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85 votes

Why is the vibration in my wire acting so oddly?

Your wire is not quite round (almost no wire is), and consequently it has a different vibration frequency along its principal axes1. You are exciting a mixture of the two modes of oscillation by ...
Floris's user avatar
  • 119k
78 votes

Why does water falling slowly from a tap bend inwards?

You can actually predict the shape of the profile precisely using the arguments you mention above, which are by and large correct. To do so, you can make the following assumptions: Neglect viscosity (...
aghostinthefigures's user avatar
59 votes

Why is Microwaved mac & cheese burnt where they touch?

I get the same thing reheating some discs of glazed carrots. And there are several videos of folks doing this intentionally with grapes. An article published last year in PNAS says this will happen ...
BowlOfRed's user avatar
  • 40.3k
49 votes

Why does a ping pong ball bounce higher when it is dropped together with a cup of water?

I've confirmed the experiment, using a McD_n_lds paper drinks cup and a beer can hollow plastic ball of about $5\mathrm{g}$, of about the same diameter as a ping pong ball (PPB): The observed effect ...
Gert's user avatar
  • 35.3k
45 votes

Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?

Take advantage of the large difference in thermal conductivity between copper and stainless steel (approximately $400$ and $16$ $\mathrm{Wm^{-1}K^{-1}}$ respectively). If you put one end of a metal ...
jkej's user avatar
  • 6,158
42 votes

What's the problem with my Young slits experiment?

The angle between maxima in the double-slit pattern is $$ \theta \approx \frac\lambda d $$ for wavelength $\lambda$ and slit separation $d$. I wild-guess that the slits in your photograph are about 5 ...
rob's user avatar
  • 90.7k
41 votes

Why won't this electromagnet home experiment work?

The insulation on the pipe cleaner is fine (I tested it) and the only difficulty is getting good electrical contact at the ends. It is best to burn off the end insulation and then scrape the metal ...
Farcher's user avatar
  • 96.8k
37 votes

Why does water falling slowly from a tap bend inwards?

To enlarge slightly upon @aghostinthefigures' excellent exposition, for small gravity-driven jets the flow does not go turbulent- instead, it is subject to rayleigh instability when its cross-section ...
niels nielsen's user avatar
32 votes

Spinning gyroscope loses weight?

You are substantially overstating the precision of your measurements. The readings changed rapidly so they had to be read by stepping through videos of the experiment. What you mean is that you ...
Dale's user avatar
  • 102k
31 votes

Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?

Why not density? At least for a quick check and as for the title question. You are dealing with about < 8 and 9 g per cubic cm, respectively for steel and copper. Not overly laborious and ...
Alchimista's user avatar
  • 1,729
29 votes

Cooling a cup of coffee with help of a spoon

I recently made a slightly different test, also testing temperature in a cup of coffee: Where: Green area is where I think the coffee is in a drinkable temperature Purple is no cooling. It's simply ...
nammerkage's user avatar
29 votes

Calculating temperature when it is lower than your thermometers can read?

The freezing point of water ethylene glycol mixtures depends in the concentration of ethylene glycol. You can find data for this on the Engineering Toolbox web site (a valuable source of all sorts of ...
John Rennie's user avatar
25 votes

Explaining The Unbelievable Pendulum Catch

TL;DR: Mass ratio = 14 is not particularly special, but it is in a special region of mass ratios (about 11 to 14) that has optimal properties to wind the rope around the finger as much as possible. ...
Wolpertinger's user avatar
  • 11.6k
25 votes

Radiation from Sticky Tape

Triboluminescence. The exact mechanism in sticky stuff is still uncertain, but it's not just light. It makes X-rays. Fractoluminescence is the version that applies only to fracturing crystals (e.g. ...
JEB's user avatar
  • 34.3k
24 votes

What are these alternating bright and dark rings in fluorescent lamp?

This reminds me of the Franck-Hertz experiment where similar patterns occur. At low voltage, the free electrons in the tube will be accelerated by the voltage until they have enough energy to excite ...
Martin Ueding's user avatar
23 votes

The process of burning and increasing weight

For steel wool the combustion reaction is roughly: $$\require{mhchem} \ce{2 Fe (s) + 3/2 O2 (g) -> Fe2O3 (s)}$$ So the object 'absorbs' (and chemically binds) air oxygen and thus gains weight.
Gert's user avatar
  • 35.3k
21 votes

Cooling a cup of coffee with help of a spoon

There are many answers and even experimental data, but there is no mathematical model. I will fill this gap, add a few models explaining the experimental data. The simplest model is laminar convection,...
Alex Trounev's user avatar
  • 3,754
21 votes

How come I never see cosmic rays in steam like they appear in a cloud chamber?

Cloud chambers require a supersaturated environment such as one created by cooling a sealed chamber filled with alcohol vapor. The high velocity cosmic ray particles ionize the gas molecules they come ...
Stel's user avatar
  • 325
20 votes

Easy to perform quantitative experiments at home

The simple pendulum experiment is very simple to perform, from which a lot of conclusions can be drawn. An object like a ball, like an apple can be used as a weight at the bottom, and a string can be ...
Sumant's user avatar
  • 689
19 votes

Is it possible to show a diffraction caustic as a home experiment / lecture demonstration?

This may be easier than you think. I took this photo (with my iPhone) of a cusp caustic which I generated by darkening the bathroom, wetting the mirror, and angling the laser pointer so it hit a water ...
Dan Piponi's user avatar
  • 2,188
19 votes

Heating cup in microwave?

It's probably because your milk cup is made of a material that is a relatively good thermal insulator. First of all, the microwaves directly heat the milk, and not the cup, as long as the cup is made ...
Bob D's user avatar
  • 72.5k
19 votes

If you were encased in an iron block and dropped from a building, what would happen?

The box stops abruptly when it hits the pavement (Let's say, for sake of argument, that it hits an outcrop of bedrock that happens to stick up right next to the building.) The force between the box ...
Solomon Slow's user avatar
  • 14.6k
18 votes

A curious phenomenon with a stick

The explanation is the interplay between the friction forces and the distribution of the weight of the ruler as the fingers move along it. The two fingers do not share the weight $W$ of the ruler ...
sammy gerbil's user avatar
  • 27.3k
18 votes

Why does a ping pong ball bounce higher when it is dropped together with a cup of water?

As mentioned in the comments above, the ball in the cup is similar to Galilean Cannon. The maximum height to which the ball can bounce $h_{max}$ can be estimated using the law of energy conservation: $...
atarasenko's user avatar
  • 1,005
17 votes

Fractal patterns on water

It looks a lot like the result of diffusion-limited aggregation or more specifically diffusion limited cluster aggregation: Image source. If that's indeed the process responsible for the patterns, ...
stafusa's user avatar
  • 12.4k
17 votes

Are there physical properties that can be used to differentiate stainless steel from copper in a home environment?

What about Eddy currents? If you've got a pair of strong neodymium magnets (doesn't everyone?) - move the straw in between two magnets with their poles opposing. Copper/Aluminum will have a strong ...
user3772748's user avatar
17 votes

Does soap repel water?

tl;dr- When the soap touched the water, part of it dissolved, reducing the local surface tension. Since the higher surface tension further away from the soap pulled more strongly than the weaker ...
Nat's user avatar
  • 4,650
17 votes

How do we know what physics or science textbook said is correct?

Strictly speaking, you don't. All science is tentative and subject to change should new evidence or new insights arise. All conclusions are not only open to challenge, but it is part of the process ...
Nullius in Verba's user avatar

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