Review of Energy and Density

Understanding heat and density will help us to understand  how changes happen in and around the Earth.   Review some important ideas and activities involving energy and density.

Question:  What are some different forms of energy?

• Solar/heat energy - drives winds, storms, and ocean currents.
• Chemical energy - important in food chains and energy transfer within the biosphere.
• Mechanical energy - a factor in the mechanical weathering of rock into fragments of loose material that often leads to rockfalls and landslides.
• Gravitational Energy -  the force of attraction between objects due to their mass. This controls rainfall, snowfall, landslides, movement of water downhill, etc.
• Kinetic energy - energy associated with motion.
• Potential energy - stored energy ready to be released and converted to other forms of energy, such as kinetic.

    Heat is a form of energy produced by different sources. 
    Sources of heat include:

• the sun
• the Earthís core
• chemical reactions
• radioactivity
• friction

Question:  What happens when the amount of heat changes? 

    A. Adding heat:

• causes molecules to move more quickly to most liquids and gases
• causes them to expand - become less dense

• causes molecules to move more slowly from most liquids and gases
• causes them to contract ? become more dense 

Question:  How does heat travel? 

    A. Conduction

• Heat travels differently through materials by conduction.
• Some materials are better conductors than others.
• The transfer of heat by direct contact of particles of matter causes molecules to move more quickly. 

     B. Convection

• Heat travels through fluids by convection.
• The transfer of heat between warmer and cooler gases and liquids creates currents. 

Question:  What is density? 

• In simple language:  the amount of ìstuffî in a given space.
• More scientifically,  density = mass/volume;  a measure of how much mass there is per volume.

Question: How does temperature affect density? 

• When a liquid or gas is heated, the molecules move faster, bump into each other, and spread apart. Because the molecules are spread apart, they take up more space. They are less dense.
• The opposite occurs when a liquid or gas is cooled. The molecules move more slowly and take  up less space.
• Therefore temperature can affect density. 

 Question:  How can we use density to explain why some things float and others sink? 

• Each substance has its own density, based upon the amount of mass per volume.
• Water has a density of one.
• Liquids and solids with a density greater than one will sink.
• Liquids and solids with a density less than one will float

Activities

Heat Energy:  Feel where the heat is
Heat Energy:  Compare hot and cold molecules
Heat and Density:  Moving marbles molecules
Density:   Stuffing a box with crumpled paper
Density:  Density Animations

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