# In Discussion Forum 3 Post Your Response To The Following Discussion Questions R

In Discussion Forum 3, post your response to the following discussion questions. Reply to at least two classmates’ responses by the date indicated in the course Calendar.

• Air in a cylinder is compressed to one-tenth of its original volume without change in temperature. What happens to its pressure? Imagine now that a valve is opened in order to restore the initial pressure value. What percentage of the molecules have escaped?
• Consider a 40,000 km steel pipe in the shape of a ring that fits snuggly all around the circumference of the Earth. We are heating now the ring so its temperature increased by 1 degree C. Now, the pipe will no longer be snug. How high the ring will now stand above ground level? (Make as many simplifications as necessary). Data: Coefficient of linear expansion for steel is 11*10-6 /degree C. This means, for example, that a 1-meter bar of steel that increases its temperature by 1 degree C will expand 11*10-6 meters (11 micrometers)
• Farmers resort to spraying fruit trees with water before a frost to protect the fruit from freezing. Using the concepts learned in this module, discuss why this does or does not work.
• An electric fan not only does not decrease the temperature of the air, but it actually increases air temperature. How can you then explain that you are cooled by a fan on a hot day?