Name: thermal equilibrium and the zeroth law
Uploaded: 2025-05-22T09:05:48.000Z
Duration: 1 min 14 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Chemistry

Energy

HS-PS3-4

Zeroth Law of Thermodynamics

חוק האפס של התרמודינמיקה קובע שאם שני גופים נמצאים בשיווי משקל תרמי עם גוף שלישי, הם גם נמצאים בשיווי משקל תרמי זה עם זה.
כדי להבין זאת בניסוי, חשבו על שלוש כוסות מלאות במים בשלוש טמפרטורות שונות.
לאחר חיבור A עם B וכוס B עם C, העברת חום תתבצע.
לאחר פרק זמן, המים בכד א' מגיעים לשיווי משקל תרמי עם המים בכד ב', והמים בכד ב' מגיעים לשיווי משקל עם המים בכד ג'.
ברישום הטמפרטורה של הכוסות, טמפרטורה אחידה נצפית בכל שלושת הכוסות, התואמת את חוק האפס של התרמודינמיקה.
היישום המשמעותי ביותר של חוק האפס של התרמודינמיקה הוא סוגים שונים של מדי חום.
כאשר מדחום משמש למדידת הטמפרטורה של גוף, הוא משיג שיווי משקל תרמי על ידי שינוי הטמפרטורה שלו.
לפיכך, הטמפרטורה הנמדדת של הגוף היא למעשה הטמפרטורה של המדחום.

<ol>
	<li>OpenStax. (2019). פיזיקה אוניברסיטאית כרך 2. [גרסת אינטרנט]. מקור: <a href="https://openstax.org/books/university-physics-volume-2/pages/1-1-temperature-and-thermal-equilibrium">https://openstax.org/books/university-physics-volume-2/pages/1-1-temperature-and-thermal-equilibrium</a></li>
</ol>

חוק האפס של התרמודינמיקה

<div style="direction:rtl">באופן ניסוי, אם אובייקט A נמצא בשיווי משקל עם אובייקט B, והאובייקט B נמצא בשיווי משקל עם אובייקט C, אז אובייקט A נמצא בשיווי משקל עם אובייקט C. הצהרה זו של מעבריות נקראת "חוק האפס של התרמודינמיקה." לדוגמה, בלוק מתכת קר ובלוק מתכת חם מונחים שניהם על לוח מתכת בטמפרטורת החדר. בסופו של דבר, הבלוק הקר והצלחת יהיו בשיווי משקל תרמי. בנוסף, הבלוק החם והצלחת יהיו בשיווי משקל תרמי. לפי חוק האפס, אנו יכולים להסיק שהגוש הקר והגוש החם נמצאים גם הם בשיווי משקל תרמי. הפיזיקאי הבריטי ראלף פאולר הציע את המספר "אפס" בשנות ה-30. באותו זמן, החוקים הראשון, השני והשלישי של התרמודינמיקה כבר נקראו וממוספרים. החוק האפס נאמר רק לעתים רחוקות, אבל היה צורך לדון בו לפני האחרים, אז פאולר נתן לו מספר קטן יותר. עכשיו שקול את המקרה שבו A הוא מדחום. חוק האפס אומר לנו שאם A קורא טמפרטורה מסוימת כשהיא בשיווי משקל עם B, ואז היא מונחת במגע עם C, היא לא יחליף אנרגיה עם C; לכן קריאת הטמפרטורה שלו תישאר זהה. במילים אחרות, אם שני עצמים נמצאים בשיווי משקל תרמי, יש להם אותה טמפרטורה.</div>

באופן ניסיוני, אם אובייקט A נמצא בשיווי משקל עם אובייקט B, ואובייקט B נמצא בשיווי משקל עם אובייקט C, אז אובייקט A נמצא בשיווי משקל עם אובייקט C.

Education

JoVE Core

Physics

פיזיקה

Unit 1

יחידה 1

Temperature and Heat

טמפרטורה וחום

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

thermal equilibrium and the zeroth law

The zeroth law of thermodynamics explains thermal equilibrium between objects. If object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is also in equilibrium with object C. This transitive relationship is the key idea behind the law.

