# Tag Info

781

So, I decided to try it out. I used Audacity to record ~5 seconds of sound that resulted when I dropped a penny, nickel, dime and quarter onto my table, each 10 times. I then computed the power spectral density of the sound and obtained the following results: I also recorded 5 seconds of me not dropping a coin 10 times to get a background measurement. In ...

314

I'd say the culprit is the contact area between the two surfaces relative to the deformation. When there are other pieces of paper below it, all the paper is able to deform when you push down; because the paper is fairly soft and deformable fiber. If there is more soft deformable paper below it, the layers are able to bend and stretch more. (A simplified ...

311

If you have the dimensions and material of an object, you can compute both the mass and the normal vibration modes. Just the mass is not enough - a large paper "coin" will have a different fundamental frequency than a small tungsten sphere. A summary of everything that comes below - the result of several edits, and including a nice interaction with the ...

260

There is no tidal bulge. This was one of Newton's few mistakes. Newton did get the tidal forcing function correct, but the response to that forcing in the oceans: completely wrong. Newton's equilibrium theory of the tides with its two tidal bulges is falsified by observation. If this hypothesis was correct, high tide would occur when the Moon is at zenith ...

248

Congratulations, you found an inverted pyramid ice spike, sometimes called an ice vase! The Bally-Dorsey model of how it happens is that first the surface of the water freezes, sealing off the water below except for a small opening. If the freezing rate is high enough the expansion of ice under the surface will increase pressure (since the ice is less dense ...

238

Understanding why this works turns out to be quite deep. This answer is kind of a long story, but there's no maths. At the end ('A more formal approach') there is an outline of how the maths works: skip to that if you don't want the story. Insect geometry Consider a little insect or something who lives on the surface of the paper. This insect can't see ...

234

To complement Floris's answer, here's a quick animation showing how the shadow changes with the size of the light source. In this animation, I've forced the intensity of the light to vary inversely with the surface area, so the total power output is constant ($P \approx 62.83 \, \mathrm{W}$). This is why the object (Suzanne) doesn't appear to get any ...

228

A physicist working at Motorola actually did this experiment as part of a promotional push for shatter-proof screens. This same physicist had previously written a paper on the same question, applied to the classic "buttered toast" problem (does toast really land butter side down?). The short answer is: the way the phone lands depends on how it is oriented ...

216

A couple of decades ago I was peripherally involved with some research on the properties of ice cream being done by the company Walls in the UK. The work was on relating the consistency of the ice cream to the microstructure, so it was quite closely related to your question. Anyhow, ice cream has a surprisingly complicated microstructure. It contains ice ...

210

You are getting reflections from the front (glass surface) and back (mirrored) surface, including (multiple) internal reflections: It should be obvious from this diagram that the spots will be further apart as you move to a more glancing angle of incidence. Depending on the polarization of the laser pointer, there is an angle (the Brewster angle) where you ...

194

Since this is PhysicsSE, I am happy with an answer based purely on theoretical analysis of the forces involved. Oh boy, time to spend way too much time on a response. Lets assume the simple model of a peg that makes an angle $\alpha$ with the wall and ends in a circular cap of radius $R$. Then a towel of total length $L$ and linear mass density $\rho$ has ...

182

The "stuff" sticks to itself better than it sticks to the cookie. Now if you pull the cookies apart, you create a region of local stress, and one of the two interfaces will begin to unstick. At that point, you get something called "stress concentration" at the tip of the crack (red arrow) - where the tensile force concentrates: To get the stuff to start ...

175

The fibers in a rope strand are 'layed' stretched out straight, then twisted. Multiple strands are combined, by twisting, to make the rope. When a rope is pulled taut, all the fibers have similar stress, and all contribute nearly equally to the tensile strength. When in a knot, however, the fibers on the inside of the curve are not in tension, and those on ...

169

You get burned because energy is transferred from the hot object to your hand until they are both at the same temperature. The more energy transferred, the more damage done to you. Aluminium, like most metals, has a lower heat capacity than water (ie you) so transferring a small amount of energy lowers the temperature of aluminium more than it heats you (...

168

Because the real situation looks a lot more like this: Your pen is (presumably) not made of mirror-like polished metal, but rather of something like wood or plastic that reflects light diffusely. This means that the light from each part of the pen is scattered all over the paper (and, of course, in other directions too), so it won't project a clear image ...

