Since any work must make sense, the interest of the children can be stimulated by the assessment. If the problem was asked at home, then for five different solutions of the problem - score "5", for every two additional solutions - one more score "5". If the task was given in the classroom, then the assessment was given to the most active students.
- Cover the vessel with a lid 2 ... Thus, to increase the pressure, and, consequently, the boiling point of water in it.
- Salt the water in the vessel 2 - the boiling point will also rise.
- Boil water in a vessel 2 several times, letting it cool between boils. Thus, we will remove impurities from the water (they will precipitate), and, consequently, the centers of vaporization, therefore, we will increase the boiling point of water.
- Place on the bottom of the vessel 2 ultrasonic generator.
- Place a copper rod in the water so that it rests against the bottoms of both vessels. In this case, we get a heat conductor.
- Wait until the water is in the vessel. 2 boil away.
- Pour into a vessel 2 liquid boiling at temperatures above 100 ° C.
- Heat the magnet. Thus, we will misorient the domains in the magnet.
- Heat the nail. Thus, we will misorient the domains in
nail.
- Use a lever made of wood or non-magnetic metal.
- Wind the wire around the nail and let the current flow. Thus, turn the nail into a magnet of the same polarity with the ends of the horseshoe.
- Pull the nail sharply.
- Place the iron bar above the nail. Thus, we "short-circuit" the lines of magnetic induction and weaken the magnetic field at the ends of the magnet.
- Knock on the magnet. Deformation will lead to disruption of the ordered orientation of the domains in the magnet.
- Pump air into the flask. As you know, the arch is easy to break if you push from the inside.
- Place the entire system under the bell, plugging the tube, and evacuate the air from the bell. Thus, we will create excess pressure in the flask, and it will burst, as in the previous case.
- Pour water into a flask and freeze. The flask will burst, because the water expands upon cooling.
- Heat the flask unevenly. Cool half of the flask, and heat the second. The flask will crack due to the difference in thermal expansion.
- Send a sound wave to the flask. The sound will cause the walls of the flask to oscillate, and at resonance the flask will burst.
- Put some more bricks on top.
- Hit the brick.
- Wait for the water to evaporate.
- Heat the mug to speed up the evaporation.
- Put a spoon in a mug and freeze. Then take out a spoon along with ice.
Note... Immediately after freezing, the spoon cannot be reached, so the edges of the mug will need to be slightly heated.
- Dip a sponge into the glass.
- Place the cocktail tube in the mug and suck out the water.
- Put the end of the long rubber tube into the mug, lower its other end below the level of the liquid surface and suck the air out of the tube - water will flow out.
- Place the tube in the mug, the other end of which is placed in a vessel with low pressure. Atmospheric pressure will force the water into another vessel.
- Move the glasses relative to each other, turning one relative to the other.
- Wait a while. The system is not completely sealed and air still leaks through the gasket.
- Increase the temperature of the glasses, for example, pour boiling water over them. The gas pressure in the glasses will rise.
- Place the system under the bell and evacuate the air. The pressure in the glasses will be greater than outside.
How to divide an ice cube into two equal parts?
- Saw.
- Grind into crumbs and divide.
- Cut with a hot knife.
- Heat half.
- Melt the cube, divide the water in half, freeze the resulting halves.
- Place a support.
- Nail the legs to the floor.
- Experimentally select the angle of inclination so that equilibrium is established. Trim the chair legs at this angle to increase the footprint.
- Cut out recesses in the floor at an angle and insert the legs of the chair into them.
- Glue the chair.
How to make a mathematical matrix swing in only one plane?
- Spin the load around its axis. As a result, we get a gyroscope, and, as you know, the plane of rotation of the gyroscope does not change its position in space.
- Make an iron weight swing in a magnetic field.
- Construct a guiding structure (two plates).
- Make a metal weight swing in a static electric field (for example, between two charged balls).
- Fine tune at startup.
How to chill the water in the bottle?
- Put the bottle in the refrigerator.
- Put (on) under ice.
