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Kinetic-Molecular Theory

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It's Getting Crowded

It's Getting Crowded

Credit: Jirka Matousek
Source: http://www.flickr.com/photos/28415633@N00/9101831606
License: CC BY-NC 3.0

Crowds can be enjoyable or intimidating. For the enthusiastic “people-person”, crowds are lively, exciting, and fun. On the other hand, those who experience agoraphobia (fear of public places) or haphephobia (fear of being touched) don’t deal well with crowds. These people much prefer a considerably less populated environment. Even presumably “normal” individuals at times need a little space.

News You Can Use

  • A crowded dance floor makes it challenging to really do fancy steps. Too many people too close together means there are a lot of collisions. Most of the time a bump doesn’t create any problems, but occasionally a collision between two couples can be harder than usual. The more active the dancing (rock and roll, for example, rather than the waltz), the more frequent the possibility of bumping into someone else.
  • The kinetic-molecular theory is easiest to apply to gases. Each gas particle is considered to be independent of all other gas particles. Unlike couples on the dance floor, a gas particle that collides with another gas particle just bounces off with no change in speed, just direction. Gas particles don’t respond to heat the same way people do. When we get hot, we become less active and just want to sit in the shade with a cool drink of water or soda. When gas molecules experience an increase in temperature, they get excited and move faster. No cool drink for them.
  • Credit: dfbphotos
    Source: http://www.flickr.com/photos/dfb_photos/5998405761/
    License: CC BY-NC 3.0

    Hot air balloons work under the same principle. Air molecules heat up and start rising, colliding with the inside of the balloon to push it up into the air [Figure2]


  • How we talk about gas pressure varies from group to group. Barometric pressure in weather reports in the U.S are given in inches of mercury while air pressures high in the air are given in millibars or hectopascals. International preference is strongly moving toward hectopascals since this is a direct measurement.
  • Watch a video about the kinetic-molecular theory at the link below: https://www.youtube.com/watch?v=Y8j6peP5nNg

Show What You Know

Use the links below to learn more about the kinetic-molecular theory.  Then answer the following questions.

  1. What is a law? a theory?
  2. Who first began to develop he kinetic-molecular theory?
  3. What do we assume about the volume of gas particles?
  4. How is pressure defined?
  5. What happens to barometric pressure during stormy weather?
  6. Where is barometric pressure plotted for weather forecasting?

Image Attributions

  1. [1]^ Credit: Jirka Matousek; Source: http://www.flickr.com/photos/28415633@N00/9101831606; License: CC BY-NC 3.0
  2. [2]^ Credit: dfbphotos; Source: http://www.flickr.com/photos/dfb_photos/5998405761/; License: CC BY-NC 3.0

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