Why does a flame not "fall" under the action of gravity? What happens to flames under weightlessness?

Tech 2023-05-04 22:42:40 Source: Network

We know that all objects on Earth are subjected to the action of gravity. If there were no gravity, the entire Earth would be in chaos

We know that all objects on Earth are subjected to the action of gravity. If there were no gravity, the entire Earth would be in chaos.

But there is something that doesn't seem to be affected by gravity, it always floats in place and even rises. What is this kind of thing?

The answer is flames.

The burning flame does seem to have no weight, because we have never seen it "fall" before. Why is this?

Gravity - the Earth's "ball holding" force

In 1687, British physicist Newton published "Mathematical Principles of Natural Philosophy", in which he elaborated on the law of universal gravitation.

The law of universal gravitation states that there is mutual attraction between any object, and the magnitude of this force is proportional to their mass and inversely proportional to the square of their distance.

The figure is: Schematic diagram of universal gravitation

The law of universal gravitation has also become Newton's first law and is one of the most important laws in the field of natural sciences. Its discovery also laid the foundation for the emergence of celestial mechanics.

We, who live on the surface of the Earth, also have universal gravitation with the Earth, which is mainly manifested in the well-known form of gravity.

But gravity is not completely equal to universal gravitation. This is because the earth rotates with us. When it rotates, it needs centripetal force. Where does centripetal force come from? It can only be served by a portion of the gravitational force.

Therefore, for objects on the earth, gravity is actually the combined force of gravity and centripetal force. It is only because the centripetal force is too small that it is ignored.

Due to the presence of gravity, all objects on Earth can remain stable on the surface of the Earth without drifting, and the thrown objects can return to the ground.

What is burning about? Is flame a substance or a phenomenon?

Combustion is a rapid process of releasing heat, which essentially involves the rapid release of chemical energy into thermal and radiation energy during the redox reaction between combustible materials and oxidants.

According to the method of energy transfer, combustion can be divided into two categories: slow combustion and detonation. The vast majority of fires in daily life belong to slow ignition, while detonation is mainly seen in explosives and the like.

To cause combustion, three elements must be present: combustibles, combustion aids, and a temperature not lower than the ignition point. These three elements are also known as the "iron triangle" of combustion.

According to our common sense, combustion generally produces flames, but not all combustion produces flames. Some combustion only emits white smoke, which is also known as smoldering.

It can be seen that flames and smoldering correspond, one emitting light and the other not emitting light.

Is the flame a substance or a phenomenon? If it is a substance, it will definitely be affected by gravity. If it is just a phenomenon, it cannot be said whether it is affected by gravity or not.

Flame is actually a phenomenon of luminescence. When combustible materials reach a certain temperature, they enter an incandescent state, which generates visible light.

The essence of incandescence is that particles in combustible materials release photons due to the absorption of a large amount of energy, which are the fundamental units of light we see.

Since flames are a phenomenon, it means that discussing whether flames are subjected to gravity alone is meaningless. The essence of the problem we want to explore is not here.

The figure shows: buoyancy

A force opposite to gravity - buoyancy

In 245 BC, Archimedes discovered the principle of buoyancy when he took a bath.

He believes that an object immersed in water will experience a vertical upward force, which is equal to the weight of the water released by the object.

The generalization of this discovery is that in a fluid (gas, liquid), the sum of the fluid pressures (vector sum) on each surface of an object is called buoyancy.

Something that falls into the water will float up, while others will sink to the bottom. This is because some objects in the water have greater buoyancy than gravity, while others have less buoyancy than gravity.

A concept closely related to buoyancy is density. Density is a physical quantity used to describe the density of an object, which refers to the mass contained in a unit of volume. This can be seen from its basic unit kg/m ^ 3.

From the perspective of density, we can more concisely describe the rise and fall of objects: still using water as an example.

For an object in water, it sinks when its density is greater than that of water, rises when its density is less than that of water, and suspends in water when their density is equal

The same principle holds true in the air.

When various parts of the air are heated unevenly, the density of gases with higher temperatures will decrease and increase, while those with lower temperatures and relatively higher densities will decrease and supplement the vacancies left by the rising air.

This is the essence of convective phenomena in the air.

How did flames actually form

According to the previous description, compared to the issue of whether flames are subjected to gravity, we should explore more about how flames are formed or why they exhibit the shape we see.

Taking a burning candle as an example, why does its flame show a straight upward trend?

In fact, the combustible substance in candles is paraffin, which has a melting point of around 50 and a boiling point of approximately 300-500 . The process of lighting a candle is actually the process of transforming paraffin from solid to liquid and then into paraffin gas.

Under the influence of external temperature, paraffin gas enters an incandescent state, and its internal particles absorb a large amount of energy and begin to release photons, thus we can see the flame of the candle.

Because photons are released by particles in the paraffin gas, the shape of the flame is also the distribution position of the paraffin gas. The flame is slender and in an ascending form, and we can say that paraffin gas is in an ascending state.

The figure is: Schematic diagram of flame convection

Why does paraffin gas rise?

We have already mentioned the phenomenon of convection, and the rise of paraffin gas belongs to the phenomenon of convection.

The density of the heated paraffin gas becomes lower due to thermal expansion, thus rising (that is, the buoyancy is greater than gravity), while the density of the surrounding cold density of air is relatively large, so it settles below the paraffin gas.

We can also say that it is cold air that lifts the paraffin gas, causing the fire to burn upwards, resulting in an upward trend of the flame.

The picture is: comparison of normal gravity (left) and microgravity (right) flames

It can be seen that the root cause of flame formation is still inseparable from gravity. A foreign experiment found that the flame of a candle is spherical in a gravity free environment.

This is because without gravity, there would be no buoyancy, and without buoyancy, there would be no convection. The paraffin gas would not be lifted or compressed, and it would drift in any direction, resulting in a spherical flame.

The picture shows a flame ignited in space

last

There is such a vast universe in a small flame, and this is precisely the charm of science. There are many common phenomena in life, and the underlying principles are worth exploring.

By the way, it seems that there are no objects on this planet that can escape the constraints of gravity!

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