Leave milk unrefrigerated, and it will quickly spoil, so wouldn’t milk or cream spoil extremely fast in hot coffee? Or is it hot enough that the bacteria can’t survive. Would coffee that’s just luke warm last as long before going bad?

From my experience with microcontrollers all that I know is that I tell the microcontroller what to do in my code and it does it. My question is how does it understand what I tell it to do. OK so I know it has something to do with hexadecimal and tons of transistors which act as OR , NOR gates , etc. I also know that a compiler converts your high level code to hex. But between hex and microcontroller is where I am totally lost. How can such a tiny device understand instructions?

Lets take the simplest program: Flash an LED once a second . How on earth can the device understand instructions. And how can that same microcontroller understand an almost infinite combination of instructions? I’m vexed my this question.

We’ve got a PBX with a simple headphone jack “line in” that plays on-hold music. It’s attached to an iPod that plays on loop.

Whenever the iPod is plugged into the wall we get an annoying humming noise on the PBX. This also was evident on our old music system which was a simple CD player, so it’s not the ipod’s fault.

This noise is absent when listening to the ipod via headphones + plugged in.

We have tried relocating the ipod plug to other outlets with similar results (next effort will be to plug it into a very long extension cord and try that). What gives?

I was thinking that since the ipod plug is only a 2 pronger, that perhaps it’s using the ground from the PBX? Apple doesn’t make a 3 prong for the ipod, but I think I can use the cord from my macbook pro which is a 3 pronger (will update if that works)...

If temperature is relative motion between molecules, why doesn’t stirring a cup of water heat it up?

When you staple paper, the staple gets smashed into the bottom stapler half, but on a box, you can’t have the bottom of a stapler inside.

Do you lose efficiency by accelerating and decelerating? For instance, going faster when no cop is in sight, and slowing down when not much road ahead can be seen? What about on hills, is it better to maintain speed than slow down on the uphills and speed up on the downhills? Another way to ask is to say whether it’s better to maintain gas pedal position or speedometer position. And if there’s a difference, is it significant?

What is the price for accelerating faster (pedal to the metal) vs. slow acceleration? This probably depends on manual vs. automatic.

Before you write me off on this, I’ve already gotten unsatisfactory answers from friends getting phds in fluid dynamics… still need somebody to break it down for me. What causes lift? Is it because the length of the top of the wing is longer, which stretches the air over a larger volume, making the pressure below higher? Or is it that the wing hits the air at an angle? Bonus points for not using the phrase “conservation of momentum.”

Here’s my current A/C operation:
Before I leave for work in the morning, I kick up my A/C to 77F.
When I get home from work, I set the temp back down to 72F.

Assuming that the external environment will always be adding heat to my apartment (e.g. environmental effects held constant), is this operation more or less energy efficient than just leaving it @ 72 all day?

Maybe the question really is: are A/C units more efficient in the short run (running for a few minutes to cool form 73 to 72) or in the long run (running for many minutes cooling from 77 to 72)?

As far as I know, my electric co does not offer peak/off-peak billing ($ per kWh per hour of day held constant)

Even though the wick is coated with wax, what keeps the fire from burning a hole down the middle of the candle? What governs the length of wick? It always seems to be about a half inch….

If you let a cup of coffee sit for a while, come back and take a swig, will you get a mouth full of caffeine or none at all?

I.e. Will caffeine sink or float in water?

If a gun fires and somebody claps their hands at one end of a football field, the sound from both will reach the other side at exactly the same time. It seems like the explosion from the gun would push harder on the air, so why doesn’t it go faster? wikipedia/speed_of_sound says that the speed is a function of stiffness and density, but not amplitude… why?

How could you go faster than the wind doing the pushing??

The typical explanation for these is that noise will get on two signal lines and be subtracted out at the input. But any voltage signal is just a difference… On a regular 2-wire cable, it seems like any noise that gets on the signal line would also get on the ground wire and be subtracted off. Why the need for 3 wire balanced or differential inputs?

How is it that you can dissolve more sugar in water when it’s hotter? If a molecule of sugar reacts with a certain number of water molecules, how does a higher temperature allow more sugar to react? If a street has 5 garages and 5 cars, a hotter day wouldn’t help more cars fit into the garages…

Take two sine waves of the same frequency, shift one, multiply it by something, and then add it to the other one… you always get another sine wave out. Try doing that with any other shape wave and you’ll get a completely different shape out.

Speculation: If a magnetic door lock has an electromagnet that’s on constantly, it seems like that would be completely insecure in a power outage, and also waste electricity constantly. Or is there a permanent magnet that gets repelled when the door is unlocked?

If you want to get the coolest coffee, the top seems like it would be the coolest because it’s exposed to cool air, but on the other hand, heat rises…

If you look in your electrical cabinet, you’ll see that all the ground wires and ‘common’ or neutral wires connect, so why bother having a separate ‘ground’ when it’s the same wire as the neutral line?