Explore the concept of temperature. Learn the definition of temperature, see its unit, and understand how it is measured. Discover examples of temperature.
Updated: 11/21/2023
Temperature Definition, Measurement & Examples
Table of Contents
- What is Temperature?
- What Does Temperature Measure?
- Temperature Measurement
- Relation Between Temperature and Kinetic Energy
- Examples of Temperature
- Lesson Summary
- FAQs
- Activities
Temperature
How much kinetic energy are in the molecules of a substance determines its temperature. Cold is not a measurable quantity, but heat is therefore if something is cold we could say it lacks enough heat. Let's do an activity where we take multiple measurements of water as it is heating up to its boiling point.
Activity
We are going to measure the temperature of water from room temperature to its boiling point. Be sure to have a responsible adult supervisor you while doing this activity as water being heated can cause burns if it splashes or spills on you.
Equipment
- Container of water in a pot or beaker
- Enough water to half-way fill the pot or beaker
- Stove or Bunsen burner
- Striker if using Bunsen burner
- Ring stand with platform is the beaker is being used
- Thermometer
- Stopwatch
- Paper and pen
Procedure
- Put the water into the pot or beaker.
- Put the beaker on the ring stand platform and the Bunser burner underneath it or put the pot on the stove.
- Attach the thermometer to the pan or in the beaker so that it is secure.
- Record the temperature
- Light the Bunsen burner or turn on the stove to high.
- Take temperature measurements every 1 minute.
Post-activity questions
- What is happening to the molecules of water when the mass of water is being heated?
- Plot the temperature versus time data. Is the graph linear or quadratic?
Solutions
- The molecules are absorbing heat energy and therefore are moving faster and faster.
- The graph should be linear.
What are the units of measure for temperature?
There are multiple units of measurement for temperature. Fahrenheit and Celcius are commonly used to describe temperature. Kelvin is a unit of temperature often used in scientific settings.
How are temperatures measured?
Temperatures are measured with the use of thermometers. There are multiple types of thermometers, including liquid, infrared, and digital thermometers. Because of their potential danger, liquid thermometers are mainly unused today.
What does temperature actually measure?
Temperature is a quantifiable way to describe the warmth or coolness of a substance. It measures the average kinetic energy of that substance.
Table of Contents
- What is Temperature?
- What Does Temperature Measure?
- Temperature Measurement
- Relation Between Temperature and Kinetic Energy
- Examples of Temperature
- Lesson Summary
Rebecca is enjoying a vacation retreat with some of her closest friends. After a day of hiking through a natural forest, they are cozied up under blankets around a roaring fire as fluffy flakes of snow descend around them. One can imagine the "warmth" underneath the blankets or on their cheeks from the nearby flames. The snow falling around them is recognizably "cold."
While these descriptive terms are familiar and appropriate to describe this scene, they're a poor representation of temperature. Temperature, by definition, is a way to describe warmth and coldness using quantitative descriptors. That is, it's able to add a comparative, numeric value to an otherwise subjective descriptor.
Consider for a moment if someone were to say, "it's cold outside." What does the term "cold" in this sentence really mean? It could mean that there's a slight chill, or it could mean there's a blizzard taking place. Instead, imagine someone were to say, "it's in the '60s outside." By doing this, they're assigning a rough temperature to the situation. While snow gear isn't appropriate, one may now gauge that a light jacket may be warranted.
It's important to denote that temperature and heat are not the same. The term "heat" is used to describe an amount of energy. Consider the camping retreat scene from the first paragraph again. Heat is what emanates from the fire, while temperature is the numeric value measured on nearby surfaces. Another way to think of it is that it takes heat to raise the temperature. For instance, it takes about 4.2 joules of heat to raise water temperature by 1 degree Celsius.
Notice that the temperature quantity given here is "Celsius." Multiple types of units can describe temperature. The public commonly uses Celsius and Fahrenheit. Kelvin is often used in a scientific setting.
In this lesson, investigate temperature in more detail to answer the following questions:
- How can temperature be measured?
- What is the relationship between temperature and kinetic energy?
- What are the units for temperature, and how can they be converted?
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Previously, this lesson mentioned that temperature is a quantitative measurement to describe the degree of warmth or coolness. But what does temperature measure specifically? Temperature is measuring the average kinetic energy within a system. Kinetic energy is the energy of motion. The particles that make up all matter in the universe are constantly in motion. While this may be easy to picture with fluid substances, such as water or air, even the particles that compose solid, non-flowing objects are in some degree of movement.
Temperature is thus describing the average movement of particles within a system. As the speed of particles increases, so does the temperature. Temperature's relation to kinetic energy is discussed in more detail below.
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Temperature is often measured with the use of a thermometer. To understand how thermometers work, one must first understand the concept of thermal equilibrium. When two touching substances are at the same temperature, they are in thermal equilibrium. When they are not, heat from the hotter substance is transferred to the cooler substance until thermal equilibrium is met. The liquid inside of a thermometer must come into thermal equilibrium with the substance it is placed against. As the temperature of the liquid within the thermometer rises, it undergoes thermal expansion, a phenomenon where the volume of a substance increases as its temperature increases. Once thermal equilibrium is achieved, the degree of expansion can be compared to the scale on the thermometer to describe the temperature in degrees.
