# Temperature - Key terms

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### ABSOLUTE ZERO:

The temperature, defined as 0K on the Kelvin scale, at which the motion of molecules in a solid virtually ceases.

### CELSIUS SCALE:

A scale of temperature, sometimes known as the centigradescale, created in 1742 by Swedish astronomer Anders Celsius (1701-1744). The Celsius scale establishes the freezing and boiling points of water at 0° and 100°, respectively. To convert a temperature from the Celsius to the Fahrenheit scale, multiply by 9/5 and add 32. The Celsius scale is part of the metric system used by mostnon-English speaking countries today. Though the worldwide scientific community uses the metric or SI system for most measurements, scientists prefer the related Kelvin scale.

### FAHRENHEIT SCALE:

The oldest of the temperature scales still used in Westernnations today, created in 1714 by German physicist Daniel Fahrenheit (1686-1736). The Fahrenheit scale establishes the freezing and boiling points of water at 32° and 212° respectively. To convert a temperature from the Fahrenheit to the Celsius scale, subtract 32 and multiply by 5/9. Most English-speaking countries use the Fahrenheitscale.

### HEAT:

Internal thermal energy that flows from one body of matter to another.

### KELVIN SCALE:

Established by William Thomson, Lord Kelvin (1824-1907), the Kelvin scale measures temperature in relation to absolute zero, or 0K.(Units in the Kelvin system, known as Kelvins, do not include the word or symbol for degree.) The Kelvin and Celsius scales are directly related; hence, Celsius temperatures can be converted to Kelvins by adding 273.15. The Kelvin scale is used almost exclusively by scientists.

### KINETIC ENERGY:

The energy that an object possesses by virtue of its motion.

### MOLECULAR TRANSLATIONAL ENERGY:

The kinetic energy in a system produced by the movement of molecules in relation to one another.

### SYSTEM:

In physics, the term "system" usually refers to any set of physical interactions, or any material body, isolated from the rest of the universe. Anything outside of the system, including all factors and forces irrelevant to a discussion of that system, is known as the environment.

### TEMPERATURE:

A measure of the average kinetic energy—or molecular translational energy in a system. Differences in temperature determine the direction of internal energy flow between two systems when heat is being transferred.

### THERMAL ENERGY:

Heat energy, a form of kinetic energy produced by the movement of atomic or molecular particles. The greater the movement of the separticles, the greater the thermal energy.

### THERMAL EQUILIBRIUM:

The statethat exists when two systems have the same temperature. As a result, there is no exchange of heat between them.

### THERMODYNAMICS:

The study of the relationships between heat, work, and energy.

### THERMOMETRIC MEDIUM:

A substance whose properties change with temperature. A mercury or alcohol thermometer measures such changes.

### THERMOMETER:

A device that gauges temperature by measuring a temperature-dependent property, such as the expansion of a liquid in a sealed tube, or resistance to electric current.

### TRIPLE POINT:

The temperature and pressure at which a substance is at once asolid, liquid, and vapor.

### VACUUM:

Space entirely devoid of matter, including air.