58 votes
Accepted

Why do rotten eggs float in water?

The domestic chicken's egg shell has about 7000 pores that allow the embryo to breathe. When an egg rots the yolk and surrounding materials decompose and they give off gasses which can pass through ...
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54 votes

Why do we "feel" steam at 100 °C as hotter than water at 100 °C?

TL;DR: You have probably not been exposed to 100°C water in either phase and even if you had, you could not have reasonably felt its temperature on account of receiving a third-degree burn. Hot water ...
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  • 4,245
48 votes
Accepted

Why do we "feel" steam at 100 °C as hotter than water at 100 °C?

What we define as "hot" or "cold" is the transfer of energy -- how much (quantity) and how fast (rate of transfer) -- and how it raises our temperature. The more energy that is ...
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  • 6,288
47 votes

Why does twisting a cork make it easier to remove from a bottle?

When the cork is stuck and stationary, it is static friction which is culpable in keeping it fixed. As soon as the cork moves - in any direction - the static friction is replaced by kinetic friction. ...
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  • 46.3k
45 votes
Accepted

If I push someone, what fundamental force do I create?

If I push someone, what fundamental force do I create? When a human pushes a object through physical contact, the nature of the force between the human and object is electromagnetic. Atoms consist of ...
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44 votes

How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?

There are a few reasons why small speakers have trouble creating bass. Bass is directly proportional to the amount of air the speaker can move. So you want a large cone that can move a large distance....
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  • 3,220
43 votes

How would physics explain why I can't un-fold paper?

Your example is not an ideal one to illustrate the underlying principles, as the factors that prevent you from unfolding the paper involve many trillions of molecular interactions within the paper, ...
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  • 18.2k
39 votes

Slipstreaming - is there a penalty?

The opposite seems to be true. There was, or maybe still is, a company that was looking into designing a system that allowed two semi trucks to "link" to each other (basically the truck in ...
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  • 1,170
39 votes

What's the heat capacity of pizza?

I would imagine the high heat capacity of water, its high latent heat of vaporization and the large amount of it present would dwarf everything else present in the pizza. Water has 10x the heat ...
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  • 6,874
36 votes

Why does running spend more energy than walking?

The basic reason is that an ideal object does work in the physics sense, but a biological entity has so many, many, ways it doesn't behave like an ideal object. One can estimate and calculate, but ...
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  • 4,087
36 votes

Slipstreaming - is there a penalty?

For cycling, there doesn't seem to be a penalty, but even a small advantage to the rider in front of a group. Computational fluid dynamics simulations and wind tunnel testing have shown air resistance ...
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  • 461
34 votes

What's the physics behind the jumps with seemingly non-conserved angular momentum?

To explain how orientation can change whilst angular momentum is conserved it is first best to look at a slightly simpler system - a cat in free fall! Here is a series of photographs taken in $1894$ ...
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  • 77k
32 votes

Why do rotten eggs float in water?

It doesn't need to be rotten. When the egg is getting old, it evaporate water and looses mass while drying. Even if not rotten.
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  • 503
29 votes

How would physics explain why I can't un-fold paper?

When you fold a piece of paper to create a sharp crease, you are permanently damaging the structure of the paper, and that damage (disconnection of bonding between adjacent cellulose fibers and ...
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29 votes

Why does running spend more energy than walking?

This answer may be completely incorrect. See discussion in comments. The formula for power halfway down the page is definitely incorrect. If a moderator would like to delete the answer that would be ...
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  • 8,368
25 votes
Accepted

How can a Kestrel hover in the wind?

A free-body diagram for a fixed-wing airfoil takes into account four interactions: weight, thrust, lift, and drag. For an unpowered airfoil, the thrust is zero. [source] These are approximately ...
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  • 70.1k
25 votes

Direction of water through a pipe

You could probably use ultrasound, as is done for measuring the speed of blood in arteries. I say 'probably' because there mustn't be too large a discrepancy between acoustic impedances of the pipe ...
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  • 27.8k
24 votes

Why does twisting a cork make it easier to remove from a bottle?

As Steeven said, kinetic friction is a smaller force than static friction. Once the cork is moving in any direction, it is easier to move in the direction you want. As Anna V said, bonds may be broken ...
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  • 25.5k
23 votes

Slipstreaming - is there a penalty?

To a certain extent, this depends on the aerodynamic design of the vehicles. But for a simple "boxy" shape, both the lead and trail vehicles could gain an advantage. The rearmost vehicle ...
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  • 33.7k
23 votes

Direction of water through a pipe

A standard technique (https://en.wikipedia.org/wiki/Ultrasonic_flow_meter): Place two ultrasound transducers along the pipe (a few centimetres is OK) and measure the propagation time of signals in ...
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  • 3,574
23 votes

At which slope angle is a runner faster than a bicyclist?

We can at least calculate the angle at which the bike can no longer make progress. In order to maintain any nonnegative vertical velocity, the distance-averaged output force applied by the cyclist to ...
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  • 8,368
23 votes

If I push someone, what fundamental force do I create?

The answers are all conventional, and all misleading. Electromagnetic forces in solid matter are essentially attractive: if you take a solid object and compress it, the electrostatic binding energy ...
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  • 3,239
22 votes

Why do little chips break off so easily from strong neodymium magnets?

The Neodymium magnets that you use are not actually made from solid chunks of metal, but are rather made by compressing a large amount of powder into blocks through a process called sintering. This is ...
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  • 11.1k
22 votes
Accepted

Why do fruits left to dry in the sun feel so much warmer to the touch than other objects outside?

You were on track...and then missed the mark. Higher specific heat means that by the end of the day, the plums have stored more thermal energy than the cardboard box." Correct. You're on track.....
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  • 6,874
22 votes
Accepted

Where does the "water" come from in a mirage?

The reflected image of the palm tree is accompanied by the reflected image of the sky above and surrounding it. so in the reflection, you see the palm tree and the sky. There is no pool of water: the ...
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21 votes

Why does running spend more energy than walking?

On thinking in extremes Many physicists like to think in extremes first. Give you an example, often I can see that some vector is a projection of some other vector, then often my first thought is “...
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  • 34.2k
21 votes
Accepted

Why does water boil in bubbles?

A glass or metal kettle contains many tiny cracks and pits and crevices in its surface which are too small to see but which contain very tiny amounts of air in them. These air-charged pores act as ...
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19 votes

What are the real-life applications of General Relativity?

One wouldn't get very far in many engineering projects without taking gravity into account, and general relativity is our best theory of gravity, so in that sense there are many practical applications ...
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  • 5,808
19 votes
Accepted

Why does the length of a person change when they are lying down or standing up?

It’s because people are squashy. Specifically in this case, it’s the squashy discs between the vertebrae which compress while a person is vertical, but can expand while a person is horizontal. The ...
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  • 70.1k

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