126
votes
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
85
votes
Accepted
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
78
votes
Accepted
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
59
votes
Accepted
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
54
votes
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
49
votes
Accepted
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
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 ...
- 6,071
41
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♦
- 80.2k
40
votes
Accepted
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
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 ...
- 82.6k
33
votes
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.
- 1,801
32
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 ...
- 1,719
30
votes
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
30
votes
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
29
votes
Accepted
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
27
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 ...
- 684
26
votes
Accepted
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. ...
- 28.1k
25
votes
Accepted
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
24
votes
Accepted
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
23
votes
Accepted
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
21
votes
Accepted
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
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 ...
- 679
19
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,...
- 3,629
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 ...
- 63k
19
votes
Accepted
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
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 ...
- 26.9k
18
votes
Accepted
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
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:
$...
- 1,009
Only top scored, non community-wiki answers of a minimum length are eligible