Name: heat units and specific heat
Uploaded: 2023-04-30T12:29:39.000Z
Duration: 1 min 12 s
Channel: JoVE

K12 Standards

Tennessee Academic Standards

High School

Physics

Energy

PHYS.PS3.2

Heat Flow and Specific Heat

Quando una tazzina di caffè caldo viene posta in una stanza, la sua temperatura si riduce man mano che raggiunge l'equilibrio termico con l'atmosfera.
L'energia che viene trasferita dal caffè a causa del gradiente di temperatura è chiamata calore e il trasferimento di energia che avviene nel processo è chiamato flusso di calore.
L'unità di misura del calore SI è il joule. Un'altra unità standard di calore è la caloria, dove una caloria è uguale a 4,186 joule.
Inoltre, la quantità di calore necessaria per aumentare la temperatura di massa m di un determinato materiale da T1 a T2 è proporzionale alla massa e alla variazione di temperatura. La costante di proporzionalità c è chiamata calore specifico.
Quindi il calore specifico è la quantità di calore necessaria per aumentare la temperatura di un'unità di massa di una sostanza di un grado Celsius.
Se la massa molare, che è la massa per mole di una sostanza, viene utilizzata nella formula per il calore specifico, si chiama capacità termica molare ed è indicata con la C maiuscola.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Estratto da <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a>; pagine 19-20.</li>
</ol>

flusso di calore e calore specifico

Il calore è un tipo di trasferimento di energia che è causato da una differenza di temperatura, e può cambiare la temperatura di un oggetto. Visto che il calore è una forma di energia, la sua unità SI i il joule (J). Un'altra unità comune di energia che viene usata spesso per il calore è la caloria (cal), che è definita come l'energia necessaria per cambiare la temperatura di 1g d'acqua di 1°C, in particolare tra 14.5°C e 15.5°C, dato che l'energia necessaria mostra una leggera dipendenza dalla temperatura. Un'altra unità comunemente usata è la kilocaloria (kcal), che è l'energia necessaria a cambiare la temperatura di 1kg d'acqua di 1°C. Dato che la massa è più spesso specificata in chilogrammi, la kilocaloria è più conveniente. Confusamente, le calorie del cibo in realtà sono kilocalorie, un fattore non facilmente determinato dall'etichetta del pacchetto.

Il trasferimento di calore è il movimento di energia da un posto o materiale ad un altro come risultato di una differenza di temperatura. Il trasferimento di calore è fondamentale nelle attività quotidiane come scaldare una casa e cucinare, nonché per molti processi industriali.

Il calore specifico dipende dal materiale e dalla sua fase. Per esempio, il calore specifico dell'acqua è 5 volte quello del vetro e 10 volte quello del ferro, il che significa che serve 5 volte più calore per aumentare la temperatura dell'acqua rispetto al vetro e 10 volte di più rispetto al ferro. Infatti, l'acqua ha uno dei più grandi calori specifici rispetto a qualsiasi altro materiale, il che è importante per sostenere la vita sulla Terra. Il valore del calore specifico deve generalmente essere misurato perché non esiste un modo semplice per calcolarlo con precisione.

Flusso di calore e calore specifico

Il calore è un tipo di trasferimento di energia causato da una differenza di temperatura e può modificare la temperatura di un oggetto. Poiché il calore è una forma di ...

Education

Didattica

JoVE Core

Fisica

Unit 1

Unità 1

Temperature and Heat

Temperatura e Calore

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 15.5 °C because the value changes slightly with temperature. A kilocalorie (kcal) is the energy needed to change the temperature of 1 kg of water by 1 °C. Kilocalories are often more convenient because mass is usually given in kilograms. Food calories are actually kilocalories, even though labels do not always make that clear.

Specific heat depends on the material and its phase. It tells how much heat is needed to raise a substance’s temperature. Water has a specific heat about 5 times that of glass and 10 times that of iron. That means water needs much more heat to warm up by the same amount, and it has one of the largest specific heats of any material. This high value is important for life on Earth.

Specific heat usually must be measured. There is no simple way to calculate it exactly. Understanding heat flow and specific heat helps explain why different materials warm up and cool down at different rates.

Heat Units and Specific Heat

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

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...

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...

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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...

thermal stress

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 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...

phase changes

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 heat is measured in joules, calories, and kilocalories, and why specific heat makes water warm up more slowly than glass or iron.

