Newtonian Cooling and Adiabatic Index of Air

This experiment consists of two components, Parts A and B.

Part A: Newtonian Cooling

In part A the student investigates how a body cools in air, and in particular calculate the thickness of the boundary layer of air that surrounds the body. This is another example of Newtonian cooling, the first being explored in a first year experiment. In this experiment the boundary layer is explored more throughly and the size of the boundary layer calculated. The equipment in this experiment has also been used before in a first year experiment, a calorimeter. This experiment builds on skills the students have already developed by shows students that collecting data is not the the most important part if an experiment. The goal of the experiment is often carried out by analysing the data and that the same experiment can be used to prove multiple hypothesis. 

 

You can try this lab out yourself with theis simulation / online lab: The Newton's Law of Cooling

Calorimeter used in Part A Apparatus used in Part B

Part B: Adiabatic Index of Air

In part B the student measures the index of air using a particularly elegant method. This property of air has also been explored before in another first year experiment.  

The apparatus used consists of a large vessel into which a long vertical transparent tube is fitted. The diameter of the tube is such that a steel ball (or cylinder, depending on the version of the apparatus you are using) just fits into the tube. This allows the ball to move freely in the tube but it is such a good fit that the air below the steel ball/cylinder cannot flow past it. As such the the air in the vessel and lower part of the tube is nearly isolated from the outside atmosphere after the ball is inserted. This similar to a plug in the sink. While water, like air, seems that it cann slip through any gap if the plug is the right size it can fit into the drain and stop water flowing around it and down the drain. 

As such when the steel ball/cylinder is dropped down the tube it falls due to gravity and it "pushes" the air below it down, compressing the air. Much like a spring the air will them "push" back to resturn to it's original size causing the steel ball/cylider to slow down and then travel back up the tube. The time for the steel ball/cylinder to go up and down a number of times is recorded. A good explanation of the equations involved in calculating the adiabatic index of air using this method can be found here

If you wish to try this experiment yourself you can collect data from this YouTube video using this guide to the calculations.

Department of Physics

Roinn na Fisice

Room 213 (Physics Office), 2nd floor, Kane Science Building, University College Cork, Ireland.,

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