- Wrap the bottle with a damp cloth and place in a stream of air. When water evaporates from the surface of the rag, the latter will cool, taking heat away from the water bottle.
- Wrap the bottle with a damp cloth, place it under the bell and evacuate the air. Thus, we will lower the pressure, therefore, we will accelerate the evaporation.
- Place the bottle in a container with colder water, such as ice.
- Chemically cool.
How to connect two metal plates?
- Use a bolt and nut.
- Use rivets.
- Glue.
- Solder.
- Cook. (Not all metals are welded - Ed.)
- Use electric spot welding.
- Grind and grind both surfaces to be joined and press firmly. (This is how cold welding is carried out in space. Ed.)
How to heat up a metal ball?
- Put in the oven.
- Hit.
- Rub for a long time.
- Deform.
- Pass the electric current.
How to speed up the drying of a damp cloth?
- Hang on a rope in a dry warm room.
- Expand it as much as possible.
- Place in a dry air stream.
- Place between dry rags (newspapers) and change them periodically.
- Sprinkle a cloth with dry sand (sawdust), periodically shake it off and sprinkle again with a new portion of sand. The sand absorbs moisture.
- Place it near a powerful source of high frequency electromagnetic radiation. As a result of the action of Foucault currents, the liquid will be heated.
How to remove excess stone?
- Chip off with a chisel and hammer.
- Erase.
- Heat the stone and cool it sharply. As a result of the sharp temperature drop due to thermal expansion, the stone will crack.
- Cool and heat rapidly.
- Cut off.
- To melt.
What's the fastest way to fill a bucket in the rain?
- Place a bucket under the drain near the roof of the house. There, water is collected from a large roof surface.
- Place the funnel over the bucket.
- Put a cloth of fabric into the bucket with one end, and hang the other end. The water will drain from the fabric into the bucket (the area from which water is collected will increase)
- Place the bucket at an angle of 45 ° to the direction of the droplets falling. (It will be worse. - Ed.)
- Place several charges of the same name in the center of the bucket. As a result, the trajectory of the droplets will change.
How to raise the water level in the elbow of a U-tube relative to the other?
- Pump out air from one knee and close this knee with a stopper.
- Pump air into one knee and close this knee with a stopper.
- Pour a lighter liquid (eg kerosene) into one elbow.
- Place the baffle (piston) between the knees and move it, for example, on a thread.
- Use the phenomenon of osmosis.
How to make a car rolling off a hump to travel a greater distance by inertia?
- Nudge.
- Load the car.
- Lubricate the rails with oil, thereby reducing the coefficient of friction.
- Cool the rails. There is always water vapor in the atmosphere, condensation will appear on the cooled rails, which will reduce friction.
How to ensure the presence of water molecules at a height of 1 cm above the surface of the water in the vessel?
- Dip the wick into the water. Water molecules will rise through the capillaries.
- Throw ice into the water: it floats in the water, therefore, you can pick up a piece that will rise 1 cm above the surface, and ice is also water.
- Lower the sponge. The water, as in the case of the wick, will rise.
- Heat the water.
- Nothing to do. Water evaporates at any temperature, therefore, above the surface, at any or almost any height, there is at least one H2O molecule.
How to light up a small space?
- Light a match (candle, torch).
- Light it up with a flashlight.
- Ignite an electrical discharge.
- Excite luminescence.
- Excite the Cherenkov glow (the glow of water when particles pass through it at a speed higher than the speed of light in water).
How to speed up the boiling of liquid in a kettle?
- Increase the power of the heater.
- Pour not water into the kettle, but a more easily boiling liquid (for example, acetone).
- Insulate the kettle, for example, wrap it in a thick cloth and a cotton blanket.
- Place the kettle in a low pressure area.
- Constantly knock on the kettle, thereby stirring the water.
How to stop a spring watch without damaging its outer shell?
- Do not touch the watch for a long time - they will stop themselves.
- Strongly shake, drop, hit.
- Dip in liquid and freeze.
