# Tag Info

Accepted

### How to measure the wavelength of a laser pointer?

Your iPhone is a pretty good grating. I just did a simple experiment with an iPhone, a green laser pointer and a sheet of graph paper. This was the result: The display of the iPhone 6 has a ...
• 118k
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### 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 ...
• 118k
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### 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 (...
• 3,105
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### 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 ...
• 36.6k

### What causes this pattern of sunlight reflected off a table leg?

These are probably caused by minute, periodic variations in the diameter of the table leg, formed by drawing through a die. Any vibration in the process would end up being circumferential waves in the ...
• 3,978
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### 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 ...
• 34.9k

### 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 ...
• 6,071

### 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 ...
• 80.2k
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### 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 ...
• 84.9k

### 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 ...
• 82.6k

### Backyard experiments to falsify the Flat Earth theory

I live close to Lake Erie and often see scenes like in this picture. Note that the bottom of the cargo ship cannot be seen due to the curvature of the Earth.
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### 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 ...
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### What causes this pattern of sunlight reflected off a table leg?

This is a grossly exaggerated illustration of a strictly cylindrical metal tube compared to a cylindrical tube with external diameter variations, like the one you have in your case: Because of those ...
• 1,261

### Backyard experiments to falsify the Flat Earth theory

Related to the Andrea di Biagio answer. Here is a typical flight path for the Beunos Aires-Auckland route. The distance is approximately 10,300 km by the shortest route along a sphere. Direct flights ...
• 120k
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### Why does a Pewter mug keep a beverage hot better than a foam cup?

The metal mug will equilibrate with the water much faster than the foam mug will— but after that the heat has no place to go$^\dagger$ except to be transferred away through radiation or be lost as ...
• 2,942

### 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 ...
• 684
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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. ...
• 28.1k
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### 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. ...
• 11.3k
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### 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 ...
• 8,261
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### 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.
• 34.9k
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### 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 ...
• 325

### 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 ...
• 679

### 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,...
• 3,629

### 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 ...
• 63k
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### 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 ...
• 10.9k

### 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 ...
• 26.9k
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### 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 ...
• 2,111
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: \$...