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Temperature

 Temperature 

What is temperature? 

Temperature can be a difficult property to define. In our everyday lives we use the word temperature to describe the hotness or coldness of an object. In physics, the temperature is the average kinetic energy of the moving particles in a substance. 

How is temperature measured? 

Temperature is measured using a thermometer. There are different scales and standards for measuring temperature including Celsius, Fahrenheit, and Kelvin. These are discussed in more detail below.

 How does a thermometer work? 

Thermometers take advantage of a scientific property called thermal expansion. Most substances will expand and take up more volume as they get hotter. Liquid thermometers have some sort of substance (this used to be mercury, but today is generally alcohol) that is enclosed in a small glass tube. As the temperature rises, the liquid expands and fills up more of the tube. When the temperature drops, the liquid contracts and takes up less of the tube. The temperature can then be read by the lines calibrated on the side of the tube. 

Temperature Scales

 There are three main temperature scales that are used today: Celsius, Fahrenheit, and Kelvin. Celsius - The most common temperature scale in the world is Celsius. Celsius uses the unit "degrees" and is abbreviated as °C. The scale sets the freezing point of water at 0 °C and the boiling point of water at 100 °C. Fahrenheit - The temperature scale most common in the United States is the Fahrenheit scale. Fahrenheit sets the freezing point of water at 32 °F and the boiling point at 212 °F. Kelvin - The standard unit of temperature that is most used by scientists is Kelvin. Kelvin doesn't use the ° symbol like the other two scales. When writing a temperature in Kelvin you just use the letter K. Kelvin uses absolute zero as the 0 point of its scale. It has the same increments as Celsius in that there are 100 increments between the freezing and boiling points of water.

 Converting Between Scales 

Celsius and Fahrenheit 

°C = (°F - 32)/1.8 

°F = 1.8 * °C + 32° 

Celsius and Kelvin

 K = °C + 273.15

 °C = K - 273.15° 

Absolute Zero 

Absolute zero is the coldest possible temperature that any substance can reach. It is equal to 0 Kelvin or -273.15 °C (-459.67°F). 

Temperature and the State of Matter 

Temperature has an effect on the state of matter. Each substance of matter will go through different phases as the temperature increases including solid, liquid, and gas. One example of this is water which changes from ice (solid) to water (liquid) to vapor (gas) as the temperature increases. You can learn more about this subject at our phases of matter page. 

Interesting Facts about Temperature 

Temperature is independent of the size or quantity of an object. 

This is called an intensive property. 

The Fahrenheit scale is named after Dutch physicist Daniel Fahrenheit. 

Temperature is a different quantity from the total amount of thermal energy in a substance, which is dependent on the size of the object. 

Celsius was named after the Swedish astronomer Anders Celsius. 

Celsius was originally known as "centigrade." 

As substances approach absolute zero they can achieve some interesting properties such as superfluidity and superconductivity.

Science of Heat

 Science of Heat

Heat is the transfer of energy from a one object to another due to a difference in temperature. Heat can be measured in joules, BTUs (British thermal unit), or calories. Heat and temperature are closely related, but they are not the same thing. The temperature of an object is determined by how fast its molecules are moving. The faster the molecules are moving the higher the temperature. We say objects that have a high temperature are hot and objects with a low temperature are cold.

 Transferring of Heat 

When two items are combined or touching each other, their molecules will transfer energy called heat. They will try to come to a point where they both have the same temperature. This is called equilibrium. Heat will flow from the hotter object to the colder. The molecules in the hotter object will slow down and the molecules in the colder object will speed up. Eventually they will get to the point where they have the same temperature. This happens all the time around you. For example, when you take an ice cube and put it into a warm soda. The ice cube will become warmer and melt, while the soda will cool down. 

Hot Objects Expand

 When something gets hotter it will expand, or get bigger. At the same time, when something gets colder it will shrink. This property is used to make mercury thermometers. The line in the thermometer is actually liquid mercury. As the liquid gets hotter, it will expand and rise in the thermometer to show a higher temperature. It's the expansion and contraction due to temperature that allows the thermometer to work.

 Heat Conduction 

When heat transfers from one object to another, this is called conduction. Some materials conduct heat better than others. Metal, for example, is a good conductor of heat. We use metal in pots and pans to cook because it will move the heat from the flame to our food quickly. Cloth, like a blanket, isn't a good conductor of heat. Because it's not a good conductor, a blanket works well to keep us warm at night as it won't conduct the heat from our bodies out to the cold air. 

Matter Changing State 

Heat has an impact on the state of matter. Matter can change state based on heat or temperature. There are three states that matter can take depending on its temperature: solid, liquid, and gas. For example, if water is cold and its molecules are moving very slow, it will be a solid (ice). If it warms up some, the ice will melt and water becomes a liquid. If you add a lot of heat to water, the molecules will move very fast and it will become a gas (steam).