Liquid thermometers often contain mercury, which is a toxic substance or alcohol. As thermometers were made of glass and could often break, liquid-based thermometers have mainly been phased out. The thermometers commonly used today measure temperature digitally with either heat sensors or infrared. Thermostats utilize electronic thermometers to detect the change in temperature of a room or building. When the temperature rises above or falls below a desired threshold, thermostats kick on central cooling or heating to bring the temperature back to the desired level.
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Temperature is a measurement of the average kinetic energy of a substance. When kinetic energy is high, particles move quickly. This correlates to higher temperatures. When molecules are moving slowly, temperatures are cooler. Heated particles that are moving faster expand, and cooled particles compress together. Thus, temperature and volume are related because of the properties of kinetic energy.
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Examples are often the best way to truly understand a concept. Below, explore two examples of temperatures, including:
- A real-world example of changing temperature on bridge construction
- Methods of unit conversion
Example of Changing Temperature
Recall that when substances increase in volume when their temperature increases. Engineers must consider thermal expansion when creating structures, especially if those structures may be exposed to changing temperatures that come with seasonal shifts. Bridges are often exposed to changing temperatures and may become damaged if thermal expansion is not considered during their construction. To solve the issues of growing and shrinking material, many engineers will design thermal expansion joints within bridges. These are intentional gaps that are left so that as temperatures increases, the bridge can move slightly without cracking.
Example of Temperature Conversion
The temperature has multiple units of measurement. While all measurements can be used appropriately, different areas and cultures use different units of measurement as their standard descriptors. For instance, Fahrenheit is commonly used within the United States, while many European countries use Celsius. There are simple equations that can be used to convert these values. Consider a citizen in the United States who stated it was 56 degrees Fahrenheit outside over the phone to their friend in England. The conversion equation between these two units is provided below:
{eq}C=(F-32)*\frac{5}{9} {/eq}
Based on this equation, 56 degrees in Fahrenheit is equivalent to roughly 13.3 degrees in Celsius, as seen below:
{eq}C=(56-32)*\frac{5}{9} {/eq}
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Temperature is a quantifiable way to describe the warmth or coolness of a substance. It is also the measure of the average kinetic energy of a substance. Kinetic energy is the energy of movement. When particles within a substance are moving quickly, kinetic energy is high. When particles are moving slowly, kinetic energy is low. Temperature and heat are not the same, as heat is the amount of heat energy that a substance gives off.
Thermal equilibrium occurs when two substances that are touching are of the same temperature. When two substances are not at the same temperature, heat from one substance is transferred to the cooler substance until thermal equilibrium is achieved. This is the mechanism behind a liquid thermometer, which typically utilizes the expansion of alcohol or mercury to estimate temperature. Thermal expansion states that as the temperature of a substance rises, so too does its volume. Because of this, engineers must consider ways to construct structures that account for the shrinking and growth of material.
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Video Transcript
Temperature Defined
Temperature is a measure of how hot or cold something is; specifically, a measure of the average kinetic energy of the particles in an object, which is a type of energy associated with motion. But how hot is hot, and how cold is cold? The terms hot and cold are not very scientific terms. If we really want to specify how hot or cold something is, we must use temperature. For instance, how hot is melted iron? To answer that question, a physical scientist would measure the temperature of the liquid metal. Using temperature instead of words, like hot or cold, reduces confusion.
Temperature Depends on the Kinetic Energy of Particles
All matter is made of particles - atoms or molecules - that are in constant motion. Because the particles are in motion, they have kinetic energy. The faster the particles are moving, the more kinetic energy they have. What does temperature have to do with kinetic energy? Well, as described in this figure, the more kinetic energy the particles of an object have, the higher is the temperature of the object.
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Temperature is an average measure. Particles of matter are constantly moving, but they don't all move at the same speed and in the same direction all the time. As we can see in this figure, the motion of the particles is random. The particles of matter in an object move in different directions, and some particles move faster than others. As a result, some particles have more kinetic energy than others. So what determines an object's temperature? An object's temperature is the best approximation of the kinetic energy of the particles. When we measure an object's temperature, we measure the average kinetic energy of the particles in the object.
The higher the temperature, the faster the molecules of the substance move, on the average. Dyes will spread more rapidly through hot water than cold water. This is because of the increased motion of the molecules. Temperature does not have to do with the number of molecules involved. Under given conditions, the temperatures of 10-ml and 100-ml samples of boiling water are equal. This means that the average kinetic energy of the molecules is the same for the two different quantities of water.
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In this image, there is more tea in the teapot than in the mug, but the temperature of the tea in the mug is the same as the temperature of the tea in the teapot.