Heat Units and Specific Heat | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

PHYS.PS3.5

Chemistry

CHEM1.PS3.1

Virginia  Standards of Learning

HIgh School

Physical Science

PS.5

PS.5.b

Minnesota Academic Standards in Science

9-12

1.2.1 9C.4.2.1.2

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New Jersey Student Learning Standards for Science

HS-PS3-4

Arizona Science Standards

HS+Phy.P4

HS+Phy.P4U2.7

HS.P4

HS.P4U1.8

HS+Phy.P4U1.6

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.D

Alabama Course of Study Science

9-12.PS.1.1.c

Earth and Space Science

Earth's Systems

9-12.ESS.2.7

9-12.ESS.2.7.b

Georgia Standards of Excellence

SPS7.

Specific Heat

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Identify and calculate different types of energy and their transformations (thermal, kinetic, potential, including magnetic and electrical potential energies) from one form to another in a system. Identify and calculate different types of energy and their transformations (thermal, kinetic, potential, including magnetic and electrical potential energies) from one form to another in a system. EXPLANATION:  In 6.PS3 students were introduced to the various types of energy and mechanisms for their transformations. Students should now be able to quantify the total energy of a system as well as quantify each different type of energy in a system. Energy is an abstract concept that does not have a physical form. It is a substance-like quantity that is recognized to be conserved as a system changes. Calculations present an opportunity to observe that potential energies are due to the positions of objects within a field, while kinetic energy is based on an object’s mass and motion. Students can evaluate the total energy of a system by imagining that there are different types of energy storage accounts, just as money can be stored in different accounts. Energy can transferred into or out of any of these accounts. Three different processes can account for all energy changes: working, heating, and radiating. In energy storage due to field effects, such as gravitational or electrostatic fields, the field itself stores the potential energy and not the object in the field.

PHYS.PS3.1

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Free-falling Bodies: Example

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Force and Potential Energy in One Dimension

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Force and Potential Energy in Three Dimensions

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Energy Diagrams - II

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Use the principle of energy conservation and mathematical representations to quantify the change in energy of one component of a system when the energy that flows in and out of the system and the change in energy of the other components is known.         Use the principle of energy conservation and mathematical representations to quantify the change in energy of one component of a system when the energy that flows in and out of the system and the change in energy of the other components is known.         EXPLANATION:  In PHYS.PS3.1 students quantify the various types of energy and consider methods for energy transfer. If a student is able to evaluate the total energy of a system, such evaluations before and after a change to a system provide a mechanism to show that energy of a system has been conserved. For example, students might use pie charts to show the distribution of the total energy. For an object about to freefall, the pie chart might be 100% gravitational potential energy. Mid-descent, the energy might be half gravitational potential energy and half kinetic energy. After colliding with the ground, the total energy may have decreased, which can be represented as heat energy lost from the pie chart.

PHYS.PS3.3

Linear Momentum

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Impulse

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Impulse-Momentum Theorem

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Collisions in Multiple Dimensions: Introduction

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Collisions in Multiple Dimensions: Problem Solving

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PHYS.PS3.4

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Define power and solve problems involving the rate of energy production or consumption (P=∆E/∆t). Explain and predict changes in power consumption based on changes in energy demand or elapsed time. Investigate power consumption and power production systems in common use.  Define power and solve problems involving the rate of energy production or consumption (P=∆E/∆t). Explain and predict changes in power consumption based on changes in energy demand or elapsed time. Investigate power consumption and power production systems in common use. EXPLANATION:  This standard pairs well with PHYS.PS3.6. Students should understand that a given task will require a certain minimum amount of energy. In accordance with the work-energy theorem, this would be described as work done on the system. Power incorporates a rate element into this discussion. An object can be lifted to an identical height by two different mechanisms. The total energy input into the system (the object and Earth’s gravitational field) will be the same in either case. However, if one mechanism for lifting the object does this in a smaller amount of time, it is said to be more powerful. Students may compare two different devices that accomplish the same task, but have different power ratings and explain the impact of the different power ratings on how the devices are used. For example, two microwaves might both pop a bag of popcorn, but a more powerful microwave might do it faster or be more likely to burn the popcorn at recommended time settings.

PHYS.PS3.6

Heat Units and Specific Heat

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