# temperature

## what is temperature

No doubt you already have a good idea of what temperature is. You might say that its how warm or cool something feels. In physics, temperature is defined as the average kinetic energy of the particles of matter. When particles of matter move more quickly, they have more kinetic energy, so their temperature is higher. With a higher temperature, matter feels warmer. When particles move more slowly, they have less kinetic energy on average, so their temperature is lower. With a lower temperature, matter feels cooler.

## temperature scales

The thermometer pictured in the Figure 1.1 measures temperature on two different scales: Celsius (C) and Fahrenheit (F). Although some scientists use the Celsius scale, the SI scale for measuring temperature is the Kelvin scale. If you live in the U.S., you are probably most familiar with the Fahrenheit scale. The Table 1.1 compares all three temperature scales. Each scale uses as reference points the freezing and boiling points of water. Notice that temperatures on the Kelvin scale are not given in degrees ( ). Scale Kelvin Celsius Fahrenheit Freezing Point of Water 273 K 0 C 32 F Boiling Point of Water 373 K 100 C 212 F Because all three temperature scales are frequently used, its useful to know how to convert temperatures from one scale to another. Its easy to convert temperatures between the Kelvin and Celsius scales. Each 1-degree change on the Kelvin scale is equal to a 1-degree change on the Celsius scale. Therefore, to convert a temperature from Celsius to Kelvin, just add 273 to the Celsius temperature. For example, 10 C equals 283 Kelvin. Q: How would you convert a temperature from Kelvin to Celsius? A: You would subtract 273 from the Kelvin temperature. For example, a temperature of 300 Kevin equals 27 C. Converting between Celsius and Fahrenheit is more complicated. The following conversion factors can be used: Celsius Fahrenheit: ( C 1.8) + 32 = F Fahrenheit Celsius: ( F - 32) 1.8 = C 3. Assume that the temperature outside is 293 Kelvin but youre familiar only with the Fahrenheit scale. Do you need to wear a hat and gloves when you go outside? To find out, convert the Kelvin temperature to Fahrenheit. (Hint: Convert the Kelvin temperature to Celsius first.)

## how thermometers measure temperature

Many thermometers measure temperature with a liquid that expands when it gets warmer and contracts when it gets cooler. Look at the common household thermometer pictured in the Figure 1.1. The red liquid rises or falls in the glass tube as the temperature changes. Temperature is read off the scale at the height of the liquid in the tube. Q: Why does the liquid in the thermometer expand and contract when temperature changes? A: When the temperature is higher, particles of the liquid have greater kinetic energy, so they move about more and spread apart. This causes the liquid to expand. The opposite happens when the temperature is lower and particles of liquid have less kinetic energy. The particles move less and crowd closer together, causing the liquid to contract.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

when particles of matter move more quickly they

``````a) have more kinetic energy.

b) have a higher temperature.

c) feel warmer to the touch.

-->  d) all of the above
``````

the si scale for measuring temperature is the celsius scale.

``````a. true

-->  b. false
``````

what is the freezing point of water on the kelvin scale?

``````a) 0

b) 32

-->  c) 273

d) none of the above
``````

what is 23 c on the kelvin scale?

``````a) 150 k

b) 273 k

-->  c) 296 k

d) none of the above
``````

the temperature 10 c equals 42 f.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson