Why do cranes and other birds keep in schools during long-distance flights?
Answer. The most powerful bird is ahead. The air flows around it, like water the bow of a ship, a wedge forms behind it, inside which weaker birds experience less air resistance.
A bullet, hitting a boiled egg, pierces it, leaving a hole, and a raw egg is shattered by a bullet. Why?
Answer. A boiled egg (especially the yolk) has a slight elasticity, the pressure in it increases little when the bullet passes. In a raw egg, as in a liquid (elastic medium), the pressure rises instantly and very strongly.
Why is it difficult to clap your hands underwater?
Answer. When they move slowly, little water is carried away by them, and when they move quickly, the water does not have time to “part” (there is an “attached mass”).
Why can moose walk in snow or swamp without getting stuck?
Answer. Elk is a cloven-hoofed animal. There is a membrane between the forked parts of the hooves (when the parts of the hooves move apart, the support area increases, the pressure on the soil, the snow decreases).
Why is it more difficult to pull carrots and other root vegetables out of dense soil than from loose soil?
Answer. Under the root crop, when pulled out, a vacuum is formed (pressure less than atmospheric). The denser the soil, the greater the vacuum.
Why are joint dislocations more common in people high in the mountains than below?
Answer. At altitude, the pressure is lowered, the force of pressing against each other of the bones articulated in the joint becomes less, and dislocations of the joints occur more often.
Why do tea leaves gather in the center of the glass when tea is stirred?
Answer. The higher the speed, the lower the pressure in the moving fluid. The speed is lower near the edges of the glass (due to the friction of the water on the glass). Excessive pressure between the center and the edges of the glass moves the tea leaves towards the center.
Why does a fish need a swim bladder?
Answer. By squeezing and stretching it with muscles, fish regulate the volume, which means the density of their body. Compression – decrease in volume – increase in density – immersion (and vice versa).
Why do freezing people and animals tremble?
Answer. So they get warm. Movements are made – mechanical work is performed – internal energy rises.
On hot days, it is cooler in a deciduous forest than in a coniferous forest. Why?
Answer. Trees evaporate moisture from the leaf surface. At the same time, the internal energy of the leaves decreases (they are cooled) and the air cools. Deciduous trees have more leaf surface area – more evaporation – more cooling.
Why doesn’t a leaning bike fall when cornering?
Answer. For movement in a circle, the action of centripetal force is necessary. It occurs when the bike is tilted.
In the experiment with “Magdeburg plates” Otto Kerike harnessed 8 horses on the left and 8 horses on the right. How could the same number of horses develop more traction?
Answer. Fix one plate, and 16 horses to the other (the force of action is equal to the force of reaction).
Boiling water extinguishes a fire faster than cold water (it immediately takes away the heat of vaporization from the flame and surrounds the fire with a layer of steam, which impedes the access of air).
Is it possible to pump boiling water directly into the flame with pumps?
Answer. Not. In the pump under the piston, instead of the discharged air, there will be steam with an elasticity of 1 atm. Boiling water will not flow into the hoses.
In the pipes of underground parts of buildings, water often freezes not in frost, but in a thaw in spring. Why?
Answer. Thermal conductivity is carried out slowly in the ground (low coefficient of thermal conductivity).
Wood conducts sound better than air. Why is the conversation in the next room muted when the door to the room is closed?
Answer. “At the boundary” of air-wood, sound passes from a medium that is poorly conductive of sound (in comparison with wood) to an environment that conducts sound quickly (wood). There is a limiting angle of incidence for sound beams. Much of the sound waves must be reflected back into the air.
What nationalities were Celsius, Reolif and Fahrenheit?
Answer. Swede, French, German.
Why is intense heat more difficult to tolerate in swampy places than in dry ones?
Answer. In a swampy area, the relative humidity is high, sweat evaporates poorly, and the skin cools slowly.
