100,000 whys, scientific trivia

Why can radar detect aircraft in night sky?

Radar sends radio waves into air. When an aircraft at high altitude enters an area covered by radar waves, fuselage reflects some of radio waves back. These reflections will reflect on radar screen, indicating that there is an aircraft in sky. Since radio waves are not affected by day and night, radar can detect aircraft in night sky.

Why are submarines free to swim and sink?

Because there are many water tanks on a submarine, and each water tank has inlet and outlet valves. If submarine wants to sink while water tank inlet valve is open, each water tank quickly fills with seawater and weight of submarine increases; when gravity exceeds buoyancy of sea water, it will sink. If you open drain valve and drain water from pressurized tank, weight of submarine will decrease and it will float up. If submersible is submerged in water, some water tanks may be flooded or drained.

Why is there a door at bottom of tank?

The door in bottom of tank is "escape door", because during battle tank can be hit and set on fire, and personnel in tank will have to get out of tank. And if you leave top, it is easy to get injured from enemy guns. Therefore, a door opens in bottom of tank to facilitate escape of tankers and protect life of tankers.

Why should white flag be raised in surrender?

According to law of war, a white flag means a demand for a temporary truce. In ancient times, white flag represented a call for a truce for negotiations. When belligerent side raised white flag, enemy ordered attack to stop. The side holding white flag will send someone to negotiate. The negotiator shall enjoy inviolable rights during period from moment white flag is raised until return of negotiator. After a long period of evolution, white flag gradually became a symbol of surrender.

Why does gas smell bad?

Coal gas is obtained by decomposing coal in a furnace by heating it to 1000 degrees Celsius in absence of air. In past, most of gas cylinders used for cooking at home were gas. Gas can be used not only for cooking, but also as a chemical raw material. However, gas itself is also very dangerous. dizziness. , nausea, vomiting, weakness and even death. In order for this invisible danger to appear, a very smelly mercaptan is added to gas used in everyday life, so that people can find a gas leak in time by smell.

Why can a polygraph tell if a person is lying?

When a person lies, many physiological changes occur, such as increased heart rate and shortness of breath. The lie detector can receive various subtle responses of subject through sensors tied to subject's stomach, fingers, wrists, etc. These response signals are processed into graphs that professionals can view and evaluate whether subject is lying or not, and accuracy is extremely high.

Why does canned food spoil badly?

Black dace in black bean sauce, sardines, beans in tomato sauce, breakfast meat, etc. are all delicious canned foods. Why canned food can be stored for a long time? Because jars are sealed, bacteria cannot get inside. When people make canned food, all air is pumped out of can, and then it is sealed. In absence of air, even small amounts of bacteria on food inside cannot survive or multiply.