You are so good at playing, why don’t you go to the sky? I will go to the sky right now to show you!

Children cannot live without toys. Good toys can not only make children happy, but also arouse their curiosity and thinking about the world. These qualities are of great benefit to their future development. Moreover, although children's toys are relatively simple, the principles used in many toys can actually be used in space!

Today is Children's Day again. Let's take stock and see the principles behind these familiar little toys.

Tin Frog/Pull Back Car/Music Box

We all played with wind-up tin frogs when we were little... What? You haven't played with it? That must be because you experienced a generation gap when tin frogs were outdated and Taobao was not yet popular. Now go to Taobao and find your lost childhood. In addition to the little frog, pull-back cars and music boxes also use wind-up.

Tin frog, picture taken from e-commerce platform

When we wind the spring, the kinetic energy in our hands is transferred to the spring and stored in the spring as elastic potential energy. When we release our hands, the spring slowly stretches, converting the elastic potential energy back into kinetic energy, making the tin frog croak and jump forward, the pull-back car rush to the finish line, and the drum of the music box pluck the strings to play beautiful music. In the adult world, the conversion of elastic potential energy and kinetic energy can also be used for other things.

For example, since ancient times, people all over the world have invented bows and arrows, using elastic potential energy to hunt and fight. Now, people put springs in mechanical watches to drive the pointers, or put them in tape measures or vacuum cleaners to help quickly retract tape measures or cables. Old sofas are filled with springs, and cars and many large precision equipment use springs or hydraulic devices to absorb motion energy to achieve shock absorption. The spring scale is a must-have experimental equipment for middle school physics classes. Even in the vegetable market, you can often see old men and women holding spring scales.

So what does this have to do with space? Of course, we can't use a bow and arrow or a slingshot to blast a spacecraft directly into space. One of the uses of this principle in space is to help astronauts weigh themselves.

You might say: That's not right? The space station is in a microgravity environment, so a spring scale can't be used to weigh it. At this time, Newton's second law comes to help: the astronaut fixes himself to one end of the stretched spring. When the spring returns to its original position, the astronaut's rebound acceleration is measured at the same time, and the astronaut's weight can be calculated.

Wang Yaping is helping Nie Haisheng weigh himself, screenshot from CCTV General Channel

Spinning Top/Diabolo

The toy top is called differently in different parts of the country. Some places call it "bingga", some call it "da laoniu", "lazy woman", "geluo" or "dielou" (I don't know what the specific characters are). The name that impressed me the most is "cha han traitor", which means to whip the traitor so hard that he spins in circles. The top is usually small, and a big person will be unable to straighten up after playing with it for a while. Diabolo is suitable for older children and old children. With two sticks and a rope, you can play many different things. I once heard an expert say, "Give me a pot lid, and I can shake it for you."

Diabolo, captured from an e-commerce platform

Whether it is a spinning top or a diabolo, the common feature is that they can rotate steadily. Why can they rotate steadily? The principle behind it is the conservation of angular momentum. Angular momentum is a physical quantity that measures the rotation of an object, and its direction and size will not change easily. Friends who have played with fidget spinners know that after the spinning top starts to spin, if you change its direction, you can feel its strong "struggle and resistance." Using the law of conservation of angular momentum, people carve rifling (also called rifling) on ​​the barrel of guns and cannons to make the bullet rotate around the axis, so that when it flies to the target, the bullet nose will always face forward and will not roll in the air, so that it can fly as far as possible.

Players who have played the single-wheel diabolo (including the pot lid mentioned by the old man above) also know that after the single-wheel diabolo falls on the rope, it will rotate on its own while rotating around the player. This phenomenon is called "precession" , which is the result of the conserved angular momentum being "twisted" by the earth's gravity and then "dumped", but its "dumping" is in the sideways precession, rather than plunging straight to the ground. By sensing this "precession", the device equipped with a gyroscope can know that the direction of its movement has been twisted. This device is called a "gyroscope" , which is an important attitude control device required for aircraft, satellites, space telescopes, and space stations.

By the way, aside from those high-end precision instruments, the gyro himself has been to space...

Gyroscope movement demonstration, from CCTV News Channel

Bamboo Dragonfly/Water Rocket

The bamboo dragonfly is a traditional Chinese children's toy. It is also very simple to make. A bamboo piece is cut into a windward slope at both ends, and a small wooden stick is inserted in the middle. It can fly into the sky by rubbing it with both hands. The physical principle that supports the bamboo dragonfly is Newton's third law. When the bamboo dragonfly rotates, the slope of the blade pushes the air downward. According to Newton's third law, there must be a reaction force with equal magnitude and opposite direction, acting on the same straight line, so the air pushes the bamboo dragonfly upward. In the adult world, the bamboo dragonfly becomes an airplane, including helicopters and fixed-wing aircraft.