A simple example uses metal blocks and a metal plate at room temperature. A cold metal block and a hot metal block are both placed on the plate. Over time, the cold block and the plate reach thermal equilibrium, and the hot block and the plate do too. By the zeroth law, the cold block and the hot block are then also in thermal equilibrium.

The law also helps explain how thermometers work. If a thermometer is in equilibrium with one object and then placed in contact with another object, it will not exchange energy with that object if their temperatures match. Its reading stays the same. In other words, two objects in thermal equilibrium have the same temperature.

The name zeroth law was suggested by British physicist Ralph Fowler in the 1930s. By then, the first, second, and third laws of thermodynamics had already been named. The zeroth law was less often stated, but it had to be discussed before the others, so Fowler gave it the smaller number.

Thermal Equilibrium and the Zeroth Law

temperature and thermal equilibrium

Heat, Temperature, and Everyday Energy

Heat and temperature are key ideas in thermodynamics and in everyday life. People often connect temperature with hot and cold, but science gives it a more precise meaning. Temperature is the quantity measured with a thermometer. It is also linked to the average translational kinetic energy of particles. Heat is different from temperature. Heat is energy that moves from one place or material to another because there is a difference in temperature. That difference in temperature keeps heat...

zeroth law of thermodynamics

The zeroth law of thermodynamics explains thermal equilibrium between objects. If object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is also in equilibrium with object C. This transitive relationship is the key idea behind the law. A simple example uses metal blocks and a metal plate at room temperature. A cold metal block and a hot metal block are both placed on the plate. Over time, the cold block and the plate reach thermal equilibrium, and...

thermometers and temperature scales

How Thermometers Measure Heat

Thermometers measure temperature by using physical properties that change in a predictable way. One common example is volume. For most substances, volume increases as temperature rises. That idea is used in alcohol thermometers and in the original mercury thermometers. Other thermometer designs use different temperature-sensitive properties. Some measure electrical resistance, color, or the emission of infrared radiation. The alcohol thermometer is a common example. It contains red-dyed...

gas thermometers and the kelvin scale

Kelvin Temperature and Gas Thermometer Standards

Kelvin temperature is the absolute scale used in science, and it starts at absolute zero. That zero point matches the lowest possible temperature, where molecular motion reaches zero or the minimum allowed by quantum mechanics. Scientists use this scale because some physical quantities, such as the volume of an ideal gas, depend directly on absolute temperature. The Kelvin scale is part of the SI system of units, so its definition is more precise than simply using water’s freezing and boiling...

thermal expansion

Thermal Expansion in Air, Water, and Solids

Thermal expansion is the change in size or volume of a material as its temperature changes. A common example is the alcohol inside a thermometer. As the temperature rises, the alcohol expands and shows the change. Heated air also expands. It becomes less dense than the cooler air around it, so the surrounding air pushes it upward. This is why steam and smoke rise and why hot air balloons float. The same effect happens in liquids and gases, and it helps move heat upward in homes, oceans, and...

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How Temperature Changes Create Stress

Thermal stress is the stress that builds up when an object changes temperature but cannot expand or contract freely. If the object would expand without restraint, the stress is compressive. If it would contract, the stress is tensile. This stress from heating or cooling can become large enough to cause damage. Engineers often reduce it by designing parts so they can move as temperature changes. Highway blocks, for example, are separated by gaps so thermal stress does not build up. When gaps...

thermal expansion and thermal stress: problem solving

thermal-expansion-and-thermal-stress-problem-solving

Golden Gate Bridge Thermal Expansion

Thermal expansion and thermal stress are shown through the Golden Gate Bridge. The bridge faces temperatures from -15 °C to 40 °C. At its coldest, the main span is 1275 m long. Assuming the bridge is made entirely of steel, the example asks for the change in its length across this temperature range. To solve the problem, the known values must be identified first. The initial length is 1275 m. The coefficient of linear expansion for steel is 12 x 10 -6 /°C, and the change in temperature is 55...

heat flow and specific heat

Heat Units and Specific Heat

Heat is energy transferred because of a temperature difference, and it can change an object’s temperature. Since heat is energy, its SI unit is the joule (J). Heat transfer is the movement of energy from one place or material to another, and it plays a role in home heating, cooking, and many industrial processes. Two common units for heat are the calorie and the kilocalorie. A calorie (cal) is the energy needed to change the temperature of 1 g of water by 1 °C, specifically between 14.5 °C and...

