Friday, May 12, 2017

Clockwise and Counter-Clockwise

Many folks have heard the phrase “righty tighty, lefty loosey.” This little limerick is a clever way of remembering which way traditional right-handed threads turn. However, it can be misleading. The right or left direction refers to the direction the top of the circle will turn. But the bottom of the circle turns in the opposite direction. So while the top is being turned to the right, the bottom is being turned to the left.

I really prefer the terms clockwise and counter-clockwise to describe rotational movement because you don’t have to be concerned if you’ re looking at the top of the circle or the bottom. You only have to remember which way a clock hand moves. Therein lies the problem. In today’s digital age, some people can’t tell you which way a clock hand moves because they rarely see one.

Every program should have an operating analog clock in the class room so students can learn the difference between clockwise and counterclockwise. Notice how the numbers on the clock face progress from the top to the right, creating clockwise motion. Logically, counter-clockwise motion is the opposite.

This little saying also ignores the left handed threads, which are exactly backwards from right-hand threads. Although far less common, left hand threads are often found on connections for flammable gas, such as the regulators and hoses used for Acetylene on an oxy-acetylene torch. In that case it is “righty loose, lefty tighty.” Doesn’t have quite the same ring to it. Left hand threads on torches have a hash mark on them to indicate that they are left-hand threads. The acetylene and oxygen have opposite threads for a reason – to prevent mixing up the regulators and hoses. Mixing the gasses under pressure can create a combustible mixture.

1 comment:

  1. I had a student who, bless his heart, could not grasp which way to open a valve or turn it off. I finally took him outside, sat a chair by a hose bib and said "Turn this water valve on and off 100 times and then come back in and see me." The next day, he still couldn't do it.