The ultimate supporting principle behind it is to push/throw the air downward more effectively, thereby generating a strong lifting force on the wing/rotor. Newton's third law also created another advanced toy, the water rocket, which many friends have made by hand in physics class. When you pump air into a sealed Coke bottle and suddenly push open the nozzle, the compressed air pushes the water in the bottle downward, and under the push of the reaction force, the water rocket soars up (water rockets are also dangerous, so everyone must pay attention to safety).

Two-stage water rocket, captured from an e-commerce platform

The principle of water rockets and real space rockets is not much different, only the propellant is different. In other aspects, even "the propellant itself is a burden and needs to be carefully calculated", they are the same.

Soap Bubbles

When we were kids and played with bubbles, we must have been fascinated by the color on the bubbles. How is it formed? Is it the color of soapy water? Why do bubbles burst as soon as the color disappears? The secret behind the color of soap bubbles is the wave nature of light. Although we usually say that sunlight is white light, there is actually no "white light". Sunlight is composed of many colors (frequencies) of light, and different colors of light have different wavelengths.

When the same light wave is reflected from the inner and outer walls of a soap bubble, two light waves are generated. If the two light waves are exactly peak to peak and trough to trough, the colors will be enhanced. If the peaks are opposite to troughs and troughs are opposite to peaks, the colors will cancel out. In this way, which color will be enhanced and which color will cancel out is determined by the thickness of the water film of the bubble and our observation angle. This phenomenon is called "interference" and the stripes produced are called interference stripes.

Under the action of gravity, the water in the soap bubbles will slowly flow down along the periphery.

When the water film of the bubble is thin enough, its inner and outer walls cannot cause significant interference effects on any color. Therefore, when we see the soap bubble fade, we know that it is not far from collapse. Using the interference effect, scientists have created many scientific observation equipment, many of which are designed to help us explore the mysteries of the universe. Some equipment has made great achievements in the history of physics development, such as the Michelson-Morley interference experiment, which directly denied the ether, the previously assumed transmission medium of light. Some equipment is so large and invisible that we cannot feel its existence even when we are in it. For example, the famous Event Horizon Telescope, which consists of several radio telescopes scattered around the world, uses the "very long baseline interferometry" technology to capture images of two supermassive black holes.

Puff Boat

In the movie "Ponyo on the Cliff", we see an interesting toy boat, the "Pu-Pu Boat" that Sosuke and Ponyo ride on. Light a candle (magnified by magic) and put it under a small boiler, and the boat will puff forward. In the real world, such a boat can really be built!

Cut the aluminum foil of a can into a small flat bag, insert two straws (two straws are for the convenience of filling with water in the subsequent steps), use glue to seal the gap between the aluminum bag and the straws, inject some water from the straws, prepare a small paper boat with a candle inserted, place the aluminum bag above the candle flame, place the straws in the water, and you can see the boat moving forward!

The engine that drives the Puffboat is called a "Stirling engine" in the heat engine principle. It drives the engine to do work by allowing the gas/liquid in the confined space to oscillate and flow between the hot zone and the cold zone. The Stirling engine is an external combustion engine that is heated from the outside. Compared with the internal combustion engine we are more familiar with (for example, a car engine is an internal combustion engine that burns gasoline in the cylinder), its biggest feature is that it is not limited to heat sources. Whether you generate heat through friction, burning wood, electricity, solar energy, or nuclear reaction, as long as it can generate heat, it can serve as a heat source for the hot zone. In this way, Stirling engines can be used in space! Of course, if Stirling engines are used in space, there are still some details that need to be overcome, such as lubricating oil problems.

Here is a low-key piece of good news. Among the in-orbit tests completed by Shenzhou XV, one was the "Space High-Efficiency Free-Piston Stirling Thermoelectric Conversion Test", which has broad application prospects in future manned lunar and deep space exploration missions.

Finally, I would like to emphasize that although this article is organized in the order of "toys-theory-space", it does not mean that the theories used to build big things are all derived from toys . On the contrary, many times, people first send rockets into space, and then engineers with childlike innocence begin to think about what kind of toys they can make using this principle...

Planning and production

Author: Qu Jiong Communication Technology Engineer

Review丨Liu Yong, Researcher, National Space Science Center, Chinese Academy of Sciences

Planning丨Ding Zong

Editor: Ding Zong

Proofread by Xu Lailinlin