- Place in liquid nitrogen.
- Place in an alternating magnetic field.
- Heat.
How to improve the glide of boots on ice?
Answer options
- Completely wipe off the outsole protector.
- Make the ice even, smooth.
- Make the ice surface moist.
- Pour oil over the ice.
- Attach runners to the boots (to make skates).
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4th year student of VyatSUH, gave this material in 2005 in the classroom and extracurricular activities, passing pedagogical practice at school number 5 (Slobodskoy, Kirov region, head - Honored teacher of the Russian Federation Victor Ivanovich Elkin [email protected]). The students really liked the problems, they solved them with pleasure.
The downwind movement of a sailing yacht is actually determined by the simple wind pressure on its sail, pushing the boat forward. However, wind tunnel studies have shown that sailing upwind exposes the sail to a more complex set of forces.
When the incoming air flows around the concave rear surface of the sail, the air speed decreases, while when flowing around the convex front surface of the sail, this speed increases. As a result, an area of increased pressure is formed on the rear surface of the sail, and a low pressure area on the front surface. The pressure difference on the two sides of the sail creates a pulling (pushing) force that moves the yacht forward at an angle to the wind.
A sailing yacht, located approximately at right angles to the wind (in nautical terminology, a yacht is tacking), moves quickly forward. The sail is subjected to pulling and lateral forces. If a sailing yacht goes at an acute angle to the wind, its speed slows down due to a decrease in pulling force and an increase in lateral. The more the sail is turned towards the stern, the slower the yacht moves forward, in particular due to the large lateral force.
A sailing yacht cannot sail straight upwind, but it can propel itself forward in a series of short zigzag moves at an angle to the wind, called tacks. If the wind blows to the port side (1), the yacht is said to be sailing on the port tack, if to the starboard side (2) - on the starboard tack. In order to go faster the distance, the yachtsman tries to increase the speed of the boat to the limit by adjusting the position of her sail, as shown in the figure below on the left. To minimize deviation from the straight line, the yacht moves, changing course from starboard to port and vice versa. When the yacht changes course, the sail is thrown to the other side, and when its plane coincides with the wind line, it rushes for some time, i.e. is inactive (middle figure below the text). The yacht falls into the so-called dead zone, losing speed until the wind again inflates the sail from the opposite side.
The winds that are in the southern part The Pacific blowing westward. That is why our route was designed so that the sailing yacht "Juliet" moves from east to west, that is, so that the wind blows in the back.
However, if you look at our route, you will notice that often, for example, when moving from south to north from Samoa to Tokelau, we had to move perpendicular to the wind. And sometimes the direction of the wind changed altogether and had to go against the wind.
Juliet Route
What to do in this case?
Sailing ships have long been able to sail against the wind. The classic Yakov Perelman wrote about this for a long time well and simply in his Second book from the Entertaining Physics cycle. I am citing this piece here verbatim with pictures.
"Sailing against the wind
It is difficult to imagine how sailing ships can go "against the wind" - or, in the words of the sailors, go "to the sidewind". True, the sailor will tell you that you cannot go directly against the wind under sails, but you can only move at an acute angle to the direction of the wind. But this angle is small - about a quarter of the right angle - and it seems, perhaps, equally incomprehensible: whether to sail directly against the wind or at an angle of 22 ° to it.
In practice, however, this is not indifferent, and we will now explain how the force of the wind can go towards it at a slight angle. First, let's consider how the wind acts on the sail in general, i.e. where it pushes the sail when it blows on it. You probably think that the wind always pushes the sail in the direction it is blowing. But this is not so: wherever the wind blows, it pushes the sail perpendicular to the plane of the sail. Indeed: let the wind blow in the direction indicated by the arrows in the figure below; line AB represents the sail.
The wind always pushes the sail at right angles to its plane.
Since the wind presses evenly on the entire surface of the sail, we replace the wind pressure with the force R applied to the middle of the sail. We decompose this force into two: the force Q, perpendicular to the sail, and the force P, directed along it (see the figure above, on the right). The last force pushes the sail nowhere, since the friction of the wind against the canvas is negligible. The force Q remains, which pushes the sail at right angles to it.
