all of the snot come from when you have a cold? by Dunkachin0

... what is interesting as well is the colour of the mucus produced when you have cold. Especially during sinus infection, large amount of green snot is produced. But the mucus should be colourless, so where does this come from? The answer is, that it contains dead white blood cells - a result of a fight your immune system is waging against the infection. The colour itself is caused by haem (the same chemical, which carries iron and binds oxygen in haemoglobin). As a quite conjungated aromatic system, haem derivatives are often deeply coloured. What is really cool, is that the haem in the snot is mostly contained in an enzyme, which produces hypochlorite ions by oxidation of chloride (haem is usually contained in redox-active enzymes). So your body produces its own "bleach" (active agens in bleach is the hypochlorite) to disinfect your innards :)

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JJdaCool t1_j33g215 wrote

Reply to How does dish soap eliminate bacteria? by [deleted]

From my understanding many soaps contain sulfactants and surfactants that disrupt the sulfur and surface tensions in the outer membrane of bacteria cells.

This disruption, in addition to lipid interactions and mechanical abrasion, makes many bacteria weaker; when the bacteria is then transferred plate to plate and to sponge it is less able to survive or reproduce.

Also after bacteria interact with soaps, regular water can act as a mild solvent further degrading the bacteria (and washing it away).

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chemipedia t1_j33ejs9 wrote

Reply to comment by charlesfire in Where does all of the snot come from when you have a cold? by Dunkachin0

First of all, I’m a little mad that I read that and therefore absorbed the idea. Second of all, how dare you! Now I’m curious about snot-based jello?!

The solidifying effect of animal gelatin is from the molecules twisting in a way that catches on to one another as they cool down. They form sites that allow for the phase-shift from liquid to solid as the temperature lowers. With mucins, the phase shift is more complex and we apparently don’t fully understand how it happens, but we think it involves polymerization stabilized by disulfide bridges and it’s definitely more complex than a temperature-based physical reaction like with gelatin.

So like … it depends on what you have in your kitchen? Maybe? Would it still be considered jello? Also, I couldn’t find a good answer on max viscosity of mucin gel formation so I’m unable to say whether it would be more like traditional jello or more like snot pudding.

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