 # Does a fire weigh? Can a pound of fire boil 10 pounds of water

2020-01-09 | Zhong Ming talks about science original |

In fact, mass is the property of matter, as is energy. Therefore, there is mass in energy, and mass has energy. Therefore, a pound of "electricity" exists, and the same pound of "fire" also exists, but weThey are usually described in terms of energy units. So it seems strange to use weight to describe it. So what is going on? Can a pound of fire boil 10 litres of water?

mass energy equivalent

This matter actually starts with mass-energy equivalence. You may be new to this name. But there is one of the most famous equations in the history of physics in mass-energy equivalence theory, and that is the mass-energy equation E = mc ^2. This was proposed by Einstein in 1905. what exactly does mass-energy equivalence say?

To understand this problem, we must first look at the description in the famous paper of 1905, which was published in the Yearbook of Physics on September 27 of that year. He said so, if there is an object that emits energy E in the form of radiation, its mass will decrease by m / c ^ 2.

Actually, he still has a large paragraph later, which will not be quoted here. So how do we understand this sentence?

Let's take one of the most common atomic bomb explosions. The principle of an atomic bomb is a nuclear fission reaction. Nuclear fission actually refers to a heavy nuclear fission becoming a smaller atomic nucleus. Before and after this reaction, the mass was lost. Specifically, the mass of U235 + neutron is greater than 144Ba + 90Kr + 2 neutrons. Where did the missing mass go?

If we consider this part of mass as m, then it is the energy equivalent to mc ^ 2 released. Therefore, this part of the energy produced by the atomic bomb actually has mass, and the mass is m. Many peopleYou will understand the transformation relationship. In fact, this is not true. This is because mass is an attribute of matter, not something, and so is energy. But because there are so many misunderstandings, physicists at universities todayHere are deliberately rumors, emphasizing equivalence rather than transformation

Einstein unified mass and energy through a mass-energy equation, letting us know that energy and matter are two sides of an object. How much energy does a pound of fire have?

Then we continue to return to the question we just talked about. After understanding the mass-energy equivalence, we will know that fire also has weight. But we have to talk about what is "fire" first?

Objectively speaking, this problem is actually very complicated, so complicated that it may not be clear with one article. Here we will briefly explain the definition of fire.

Fire refers to the strong oxidation reaction of a substance during the combustion process and its ability is released in the form of light and heat, and a large number of products are generated. The visible part of the fire is called the flame, and it can show different status quo with the vibration of the particles, and appear in the form of plasma when the temperature is high enough. Additionally, the plasma state is different from the commonThree states: gaseous, solid, and liquid. In this state, the electrons are no longer bound by the nucleus, and they begin to mess. To sum up, fire actually generates heat, or energy transfer due to thermal contact. Then we can use the mass energy equation to convert the energy E corresponding to the fire. E = mc ^ 2, where m = 1kg, c = 3 * 10 ^ 8m / c, and the calculation will get E =9 * 10 ^ 16J.

Can a pound of fire boil 10 litres of water?

Then we assume that 10L of water is boiled down at a standard atmospheric pressure at room temperature of 25 degrees. Here we need to use the specific heat capacity formula of water. With a simple shift term, we will get the required energy Q = cm △ t, where c can be approximately 4.2 * 10 ^ 3J / kg · K, m = 10kg, △ t = 100-25 =75. Here, a sentence of 10 liters of water can be regarded as approximately 10 kg. This is because the density of water is 1.0 * 10 ^ 3 kg / m3. Finally, we can get the energy required to boil 10 liters of water Q = 3.15 * 10^ 6J.

The energy of a pound of fire is 9 * 10 ^ 16J, which is a difference of 10 orders of magnitude. That is, even if the conversion rate is as low as one tenth of a billion, 10 liters of water can be boiled.

And if we use a large pot to burn 10 liters of water with fire, the conversion rate is actually many orders of magnitude greater than one tenth of a billion. Therefore, it is easy to boil 10 litres of water with a pound of fire, and it should be said that it does not use a pound at all.

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