Knowing this, we can easily understand how a sailing vessel can go at an acute angle towards the wind. Let the KK line represent the keel line of the vessel.
How can you sail against the wind.
The wind is blowing at an acute angle to this line in the direction indicated by the row of arrows. Line AB represents the sail; it is placed so that its plane bisects the angle between the direction of the keel and the direction of the wind. Follow the decomposition of forces in the figure. We represent the wind pressure on the sail by the force Q, which, we know, must be perpendicular to the sail. We decompose this force into two: the force R, perpendicular to the keel, and the force S, directed forward, along the keel line of the vessel. Since the movement of the ship in the direction of R meets strong water resistance (the keel in sailing ships becomes very deep), the force of R is almost completely balanced by the resistance of the water. Only the force S remains, which, as you can see, is directed forward and, therefore, moves the ship at an angle, as if towards the wind. [It can be argued that S is most significant when the sail plane halves the angle between the keel and wind directions.]. Typically, this movement is performed in zigzags, as shown in the figure below. In the language of sailors, this movement of the ship is called "tacking" in the narrow sense of the word. "
Let's now consider all the possible wind directions relative to the boat's course.
The diagram of the ship's course relative to the wind, that is, the angle between the direction of the wind and the vector from stern to bow (heading). 
When the wind blows in the face (leventik), the sails dangle from side to side and it is impossible to move with the sail. Of course, you can always lower the sails and turn on the motor, but this has nothing to do with sailing.
When the wind blows exactly in the back (forewind, tailwind), the dispersed air molecules put pressure on the sail from one side and the boat moves. In this case, the vessel can only move slower than the wind speed. The analogy of cycling in the wind works here - the wind blows in the back and it is easier to pedal.
When moving against the wind (beydewind), the sail moves not because of the pressure of air molecules on the sail from behind, as in the case of fordewind, but because of the lift that is created due to different air velocities from both sides along the sail. At the same time, due to the keel, the boat moves not in the direction perpendicular to the boat's course, but only forward. That is, the sail in this case is not an umbrella, as in the case of a side haul, but an airplane wing.
During our crossings, we mainly walked backstays and gulfwinds at an average speed of 7-8 knots with a wind speed of 15 knots. Sometimes we went against the wind, Gulfwind and Beydewind. And when the wind died down, they turned on the motor.
In general, a boat with a sail going against the wind is not a miracle, but a reality.
The most interesting thing is that boats can walk not only against the wind, but even faster than the wind. This happens when the boat is backstaying, creating "its own wind".
I think that many of us would take the chance to dive into the sea abyss in some kind of underwater vehicle, but still, most would prefer a sea voyage on a sailboat. When there were no planes or trains, there were only sailboats. The world was without them, did not become like this.
Sailboats with straight sails brought Europeans to America. Their stable decks and roomy holds brought men and supplies to build the New World. But even these ancient ships had their limitations. They walked slowly and practically in the same direction downwind. Much has changed since then. Today they use completely different principles of wind and wave power management. So if you want to ride a modern one, you will have to learn some physics.
Modern sailing it is not just movement in the wind, it is something that affects the sail and makes it fly like a wing. And this invisible "something" is called lift, which scientists call lateral force.
An attentive observer could not help but notice that no matter where the wind blows, the sailing yacht always moves where the captain needs it - even when the wind is head-on. What is the secret of such an amazing combination of stubbornness and obedience.
Many do not even realize that a sail is a wing, and the principle of operation of a wing and a sail is the same. It is based on lift only if the lift of the wing aircraft, using the headwind, pushes the plane up, then the vertically located sail directs the sailboat forward. To explain this scientifically, you need to go back to the basics - how the sail works.
Take a look at the simulated process that shows how air acts on the plane of the sail. Here you can see that the more curved air currents beneath the model bend to bypass the model. In this case, the flow has to speed up a little. The result is a low-pressure area - this generates lift. Low pressure on the underside pulls the sail down.