163

Both thawing and evaporation involve heat exchange between the stone tile, the water sitting atop the stone tile, any water that's been absorbed by the stone tile, and the air around. The basic reason that the center and the edges of the tile evaporate differently is that the gaps between the tiles change the way that heat is exchanged there. However the ...

161

What you are seeing is not actually vapor - vapor is invisible. The mist seen above boiling water, commonly but inaccurately called vapor, is actually made of tiny droplets of liquid water, formed when the vapor cools down and condenses. While the stove is on, the constant influx of vapor from the boiling water keeps the air above it hot, so condensation is ...

155

Paper, especially when freshly cut, might appear to have smooth edges, but in reality, its edges are serrated (i.e. having a jagged edge), making it more like a saw than a smooth blade. This enables the paper to tear through the skin fairly easily. The jagged edges greatly reduce contact area, and causes the pressure applied to be rather high. Thus, the ...

138

Get someone to relax their neck as much as possible, stabilize their torso, then punch them in the head with a calibrated fist and measure the initial acceleration. Apply $\vec F=m \vec a$.

137

Look at CandiedOrange's answer This answer was accepted, but CandiedOrange has the right answer. See this document page 21: The second way in which reflection can interfer e with controller’s vision is light sources within the cab (or direct sunlight that enters the cab), which can cause disturbing reflections during either day or night ...

135

In everyday life glass surfaces are always covered by a layer of, well, crud. Glass surfaces are exceedingly high energy surfaces due to the high density of polar hydroxyl groups and they attract pretty much anything. This means that outside of a colloid science laboratory you will never encounter a clean glass surface. I spent many years carrying out ...

134

Of course, by common sense, if you put together two objects with masses $m_1$ and $m_2$, and nothing comes out, then you end up with mass $m_1 + m_2$. Weights are a little more complicated because of buoyant forces. All objects on Earth continuously experience a buoyant force from the volume of the air they displace. This doesn't matter as long as volume ...

133

As you said, it's probably not magnetism if the balls are free to rotate; there is no reason they wouldn't just flip over and stick together, north to south. You can test this by buying some of those toy magnetic balls. The repulsive configurations are highly unstable and turn attractive with the slightest touch. I'm going to go out on a limb and say it's ...

132

Your derivation is composed of correct statements and indeed, if something is known to act as a lubricant, we want the viscosity to be as low as possible because the friction will be reduced in this way. For example, honey is a bad lubricant because it's too viscous. However, your derivation isn't the whole story. The second condition is that the two ...

127

A 40W incandescent light bulb has a luminous efficiency of 1.9%. That means only 1.9%, or 0.76W, of the energy consumed by the bulb ends up as visible light. LED bulbs have an efficiency of around 10% - the efficiency depends on the design and can be as high as 15% or as low as 8%. So a 6W LED bulb will produce between 0.9 and 0.48W of visible light. The ...

125

In large part because under normal circumstances water doesn't get hotter than boiling - at that point it becomes steam, as you know. You can add heat and boil it away faster, but the water can only get so hot. When you remove the source of heat the water will quickly drop below this threshold. You're right on the knife edge of temperature.

125

While it's true that the difference in specific heat capacity is to your advantage, its effect is really dwarfed by the mass difference. Typical aluminium foil is 0.016 mm thick and weighs 0.043 kg/m², while human skin is about 1.3 mm thick (and even thicker on your palms/fingers) and weighs about 1.3 kg/m², assuming 1000 kg/m³ density. So there's about 30 ...

121

There is some contribution from the friction of the various surfaces, but the main factor is the balancing of weight. It's important to note that the hook is set slightly away from the wall, which allows almost the entire weight of the towel to move alongside or behind the front of the hook tip. The manner in which the towel is cast over the tip of the ...

120

You have created a rather poor pinhole camera (camera obscura). You can see an "image" of the sky, a green space (trees) and even a reddish brown blur that is your driveway. This is not diffraction or refraction - it's geometrical (classical) optics. Because the hole is pretty big, you see a very blurry image. But basically, the light from the sky ...

113

As said by John Rennie, it has to do with the shadows' fuzzyness. However, that alone doesn't quite explain it. Let's do this with actual fuzzyness: I've simulated shadow by blurring each shape and multiplying the brightness values1. Here's the GIMP file, so you can see how exactly and move the shapes around yourself. I don't think you'd say there's any ...

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