Wikipedia:Reference desk/Archives/Science/2022 November 15

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November 15

The amplitude of AC electricity.

DC electricity is AC electricity with a frequency of 0. So if frequency of 0, is a straight line, with 0 amplitude. Then AC electricity, is like a sine wave. What happens when you increase the amplitude? Increase in amps, or watts? 67.165.185.178 (talk) 00:07, 15 November 2022 (UTC).

DC electricity would not have an amplitude of 0. You can measure the amplitude in Volts, Watts or Amps as you suspect. If you double the voltage when there is a resistive load, you will double the current (in Amps) and quadruple the power (in Watts). You can look at Root_mean_square#Average_power for how to work out power when the amplitude is fluctuating. Graeme Bartlett (talk) 00:31, 15 November 2022 (UTC)

What would a sine curve graph look like with 0 frequency but has an amplitude? 67.165.185.178 (talk) 02:53, 15 November 2022 (UTC).

$f(\theta )$ that is invariant for $\theta$ and with non-zero amplitude is a horizontal line at some y-axis value, just like DC current (or voltage, or whatever you're measuring). DMacks (talk) 03:00, 15 November 2022 (UTC)

Most definitions of amplitude assume a varying time signal, but in the case of a sine wave are proportional to the width of the range of the signal. For a constant signal, that width equals 0. Only using the sense of "peak amplitude" with another reference value than mean value will give a non-zero amplitude.  --Lambiam 08:47, 16 November 2022 (UTC)

But I'm looking for an illustration. Of a sine curve with 0 frequency, but having an amplitude? 67.165.185.178 (talk) 11:53, 18 November 2022 (UTC).

The premise that DC is a special case of AC is wrong. If it ain't got the vibe, it ain't alternating. DC can be seen as a limiting case of AC, though. The wave form of a pure-sine AC wave of amplitude $a$ and frequency $f$ can be expressed mathematically as a function of time $t$ by $i=a\sin(2\pi ft+\varphi ).$ In this formula, $\varphi$ stands for whatever the phase happens to be at time $t=0.$ As the frequency gets arbitrarily close to 0, we obtain in the limit: $\textstyle {\lim _{f\to 0}}\,i=a\sin \varphi ,$ so the current does not depend on the time but is constant. (The convergence to this limit is not uniform.) The strength can "freeze" to any value in the range from $-a$ to $+a,$ just as when a lightning strike halts the clockwork of a clock tower, it can freeze the clock at 10:04 or any other display of its hands.  --Lambiam 07:52, 15 November 2022 (UTC)

Wait, can there be electricity with a frequency of 0? Can that be done for both AC and DC? 67.165.185.178 (talk) 02:36, 17 November 2022 (UTC).

As explained above, a frequency of 0 means a constant value. By definition, for a current that means the same as being a direct current. Alternating current has, by definition, a frequency that is non-zero.  --Lambiam 09:25, 17 November 2022 (UTC)

What kind of small animals could hurt a Coelophysis?

What kind of small animals from the chinle formation have the weaponry to give nasty wounds to a Coelophysis that could get infected and cause the dinosaur to die? CuddleKing1993 (talk) 03:42, 15 November 2022 (UTC)

Another coelophysid. Probably most contemporaneous small predatory theropods.  --Lambiam 07:59, 15 November 2022 (UTC)

What about other kinds of animals, like animals it would prey on? CuddleKing1993 (talk) 01:08, 16 November 2022 (UTC)

Paleobiota of the Chinle Formation should give you an idea of what other animals were living at the same time. Mikenorton (talk) 17:25, 16 November 2022 (UTC)

Science experiment

My mom and I did a science experiment. We took a banana's peel off. The banana was supposed to turn into mush faster because the peel kept it safe. However, it still didn't turn into mush! Why is that? 67.215.28.226 (talk) 23:30, 15 November 2022 (UTC)

Would go faster if you increase the temperature. 67.165.185.178 (talk) 23:50, 15 November 2022 (UTC).

Why do I need to increase the temperature? 67.215.28.226 (talk) 05:24, 16 November 2022 (UTC)

You don't need to; it's just another science experiment. It is even faster if you step on the banana. :)  --Lambiam 08:22, 16 November 2022 (UTC)

A possible explanation is that the supposition is wrong. Bananas normally turn soft because of natural ripening, which turns the starch in the banana into sugar (see Cavendish banana § Uses). Removing the peel does not speed up the ripening process.  --Lambiam 08:28, 16 November 2022 (UTC)

Thank you. And what I've used was indeed a Cavendish banana. 67.215.28.226 (talk) 18:35, 16 November 2022 (UTC)

An experiment is a procedure carried out to support or refute a hypothesis. You and your mom succeeded in refuting your hypothesis, so your experiment has succeeded in what you set out to do. Shantavira|^{feed me} 09:40, 16 November 2022 (UTC)

Others have commented on the ideas that might give the outcome you observed. I'll comment on how you are testing your idea. You say it was expected to turn into mush faster. What's the basis or expectation for how long it would usually take? There can be a lot of natural variation in the original banana (how ripe it was when you started, how warm/cool it had been stored, whether the peel might already be damaged, etc.). So you're off to a good start: you made a prediction, did an experiment, and have a result. To make it a more complete experiment, you need what's called a control case to make sure you have a good reference for comparison. For example, if you have two bananas from the same original bunch, you can be pretty sure they are at equal starting conditions when you get them. Therefore "peel one, don't peel the other" and see which one becomes mush first. That's a more direct comparison than simply "the one banana I had didn't turn to mush in a certain amount of time". DMacks (talk) 09:53, 16 November 2022 (UTC)

If I remember it well, banana ripening is associated to emissions of ethylene. Other fruits, including other bananas, may emit ethylene, so both the test banana and the control banana should be in the same conditions, including distance to other bananas and fruits. --Error (talk) 18:45, 16 November 2022 (UTC)

• One of the things to remember about actual science is that it needs to be repeatable to be meaningful. That's because variation always occurs, so if you and your mom ran the experiment only one time, from a scientific perspective, that's a meaningless result. You'd have to run it multiple times to look for trends and repeatability, to smooth out errors, that sort of thing. Some scientific disciplines have even formalized how many times a result needs to be repeatable before they will confirm it as a result. In particle physics, this is the 5 sigma standard, which means that you've done enough experiments to reduce the uncertainty of the results to one part in about 3.5 million. For a home-brew experiment like your banana experiment, that's plainly silly, but if you're going to get reliable results, I would expect the experiment to be run at least a half dozen times to get something that you could be confident in. --Jayron32 13:18, 18 November 2022 (UTC)