Physics

Article Definition of heat Mechanical equivalent of heat Equation of heat

1. Definition of heat

If objects that have temperature differences touch each other, there will be heat transfer from high-temperature objects to low-temperature objects. Heat transfer stops after touching objects reach the same temperature. For example, if we mix hot water with cold water, usually heat moves from hot water to cold water. When we put hot iron into cold water, heat moves from iron to water. Heat will stop flowing after iron and water reach the same temperature. When a nurse attaches a thermometer to your body, heat moves from

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Article about Anomalous behavior of water below 4°C

Each object expands (the volume of objects increases) when the temperature increases, and objects shrink (the volume of objects decreases) when the temperature decreases. Water also expands when the temperature increases and shrinks when the temperature decreases, but not at 0 ^oC – 4 ^oC. Between 0 °C and 4 °C, the volume of water decreases (water shrinks) as temperature increases. If we heat the water at 0 ^oC, the water gets hotter, the water volume decreases. The shrinkage process stops when the water reaches 4 ^oC. Above 4 ^oC, the volume of water increases as temperature increases. Instead, water expands (the volume of water increases) when the temperature decreases from 4 ^oC to 0 ^oC.

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Most solid objects experience a linear expansion when the temperature changes. The linear expansion is the length of the object increases or the length of the object decreases. Usually, the length of the object increases when the temperature increases, whereas the length of the object decreases when the temperature drops. You might think that linear expansion can only occur on objects such as thin wires. For example, look at a car that is parked on the side of the road, so it is exposed to the sun. When the car overheats, the iron plate can get thicker, or the side length can increase. Roofs of houses made of zinc can also experience expansion. In this case, when zinc is overheated, the edges of zinc increase in width and zinc can even get thicker. The same thing happened to the railroad tracks and iron or steel on the bridge.

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Article about Conversion of temperature scale

The Celsius scale and the Fahrenheit scale are different temperature scales. If the temperature of an object is measured and expressed on a Celsius scale, then we want to state the temperature of the object on the Fahrenheit scale then we change it from the Celsius scale to the Fahrenheit scale. In this section, we learn to change or convert a temperature scale.

At a pressure of 1 atm, the temperature of the freezing point for the Celsius thermometer = 0 ^oC, while the Fahrenheit thermometer = 32 ^oF. Conversely, at a pressure of 1 atm, the temperature of the boiling point for a Celsius scale thermometer = 100 ^oC, while a thermometer with a Fahrenheit scale = 212 ^oF.

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Article about Thermometers and temperature scales

1. Thermometers

The tool designed to measure temperature is a thermometer. There are many types of thermometers, but the working principle is the same. Usually, we use thermometric objects, the nature of matter that changes with temperature. If the temperature of the object changes, the shape, and size of the object also changes. Most thermometers use objects that can expand or shrink when the temperature changes. Thermometers that are often used consist of glass tubes, where there is alcohol or mercury in the center of the tube. When the temperature increases, alcohol or mercury in the container expands so that the length of the alcohol or mercury column increases. Conversely, when the temperature decreases, the length of the alcohol or mercury column decreases. On the outside of the glass tube, there are numbers which are the scale of the thermometer. The number shown by the upper end of the alcohol or mercury column states the value of the temperature of the object being measured.

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Article about The Zeroth Law of Thermodynamics

So far, we have only observed the thermal equilibrium experienced by two objects in contact.

To understand the concept of thermal equilibrium in more depth, let’s review three objects (say objects A, object B, and objects C). For example, object B and object C do not touch each other, but object A in contact with object B and object A in contact with object C. Observe the image below. Because in contact with each apart from object A and object B are in thermal equilibrium, so also object A and object C are in thermal equilibrium. Are objects B and C that do not touch each other also in thermal equilibrium? If we only use logic, we can say that object B and object C are also in thermal equilibrium, even though they are not in contact. Object A and object B are in thermal equilibrium, meaning the temperature of the object A = the temperature of object B.

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Article about Definition of temperature and thermal equilibrium

Definition of temperature

Ever touched ice? What do you feel when your hands touch ice? What if what you touch is fire? When touching ice, your hands feel cold, when you touch the fire, your hands feel hot. Hot, warm, cool, cold states what?

The concept of temperature starts from the heat and cold experienced by our sense of touch. Based on what is felt by the sense of touch, we say an object is hotter than another object or an object is cooler than another. Hot objects have higher temperatures, while cold objects have lower temperatures. The cooler an object, the lower the temperature. Conversely, the hotter an object, the higher the temperature. The size of the heat or cold of an object is called temperature. In the subject of gas kinetic theory, you will understand more deeply the definition of temperature; what happens to the molecules from an object so that it can feel hot, warm, cool or cold.

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Article about Phases of matter (based on microscopic properties)

In everyday life, we often encounter three different phases of matter. There are solid substances (e.g., stones, iron, etc.), liquids (water, gasoline, etc.) and gas substances (air, etc.). The three-phase of these substances can be distinguished based on their ability to maintain their shape and size.

Solids usually maintain a fixed shape and volume. The liquid does not keep an attached form, but adjusts its way to the container that is occupied. For example, if we put water in a glass, the shape changes like a glass. If water is put into the bathtub, the shape changes like a bathtub. The volume of liquid is typically always fixed. A glass of water if it is placed in a bath, the amount of water remains in a glass. The shape of the water can change, but the size never varies. Keep in mind that the number of solids and liquids can change if given a considerable force.

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Article about Atomic theory and kinetic theory

Atomic theory

For thousands of years, the ancient Greeks believed that every pure substance (such as gold, iron, etc.) consisted of atoms. According to them, if a pure substance is cut into small pieces, then the tiny parts are cut again, then cut back… and so on, then there will be the smallest pieces that cannot be cut again. The smallest pieces that cannot be cut again are called atoms. Atom means “cannot be divided” (Greek language)

At that time, the atom is considered to be no longer divided. But later some scientists discovered electrons and atomic nuclei (protons and neutrons) so that the assumption that atoms could not be subdivided was wrong. So, atoms consist of electrons (negatively charged) and atomic nuclei. Electrons circle the nucleus. Inside the nucleus, there are protons (positively charged) and neutrons (neutral or not charged).

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Article about Changes of phase Critical temperature Triple point

In the discussion of the ideal gas law, it has been explained that the ideal gas law describes the behavior of real gas accurately only when the pressure and density of real gas are not too large. If the pressure and real gas density are large enough, the ideal gas law provides inaccurate results, likewise, when the temperature of real gas approaches the boiling point. This is related to the interactions that occur between real gas molecules. Gas pressure is inversely proportional to gas volume. When the gas pressure is large enough, the gas volume becomes smaller. Because the gas volume is low, the distance between the gas molecules becomes closer. When the distance between molecules becomes closer, the molecules attract each other. It’s like when you put a piece of iron on a magnet. If the distance between the magnet and iron is far enough, the magnet cannot pull iron. But if the distance between magnet and iron is close, iron is drawn closer.

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