Drops are falling from the tap of the samovar. When are these droplets heavier: when is the water hot or when is it cold?
Answer. When the water has cooled down, because with decreasing temperature, the surface tension coefficient increases and the drop becomes larger.
How will an electrified stick act on a magnetic needle? Why?
Answer. The end of the arrow will be attracted to the electrified stick, because the induced charges will appear on the steel arrow.
“Rye, rye … Field road
Leads to no one knows where.
Sagging low over the steppe,
The wires groan lazily … ”
Why are the wires buzzing?
Answer. When air flows around the wires, “vortices” are formed behind them. The pressure in vortices is less than where there are none. Whirlwinds “break” from the wires and “sound”.
Why do electrostatic instruments have no sharp ends?
Answer. The charge density is higher where the surface curvature is greater (at the tip). Near the tip, the air is ionized and neutralizes its charge (“charge drains”). To keep the charge, the surface is made round, smooth.
An electrified soap bubble inflates so much that its radius increases significantly (the charge does not change). How will the charge energy change? Does the charge help or hinder the inflation of the bubble?
Answer. The charge energy will decrease (Wp = Q2 / 2R); it is easier to inflate a charged bubble, because the charges repel each other and contribute to an increase in the free surface.
In 1822, Arago noticed that a magnetic needle oscillating around the equilibrium position quickly stops if it is in a copper case. Why?
Answer. The swinging magnetic needle creates an alternating magnetic field. It induces eddy currents in copper, the direction of which is such that they impede the movement of the arrow with their fields.
If you hit one end of a long metal pipe with a hammer, the person at the other end of the pipe will hear a double blow. Why?
Answer. The first blow is a sound wave against metal, the second – in the air.
Water is poured into the bottle. The jet of water produces a noise of a certain tone. As the bottle is filled with water, this tone becomes higher. Why?
Answer. The cavity of the bottle is a resonator. As the bottle fills, the length of the resonator column decreases. The pitch increases.
If you rub the balloon of a neon light bulb, you will notice that it glows for a short time. How can this phenomenon be explained?
Answer. As a result of friction, charges appear on the glass, the field of which causes a short-term glow of the lamp.
How should the two converging lenses be positioned so that the beam of parallel rays, passing through both lenses, becomes parallel again?
Answer. So that their main focuses coincide.
Why do the windows of houses appear dark during the day, i.e. darker than the outside walls, even if they are (walls) painted with dark paint?
Answer. Reflection of light from walls is always greater than reflection from transparent ones, i.e. letting in light, windows.
Lenz Emiliy Khristianovich – Russian physicist. In what area of physics did he carry out his main work? What exactly are his main works related to?
Answer. In the field of electromagnetism. Lenz’s law on the direction of the induction current.
Huygens Christian is a Dutch physicist. In what area of physics is his work known?
Answer. In the field of mechanics, optics. Huygens’ formula for the period of harmonic oscillations of a physical pendulum. Huygens’ principles in explaining the mechanism of light propagation.
Only bullets whistle across the steppe,
Only the wind hums in the wires
The stars twinkle dimly. ”
Why do the stars twinkle?
Answer. The reason is in the properties of the earth’s atmosphere. Now here and there there are clots, then discharges. The pressure is changing too. Air density “jumps” together with pressure. Through such areas, light cannot propagate in a straight line. Light from a star, passing through the earth’s atmosphere, undergoes numerous and erratic deflections. That is why the star flickers.
A negatively charged body is brought to a positively charged electroscope. What happens then?
Answer. First, the angle between the leaves decreases, then = 0, and then increases.
Indicate as many similarities and differences as possible between electric and gravitational fields.
1) analogy of interaction of charges and masses (laws of Coulomb and Newton);
2) both fields are conservative (work on a closed path is zero);
3) the existence of a potential difference in them.
1) there are no negative masses;
2) there are no gravitationally neutral bodies.
Why are powder stores surrounded by a grounded metal mesh?