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Heat and Phase Change Energy

Heat and phase change energy explain why substances melt, freeze, boil, and condense. A solid turns into a liquid during melting, also called fusion. The reverse process is freezing. A liquid turns into a gas during evaporation. The reverse process is condensation. Each substance changes phase at specific temperatures. The melting point is the temperature where a substance melts or freezes. The boiling point is the temperature where a substance boils or condenses. These temperatures depend on...

calorimetry

Heat Exchange in an Insulated System

Calorimetry studies heat exchange in an insulated system. A calorimeter is a container that prevents heat transfer in or out. Scientists use calorimetry to measure heat and specific heat capacity. A calorimetry problem is any situation where the objects are thermally isolated from their surroundings. The key idea comes from conservation of energy. During heat transfer, the heat gained by the colder object must equal the heat lost by the hotter object. A simple example is water poured into a...

mechanisms of heat transfer i

Three Ways Heat Moves Between Objects

Heat transfer happens when there is a temperature difference. It can move fast, like through a cooking pan, or slowly, like through the walls of a picnic ice box. Heat transfer appears in many everyday situations, so it is hard to find a place where it does not occur. There are only three ways heat is transferred: conduction, convection, and radiation. A fireplace shows all three at once. Radiation carries most of the heat into the room. Conduction also moves heat into the room, but much more...

mechanisms of heat transfer ii

Convection and Radiation in Heat Transfer

Convection and radiation are two major ways heat moves. In convection, thermal energy is carried by the large-scale flow of matter. Warm air and water rise because they are less dense, so ocean currents and large-scale atmospheric circulation move heat from the tropics toward the poles and move cold air from the poles toward the tropics. Earth’s rotation changes these moving air currents. It interacts with the flow and helps produce the eastward movement of air in the temperate zones.

conduction, convection and radiation: problem solving

conduction-convection-and-radiation-problem-solving

Heat Transfer Calculations with Conduction, Convection

Heat transfer calculations with conduction and convection use the temperature difference to find the rate of heat flow. Radiation can also be part of the process. The main idea is that heat moves only because one area is hotter than another, and a larger temperature difference leads to faster transfer. To solve a heat transfer problem, first identify the type of transfer involved. It may be conduction, convection, radiation, or a combination of all three. Next, write down the unknown...

radiation: applications

Earth’s Energy Balance and Greenhouse Effect

Earth’s energy balance and the greenhouse effect help explain its average temperature. Earth is in radiative contact with both the Sun and dark space. It receives almost all of its energy from solar radiation, and it reflects some of that energy back into outer space. Dark space is very cold, about 3 K, so Earth also radiates energy into it. Heat can move quickly from soil and grasses, and frost can form on clear summer evenings, even in warm latitudes. In a first approximation, Earth’s...

absorption of radiation

Radiation Heat Transfer and Thermographs

Radiation heat transfer depends on temperature, surface area, and emissivity. The Stefan-Boltzmann law describes the rate of heat transfer by emitted radiation. In this law, σ is the Stefan-Boltzmann constant, A is the object’s surface area, and T is its temperature in kelvins. The fourth-power dependence on absolute temperature makes radiation highly sensitive to small temperature changes. Even a slight rise in temperature can change the emitted heat a lot. That sensitivity is why radiation...

key terms and concepts

Learn how the zeroth law of thermodynamics shows that objects in thermal equilibrium have the same temperature and why this matters for thermometers.

Thermal Equilibrium and the Zeroth Law | JoVE K12

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HS-PS3-6

Thermal Equilibrium and the Zeroth Law

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