In other words, the high pressure area tries to move towards the low pressure area, putting pressure on the sail. A pressure difference arises, which generates a lifting force. Due to the shape of the sail, on the inner windward side, the wind speed is less than on the leeward side. A vacuum is formed on the outside. The sail literally sucks in air, which pushes the sailing yacht forward.
In fact, this principle is quite simple to understand, just take a closer look at any sailing vessel. The trick here is that the sail, no matter how it is located, transmits wind energy to the ship, and even if it visually seems that the sail should slow down the yacht, the center of application of forces is closer to the bow of the sailboat, and the wind force provides translational movement.
But this is theory, but in practice everything is a little different. In fact, a sailing yacht cannot go against the wind - it moves at a certain angle to it, the so-called tacks.
The sailboat moves due to the balance of forces. Sails act like wings. Most of the lift they generate is directed to the side, and only a small amount to the front. However, the secret is in this wonderful phenomenon in the so-called "invisible" sail, which is located under the bottom of the yacht. Is it keel or on nautical language- centerboard. The lift of the centerboard also produces lift, which is also directed primarily to the side. The keel is opposed to heel and the opposite force on the sail.
In addition to the lifting force, there is also a roll - a phenomenon harmful to forward movement and dangerous for the ship's crew. But this is why there is a team on the yacht to serve as a living counterbalance to the inexorable physical laws.
In a modern sailboat, both the keel and the sail work together to steer the sailboat forward. But as any novice sailor will confirm in practice, everything is much more complicated than in theory. A seasoned sailor knows that even the slightest change in the sail's bend makes it possible to gain more lift and control its direction. By varying the curvature of the sail, the skilled sailor controls the size and position of the lift-producing area. A deep forward bend can create a large pressure zone, but if the bend is too large or the leading edge is too steep, the air molecules around it will no longer follow the bend. In other words, if the object has sharp corners of the flow particles cannot make a turn - the impulse of motion is too strong, this phenomenon is called "separated flow". The result of this effect is that the sail will "flatter", losing wind.
And here are a few more practical advice use of wind energy. Optimal headwind course (racing sidewind). Sailors call it "running against the wind." Pennant wind, which has a speed of 17 knots, is noticeably faster than the true wind, which creates a wave system. The difference in their directions is 12 °. Heading to apparent wind - 33 °, to true wind - 45 °.
Russian poet Mikhail Yurievich Lermontov loved sea and in his works he often mentioned him. He wrote a wonderful poem about the whitening sail, which rushes among the waves in the distant sea. You are probably familiar with Lermontov's poem, because these are the most famous poetic lines about sailing ships. Reading them, one can imagine a raging sea and beautiful ships among its waves. The wind blows the sails. And, thanks to the force of the wind, the ships move forward. But how do sailboats manage to sail against the wind?
In order to answer this, you first have to learn an unfamiliar word. "tack".Halsom is the direction of movement of the vessel relative to the wind. The tack can be left when the wind is blowing from the left, or right when the wind is blowing from the right. It is also important to know the second meaning of the word "tack" - this is a part of the path, or rather, its section that a sailboat passes when it moves against the wind... Remember?
Now, in order to understand how sailboats manage to sail against the wind, let's deal with the sails. They come in different shapes and sizes on a sailboat - straight and oblique... And everyone is doing their job. When a headwind blows, the ship is steered by oblique sails that turn one way or the other.
Following them, the ship turns in one direction or the other. Turns and walks forward. The sailors call this movement - variable tack... Its essence lies in the fact that the wind presses on the oblique sails and blows the ship slightly sideways and forward. The rudder of the sailboat does not allow it to turn completely, and the skilled sailors set the sails in motion in time, changing their position. So, in small zigzags, and moves forward.
Of course, variable tacking is very difficult for the entire crew of a sailboat. But the sailors are seasoned guys. They are not afraid of difficulties and are very fond of the sea.