Measuring Temperature
Since molecules are so small, you must use an indirect method to measure the kinetic energy of the molecules of a substance. As heat is added to a substance, the molecules move more rapidly. This increased motion causes a small increase in the volume, or amount of space, taken up by most materials. There are devices that use the expansion of a substance to give an indirect measure of temperature. Such devices are called thermometers.
There are many types of thermometers. Many thermometers are thin glass tubes filled with a liquid. Mercury and alcohol are often used in thermometers because they remain liquids over a large temperature range. A change in temperature causes a small change in the volume of the liquid. However, this effect is magnified when the liquid expands in the very thin tube of the thermometer.
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Some thermometers involve the use of bimetal strips. In such thermometers, strips made of two different metals are bonded or glued together. Because the metals expand at different rates, the combined strip bends in a certain direction when it is heated. When it cools, it bends in the opposite direction. The figure below shows a bimetal strip used as a thermostat. A thermostat is a device used to control heating and cooling systems.
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Some thermometers, often used on the outside of aquariums, contain liquid crystals that change color based on temperature. As temperature increases, the molecules of the liquid crystal bump into each other more and more. This causes a change in the structure of the crystals, which in turn affects their color. These thermometers are able to accurately determine the temperature between 65 F and 85 F.
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A thermometer with no marks, or graduations, would not be very useful to you. A thermometer is calibrated by marking two fixed points. The space between these fixed points is broken up into divisions called degrees. Degrees are used to indicate temperature. There are three types of temperature scales commonly used today: Celsius, Fahrenheit, and Kelvin. We are used to expressing temperature with degrees Fahrenheit (F). Scientists often use degrees Celsius (C), but the Kelvin (K) is the SI unit for temperature.
Thermometers can measure temperature because of thermal expansion. Thermal expansion is the increase in volume of a substance due to an increase in temperature. As a substance gets hotter, its particles move faster. The particles themselves do not expand; they just spread out so that the entire substance expands. Different substances expand by different amounts for a given temperature change. When you insert a thermometer into a hot substance, the liquid inside the thermometer expands and rises. You measure the temperature of a substance by measuring the expansion of the liquid in the thermometer.
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Thermal and Kinetic Energy
Atoms are always in motion. Imagine you had a microscope powerful enough to see individual molecules in a compound (or atoms in the case of an element). You would see that the molecules are in constant motion, even in a solid object. In a solid, the molecules are not fixed in place, but act like they are connected by springs as shown here:
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Each molecule stays in the same average place, but constantly jiggles back and forth in all directions. As you might guess, the 'jiggling' means motion, and motion means energy. This 'jiggling' is caused by thermal energy, which is a kind of kinetic energy.
Thermal energy is proportional to temperature; when the temperature goes up, the energy of motion increases. That means the molecules 'jiggle' around more vigorously. The higher the temperature, the more thermal energy molecules have and the faster they move around. Temperature measures a particular kind of kinetic energy per molecule.
When the molecules of a substance absorb energy, they tend to move faster. A molecule moves more rapidly if it has more kinetic energy. If you throw a rock, the rock gets more kinetic energy, but the temperature of the rock does not go up. How can temperature measure kinetic energy then? The answer is the difference between random motion of the molecules and average motion of the object. For a collection of many molecules (like a rock), the kinetic energy has two parts. The kinetic energy of the thrown rock comes from the average motion of the whole collection, the whole rock. This kinetic energy is not what temperature measures.
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Each molecule in the rock is also 'jiggling' back and forth independently of the other molecules in the rock. This 'jiggling' motion is random motion. On average, there are as many molecules moving one way as there are moving the opposite way. Temperature measures the kinetic energy of the random motion. Temperature is not affected by any kinetic energy associated with average motion. That is why throwing a rock does not make it hotter.
Example of Temperature
Let's learn more about temperature and thermal expansion with an example. Have you ever gone across a highway bridge in a car? You probably heard and felt a 'thuh-thunk' every couple of seconds as you went over the bridge. That sound occurs when the car goes over small gaps called expansion joints.
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The concrete segments of a bridge can expand on hot days. When the temperature drops, the segments contract. These joints keep the bridge from buckling as a result of thermal expansion. Recall that thermal expansion is the increase in volume of a substance due to an increase in temperature.
Lesson Summary
Heat and temperature are related, but not the same. Temperature is a measure of the average kinetic energy of the particles of a substance. The higher the temperature of an object, the higher is its kinetic energy. Kinetic energy is a type of energy associated with motion. Temperature is measured with thermometers, which are devices that use the expansion of a substance to give an indirect measure of temperature. The units that are used to measure temperature are called degrees. When temperature increases in an object, the molecules inside it start to move faster, and this causes the object to expand. Thermal expansion is the increase in volume of a substance due to an increase in temperature.
Learning Outcomes
Once you've completed this lesson, you should be able to:
- Define temperature
- Explain the relationship between temperature and kinetic energy
- Describe how temperature is measured
- Recall how thermal expansion occurs
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