Why does the flame only go up and not down when burning?

This is a phenomenon unique to Earth, or a phenomenon on a planet with a similar environment to Earth.

Specifically, gravity and air are needed for flames to burn upwards.

Gravity is the reason for up and down. There is no up and down in the universe. Left and right are determined by human beings' position.

Because the earth has gravity, humans are firmly sucked to the ground, so they feel that underground is down and sky is up.

Our Earth is a planet floating in space. From the perspective of space, there is no up or down.

Due to the gravitational pull of the sun, the earth keeps revolving around the sun. The earth's angular velocity just cancels out the sun's gravitational pull, so it keeps revolving around the sun, unable to escape the sun's gravitational pull, nor being pulled toward it by the sun's gravitational pull.

If we talk about the up and down of the earth, the sun is down and the direction where the earth wants to escape is up.

But we on Earth do not feel this way because we are affected by the Earth’s gravity. Instead, we see the Sun hanging high in the sky, “above”.

But have we ever thought that when the sun sets and reaches the other side of the earth, the sun is under our feet?

If you think in this way, you should understand that up and down are just relative concepts, and they are the feelings we humans have on Earth, right?

If we go into space, where there is no gravity or low gravity, people will float in the spacecraft and there will be no distinction between up and down. Water droplets will not fall, and it will be like a glass marble floating in the air. Fire will certainly not go up, and it will also float in the air in a round shape.

Of course, people may still feel up and down, because the design of the spacecraft is based on human operating habits, and there is a distinction between up and down, front and back. Due to the influence of visual habits, people still think there is up and down. And water droplets and or fire balls will also be a little erratic and swaying because of the air disturbance caused by people inside.

On Earth, there is an atmosphere, and thermal expansion and contraction are the laws of nature. The so-called thermal expansion and contraction is essentially due to the fact that the particles (molecules, atoms) inside the material will increase or decrease in vibration amplitude due to temperature rise or fall. In this way, the higher the temperature, the greater the amplitude of particle vibration, and the material will expand. When the temperature drops, the amplitude of particle vibration decreases, and the object will contract.

Temperature is a physical quantity that indicates the hotness or coldness of an object. In fact, it is a quantitative description of the intensity of the thermal motion of the object's molecules.

When an object of the same mass expands, its volume increases, its density decreases, and it becomes lighter under gravity, so its buoyancy increases, causing hot objects to rise and cold objects to sink. This is the case with air, and fire burns in air, so of course it rises with the hot air.

The atmosphere on Earth flows according to the principle of thermal expansion and contraction and is affected by the tidal force of celestial bodies such as the moon and the sun, forming convection of hot and cold air, which leads to climatic phenomena such as wind, frost, rain, snow, lightning and thunder, enriching our lives and giving life vitality.

The same principle applies to boiling water. Hot water rises and cold water sinks, so the fire can boil the water under the pot or kettle. The boiling phenomenon of water is also the principle of thermal expansion and contraction, and thermal convection.

But some substances also have some special properties. For example, water has the highest density at 4°C. It will expand due to heat above 4°C and expand due to cold below 4°C. This is why a full bottle of water will burst the sealed glass bottle when it freezes.

Some substances, such as antimony, bismuth, gallium and bronze, also have this property.

Flame is a burning gas, which follows the law of thermal expansion and contraction. Combustion is a chemical phenomenon as well as a physical phenomenon. Because ignition must cause a phase change of the substance, that is, the liquid or solid must first be turned into a liquid before combustion can occur, which is a physical change; while combustion is the transformation of a certain substance into another substance, which is a chemical change.

The purpose of ignition is to turn an object into gas. Some substances are easy to evaporate into gas, such as gasoline, which is easy to ignite or even explode; some substances are difficult to turn into gas, such as wood.

When the energy generated by a chemical reaction diffuses outward in the form of heat, it is called an exothermic reaction. The released heat gathers around the reaction area, heating the surrounding air and causing the air molecules to move violently at high speed. The faster the speed, the higher the temperature.

Therefore, the essence of flame is the phenomenon of luminescence caused by the air molecules around the exothermic reaction zone being heated and moving at high speed.

Due to the uneven particle movement speed in different areas of the combustion process, the flame presents different levels, such as flame core, inner flame, and outer flame.

The particles in the flame core move at the slowest speed, followed by the inner flame, and the particles in the outer flame move at the fastest speed. Therefore, the inner flame has the lowest temperature, the outer flame has the highest temperature, and the brightness is also high.

The higher the temperature, the greater the object's coefficient of expansion. Under gravity, it appears lighter, so of course the flame rises.

Summary: The phenomenon of flames pointing upwards on Earth is due to the Earth's gravity and air conditions, and is determined by the property of matter to expand when heated and contract when cooled.

That’s it, welcome to discuss, thanks for reading.

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