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

Wenn eine Tasse heißer Kaffee in einem Raum aufgestellt wird, sinkt ihre Temperatur, da sie ein thermisches Gleichgewicht mit der Atmosphäre erreicht.
Die Energie, die aufgrund des Temperaturgradienten vom Kaffee übertragen wird, wird als Wärme bezeichnet, und die Energieübertragung, die dabei stattfindet, wird als Wärmefluss bezeichnet.
Die SI-Einheit der Wärme ist das Joule. Eine weitere Standardeinheit für Wärme ist die Kalorie, wobei eine Kalorie 4,186 Joule entspricht.
Ferner ist die Wärmemenge, die erforderlich ist, um die Temperatur der Masse m eines bestimmten Materials von T1 auf T2 zu erhöhen, proportional zur Masse und zur Temperaturänderung. Die Proportionalitätskonstante c wird als spezifische Wärme bezeichnet.
Spezifische Wärme ist also die Wärmemenge, die erforderlich ist, um die Temperatur einer Masseneinheit eines Stoffes um ein Grad Celsius zu erhöhen.
Wenn die molare Masse, d. h. die Masse pro Mol eines Stoffes, in der Formel für die spezifische Wärme verwendet wird, wird sie als molare Wärmekapazität bezeichnet und mit dem großen C bezeichnet.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/details/books/university-physics-volume-2">https://openstax.org/details/books/university-physics-volume-2</a>; S. 19–20.</li>
</ol>

wärmeübertragung und spezifische wärme

Wärme ist eine Form des Energieübertrags, die durch einen Temperaturunterschied verursacht wird und die Temperatur eines Objekts verändern kann. Da Wärme eine Form von Energie ist, ist ihre SI-Einheit das Joule (J). Eine weitere häufig verwendete Energieeinheit für Wärme ist die Kalorie (cal), die definiert ist als die Energie, die benötigt wird, um die Temperatur von 1 g Wasser um 1 °C zu ändern, insbesondere zwischen 14,5 °C und 15,5 °C, da die benötigte Energie eine leichte Temperaturabhängigkeit aufweist. Eine weitere gebräuchliche Einheit ist die Kilokalorie (kcal), die die Energie angibt, die benötigt wird, um die Temperatur von 1 kg Wasser um 1 °C zu ändern. Da die Masse in der Regel in Kilogramm angegeben wird, ist die Kilokalorie praktischer. Verwirrenderweise sind Nahrungskalorien tatsächlich Kilokalorien, eine Tatsache, die nicht leicht aus der Verpackungsetikettierung zu entnehmen ist.

Wärmeübertragung ist die Bewegung von Energie von einem Ort oder Material zum anderen aufgrund eines Temperaturunterschieds. Die Wärmeübertragung ist fundamental für alltägliche Aktivitäten wie Heizung und Kochen zu Hause sowie für viele industrielle Prozesse.

Die spezifische Wärme hängt vom Material und seiner Phase ab. Zum Beispiel ist die spezifische Wärme von Wasser 5-mal größer als die von Glas und 10-mal größer als die von Eisen, was bedeutet, dass es 5-mal mehr Wärme benötigt, um die Temperatur von Wasser im Vergleich zu Glas und 10-mal mehr im Vergleich zu Eisen zu erhöhen. Tatsächlich hat Wasser eine der größten spezifischen Wärmen aller Materialien, was für das Leben auf der Erde wichtig ist. Der Wert der spezifischen Wärme muss in der Regel gemessen werden, da es keine einfache Möglichkeit gibt, ihn genau zu berechnen.

Wärmeübertragung und spezifische Wärme

Wärme ist eine Art der Energieübertragung, die durch einen Temperaturunterschied verursacht wird und die Temperatur eines Objekts verändern kann. Da Hitze eine Form von ...

Education

Lehre

JoVE Core

Physik

Unit 1

Einheit 1

Temperature and Heat

Temperatur und Wärme

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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

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Kelvin Temperature and Gas Thermometer Standards

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

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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

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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.

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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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Force and Potential Energy in One Dimension

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Force and Potential Energy in Three Dimensions

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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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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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