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Investigation 1 – PreLab









The Earth’s atmosphere is critical for life on our planet. It protects us from dangerous radiation from the sun and other objects coming at us from outer space, holds in surface heat and prevents it from radiating out into space, provides weather, makes flight possible, and, ultimately, allows us to talk with each other as sound waves travel through the atmosphere from one person to another. 


Meteorologists track hurricanes to alert people about its path, which could save thousands of lives.


This Investigation is designed to help you to answer the following Focus Questions:

  • What happens to air as it is heated and cooled? 
  • How do changes in the temperature of air affect its density? 
  • Why do changes in density cause air movement? 
  • How do differences in the temperature of the Earth’s atmosphere affect the movement of air? 

Note: These questions are located in your SDR at the beginning and end of the Investigation.



As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • The atmosphere is a thin layer of gases that surrounds the Earth.
  • The atmosphere consists mainly of the gases nitrogen, oxygen, and argon. Nitrogen makes up 78% of the atmosphere. Oxygen makes up 21% and argon makes up approximately 0.9% of the atmosphere.
  • The atmosphere is held in place around the Earth by Earth’s gravity.
  • The atmosphere has several layers.
  • Most of the Earth’s weather occurs in the bottom layer of the atmosphere called the troposphere.
  • The troposphere is heated by UV light and other forms of energy from the Sun which are absorbed or reflected by water and land.
  • The heat absorbed by the land or water is transferred to the air directly above the land or water by conduction and radiation. 
  • All areas of the Earth do not receive the same amount of light and other electromagnetic radiation.
  • Because the Earth is tilted 23.5º on its axis, the angle at which light hits the equator is more direct than the areas away from the equator.
  • The north and south poles receive the least amount of direct light.
  • Differences in the amount of direct light cause differences in the amount of heat. More direct light results in more heat that is received. Less direct light results in less heat that is received. 
  • Gases behave in certain, predictable ways. One of the ways in which gases behave is described by the scientific principle known as Charles’ Law.
  • Charles’ Law describes how the volume changes with changes in temperature when the pressure of a gas is constant; as the temperature of a gas increases, the volume of the gas increases.



The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • density
  • atmosphere
  • Charles’ Law
  • troposphere

Note: Definitions of these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.



  • The focus of this Investigation is to better understand the changes that can occur to the atmosphere and how these changes result in changes in the weather.
  • The changes in weather that will be examined are the temperature, pressure, and precipitation received by different areas on Earth.
  • Even at this early point in the CELL, you already have gained knowledge about the atmosphere. Consider what you have already learned in answering the following questions:
    • What does someone mean when they talk about “the weather?”
    • What causes weather?
    • Where is the atmosphere and what is its composition?
    • Are all areas of the atmosphere the same?
  • Review what you already know about temperature and precipitation.
  • Think about the relationship between temperature and kinetic energy.

Note: You should be thinking in terms that temperature as a measure of the kinetic energy of the molecules of a solid, liquid, or gas. In addition, you should generate ideas about precipitation that include: precipitation as part of the water cycle, and precipitation occurs in solid and liquid forms such as rain, snow, hail, freezing rain, and sleet.

  • Explore and evaluate your current ideas about pressure. Think of pressure as the force exerted per area of an object or substance.
  • One type of pressure, atmospheric pressure. Its relationship to weather changes will be discussed further during Investigation Two.
  • You will begin your exploration of the atmosphere and weather by focusing on the changes that occur to air as it is heated and cooled.
  • Look at the Focus Questions again. Think about which physical characteristics of air you should focus on as you conduct your experiments. Note that the Focus Questions make reference to temperature and density, therefore you should think about the changes in temperature and density that may occur to air.
  • Keep the following questions in mind as you enter the lab for Investigation 1 experiments. You will be able to formulate answers to these questions after you have completed the Investigation.
    • Where does weather occur? 
    • What is density? How is it calculated?
    • How do fluids of different densities behave when mixed together? 
    • How do changes in the atmosphere cause changes in the weather?
  • Briefly review the concept of density:
    • The density of a substance is a measure of the amount of matter contained within a certain volume of that substance.
    • Remember, the formula for calculating density is: Density= mass/volume
    • Consider what you already know about the density of liquids. Remember that if immiscible liquids of two different densities are combined, the more dense liquid will sink below the less dense liquid.
  • Liquids have certain ways in which they respond to changes in some of their physical characteristics such as density and response to a force. Because of these ways, scientists refer to liquids as fluids. Scientists also consider gases such as “air” fluids.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.



You should review the Investigation and video in preparation for the Lab.