Earth Science Activities Using a Sling Psychrometer

By Sean Tvelia

A sling psychrometer is a tool used to measure relative humidity. Find out about an earth science activity using a sling with help from an Associate Professor of Geology at Suffolk County Community College in this free video clip.


Hi, I'm Sean Tvelia. We're here at Suffolk County Community College to talk about a simple project involving a sling psychrometer. A sling psychrometer is a tool used to measure relative humidity. Now, relative humidity is actually a ratio of the percent moisture in the air versus the saturation level, or the maximum amount of moisture that could be contained in the air at a given temperature. A sling psychrometer has a number of components, the first component is a sling which houses two thermometers. In this case we have two mercury thermometers, the first one is a dry bulb that simply measures the temperature of the air, and as you can see today it is 73 degrees. And then we have a wet bulb. The wet bulb always has a cloth at the end and will be slightly moistened. And then we have the sling that they are attached to that allows us to spin the sling psychrometer. Now, the way this works, once the wet bulb is wet, we will sling the psychrometer around, and some of the moisture will evaporate from the cloth and lower the temperature on the wet bulb, and then all we need to do is measure the change in temperature on the wet bulb and locate that difference of where that difference in temperature from the wet bulb on a chart of relative humidity based on the temperature of the room, and we can easily determine the relative humidity on that day in that location. So one really simple project involving a sling psychrometer is to measure the relative humidity versus the temperature on a daily basis, and we can produce a plot showing how relative humidity changes with respect to temperature.