Physics mysteries

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What does a heat pump need electricity for?

Edita Bromova

A heat pump is said to be a miraculous machine that will heat my home from heat collected somewhere outside. But now I found out that it needs electricity to operate ...
A heat pump is actually a bit like a refrigerator. While a fridge takes heat from its interior and heats the room in which it stands, a heat pump takes heat from the external heat reservoir to heat the interior of the house. A suitable reservoir can be the surrounding air, the ground on which the house stands or a water tank ...
(Source: stock.adobe.com)

How small can a nuclear reactor be?

Edita Bromova

Nuclear reactors in nuclear power plants are quite large. But how much fissionable uranium do we need, so that a controlled reaction can take place in it and produce heat? Can we build a nuclear react ...
The smallest amount of fissile material in which a fission chain reaction can take place is called the critical amount. Most of the neutrons produced in it during fission continue to participate in fission. This allows the reaction to run continuously. The critical amount depends on the type of fissile material, its concentration and the shape in which it is arranged ...
(Source: stock.adobe.com)

Can radioactivity be seen?

Edita Bromova

It is said that radioactivity cannot be seen, heard or felt. But isn't there the possibility that we could see it under certain circumstances? Aren't there any animals, whose senses would allow them t ...
Ionizing radiation is all around us. It arises from the decay of atoms in our surroundings and in our own bodies or it comes to us from space as cosmic radiation. We call materials containing unstable isotopes radioactive, but since everything around us is slightly radioactive, we have not developed senses to detect radioactivity ...

Why do I tan more in winter than in summer?

Jaroslav Kores, Ph.D.

To be honest, I haven’t experienced this but it’s probably because I don’t sunbathe much. I don’t know if the winter tan is also related to the skiing/mountain activities. If this is indeed the case, I think it has two causes ...

Why can’t you make a fire using a magnifying glass and some “special” flashlight or moonlight?

Jaroslav Kores, Ph.D.

It would certainly be possible but we would need either a better flashlight or a bigger magnifying glass. About 1,000 W/m2 of energy reaches the Earth from the Sun. If the Moon reflects roughly 20% of the falling sunlight, we would need a 5x better magnifier (i.e. a magnifier with a 5x larger surface, i.e. a 2.3x larger radius) ...

According to what pattern do sunrises, sunsets, moonrises and moonsets change?

Jaroslav Kores, Ph.D.

The movements of bodies in the central gravitational field are described by Kepler's laws, of which only law 3 has the form of a formula. Isaac Newton used Kepler’s laws to formulate (his) law of gravity ...

Can someone break a glass or any object with their voice (sound made)?

Jaroslav Kores, Ph.D.

Everything can be broken, the only question is how difficult it will be. It will be simple in theory with a glass but I personally wouldn’t trust the implementation, especially due to the absence of a musical ear? When we tap the glass, we can hear a sound. The pitch (frequency) of this sound depends on the material and shape of the glass ...

Why can engine performance be determined by “horsepower”? Is it some kind of conversion to real horses? What kind?

Jaroslav Kores, Ph.D.

Horse power was introduced by James Watt to be able to approximate the power of the steam engine. Simply put, by determining the horsepower of a horse and comparing it to a steam engine, he could say: “My steam engine will replace 10 horses”. This way it was easy for everyone to imagine and was certainly well thought out in terms of marketing ...

Why is the selfie photo rotated horizontally?

Jaroslav Kores, Ph.D.

All photos are basically rotated, more precisely inverted. This is because the display system of the camera/mobile phone has to create an actual image on the sensor. If we want to use a lens/mirror to create a real image, it will always be inverted. In the same way, the lens in our eye creates an inverted image on the retina and the brain “turns” it around ...

What food is the most radioactive?

Jaroslav Kores, Ph.D.

I believe that the content of radioactive substances in food depends mainly on where we get the food from. Radioactive materials enter food from its surroundings. Plants and mushrooms get radioactivity from the soil they grow in and animals have radioactive particles in them either from food (plants) or air/water ...

What happens to lightning (energy) when it goes down a lightning rod to the ground?

Jaroslav Kores, Ph.D.

In general, energy that we can’t use turns into heat and that’s what happens with lightning energy. It is necessary to realize that lightning is actually a slightly stronger example of an electric current (we call it an electric discharge) and therefore the same applies to it as, for example, to an electric kettle, a light bulb or a washing machine ...

Why is the colour of photos of the countryside different in the morning and in the evening (the sun has a similar angle)?

Jaroslav Kores, Ph.D.

I don’t think that there would always be a difference between the photos in the morning and in the evening, I would rather expect that we can observe something similar from time to time. And I would guess especially in the summer ...

Does the force required to lift a stone in water vary with depth? E.g. Can I lift 100 kg at a depth of 1 m, 200 kg at a depth of 10 m?

Jaroslav Kores, Ph.D.

Gravitational force acts on every body. If we want to lift a body, we must exert a greater force in the opposite direction. Buoyant force helps us in water — it has an upward direction and therefore if we want to lift a body in water, the sum of our buoyant force and our force must be greater than the force of gravity ...

Why don’t we see icy (blueish) and hot (reddish) air in different colours?

Jaroslav Kores, Ph.D.

You may work on the assumption of infrared photos — they show the cool bodies in blue and the warmer ones in red. But this colour display is just a visualization of the temperature — the thermometer measures the values and then displays them in different colours on the display ...

Why does a tsunami wave only go in one direction and not in all directions?

Jaroslav Kores, Ph.D.

A tsunami wave, like other waves, spreads in all directions but the effects of a tsunami are observed only in certain places, so it may seem that the tsunami wave is moving in only one direction. Tsunami waves are caused by an underwater earthquake and the energy released by it is used to move a large mass of water ...

Why is it not possible to effectively predict earthquakes?

Jaroslav Kores, Ph.D.

An earthquake is caused by a sudden release of mechanical stress between (or within) lithospheric plates. I’m not a geologist, but I believe this stress is caused by temperature differences and other phenomena that occur in and beneath these plates ...

Why does heat go up and cold air go down?

Jaroslav Kores, Ph.D.

It is the same as why iron sinks to the bottom in water but wood rises. We probably all intuitively know that bodies with a high density in water sink to the bottom and bodies with a low density rise to the top. And perhaps we also know that if a body has the same density as water, it will stay in the given place — it will neither rise nor sink ...

Do mushrooms really contain heavy metals?

Jaroslav Kores, Ph.D.

Yes, mushrooms, like other plants, contain elements that they draw into themselves from the surrounding soil. Compared to other plants, however, mushrooms can absorb a greater number of different elements ...

Is the same person’s weight different at the equator and at the North Pole?

Jaroslav Kores, Ph.D.

I don’t want to be a quibbler but with this question, it is clear that it is good to use the right terms for what we want to find out. Because I could easily answer yes or no, and in both cases I would be right ...

How are high tide and low tide created and why are they needed or important on the Earth?

Jaroslav Kores, Ph.D.

The high tide and associated low tide are caused by the gravitational force acted by the Earth and the Moon on each other. Thanks to this force, the Moon orbits around us and does not fly away. This gravitational effect is also responsible for the fact that the Moon does not rotate on its axis, so that it always faces us on the same side ...
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