Answer. There is no electric field inside the metal mesh, no electric spark arises.
Why doesn’t he electrocute a bird that sits on one of the high voltage wires?
Answer. The potential difference between the legs is small, the current is small.
How does the current change in a circuit with a carbon lamp and a lamp with a metal filament immediately after switching on?
Answer. In the second, as the filament heats up, the current decreases (the resistance increases). In coal it is the other way around.
Pieces of copper, iron and nickelin wire of the same diameter and length are included in the current circuit. Which pieces will get hotter:
a) with a serial connection;
b) with parallel?
a) nickelin, iron, copper (as the resistance decreases);
b) copper, iron, nickelin (as the current decreases).
To determine the sign of the poles of the source, the wires connected to the source are lowered into a glass of water and observed near which of the wires more gas is released. How is it determined which pole is negative?
Answer. During electrolysis of water, the volume of released hydrogen is 2 times the volume of oxygen. The negative pole will be the one with more gas (hydrogen, whose ions are positive).
As current flows through the electrolytes, they heat up. Why?
Answer. Ions in electrolytes move at an accelerated rate when current flows. During collisions, the energy (kinetic) of ordered motion is converted into the energy of chaotic (thermal) motion.
How will the breakdown voltage of the gas gap change (increase or decrease) with decreasing gas pressure?
Answer. The lower the pressure, the longer the mean free path, the higher the kinetic energy of the ion accumulates, the higher the probability of ionization at the same (or lower) voltage. The breakdown voltage decreases with decreasing pressure.
Experience shows that it is impossible to charge infinitely any body and that, after the charge on the body reaches a certain maximum value, depending on the size and shape of the body and the properties of the environment, further increase in the charge cannot be achieved. Why?
Answer. With a sufficiently high electric field strength around the body, a discharge (corona or spark) occurs in the surrounding dielectric (air) and the air loses its insulating properties.
An iron cube lying on a smooth glass is attracted to a magnet also lying on this glass. The cube slides on the glass. How does it move (what is the nature of its movement)?
Answer. The force acting on the cube increases as it approaches the magnet. The movement of the cube with increasing acceleration.
Which of the cathode rays are deflected more strongly by the same magnetic field: faster or slower?
Answer. Faster electrons are deflected more (the Lorentz force is directly proportional to the charge velocity of the electrons that make up the cathode rays).
When the current from one or more batteries is closed, a spark does not work, but when it is opened, it does. Why?
Answer. When turned on, the EMF of induction is directed against the EMF of the circuit, and when turned off – in the same direction with it (Lenz’s law).
The pendulum is made of a vessel of water suspended from a long string. The water is gradually poured out through the hole in the bottom of the vessel. How will the period of the pendulum change (we neglect the mass of the vessel)?
Answer. The pendulum can be considered mathematical. Its length will increase. The period will also increase.
Why is there a sharp deafening blow at close lightning, and a rolling thunder at a distant lightning?
Answer. When close, the primary sound wave from the lightning itself is many times stronger than the echo that comes later from reflecting objects. With a distant one, the primary and reflected waves reach us less differing in strength.
Two identical particles, but one fast and the other slow, move in a circle in the same magnetic field. Which of the particles rotates faster?
Answer. The turnover time does not depend on the particle velocity. (m / qBp 2 = t)
The flat mirror is rotated at an angle of 30 degrees about an axis lying in the plane of the mirror and perpendicular to the incident beam. At what angle will the reflected beam turn?
Answer. 60 degrees.
How quickly can you determine the center of gravity of a uniform stick weighted at one end?
Answer. Place it on the index fingers of the left and right hands. Bring your fingers together. They will converge under the center of gravity of the stick.
Where does the steamer sink deeper into the water: in the river or in the sea? Why?
Answer. In a river. The density of salt water is greater than that of fresh water. In the sea of Archimedes, the strength increases.