Temperature and Thermal Equilibrium Chapter 8: Section 1

Learning Targets Define the word temperature Describe how a thermometer works Explain the difference between the three major temperature scales

Defining Temperature When we touch an ice cube we feel a sensation that would be described as “cold.” Likewise, we experience a “hot” feeling when we grab a mug of coffee Our sense of touch is a qualitative indicator of temperature but this sensation of hot or cold also depends on the temperature of our skin

What is Temperature? Adding or removing energy usually changes temperature In this sense, temperature is a measure of the amount of kinetic energy in an object.

Simply put, temperature is what a thermometer reads When heat (energy) is introduced into a system, molecules move faster and begin to bump into each other harder and more often. The measure of the energy of these collisions is temperature. Simply put, temperature is what a thermometer reads

Thermal Equilibrium When two objects with different temperatures are in contact, both will eventually reach the same temperature and heat transfer will cease At this point the objects are said to have reached thermal equilibrium.

How Thermometers Work Liquid thermometers are based on the principal of thermal expansion. When a substance gets hotter, it expands Because the liquid is enclosed in a tall, narrow column, the increase in volume causes a change in the height of the liquid within the column. The increase in volume, and thus the height of the liquid column, is proportional to the increase in temperature.

Temperature Scales The Celsius Scale A Celsius thermometer has 100 equal divisions between the normal freezing point and the normal boiling point of water. The Celsius scale is used in countries that have adopted the metric system and in the scientific community

The Fahrenheit Scale The United States more commonly uses the Fahrenheit temperature scale. The normal freezing point of water is designated as 32 degrees and the normal boiling point of water is 212 degrees.

Celsius- Fahrenheit Conversions

The Kelvin Scale The Kelvin temperature scale is the most widely used temperature scale among scientists. There are only positive values on the Kelvin Scale

Absolute Zero The zero point on the Kelvin scale is known as absolute zero. It is the lowest temperature that can theoretically be achieved. Scientists and engineers have been able to cool matter down to temperatures close to -273°C, but never below it.