Torr

A torr is a unit used to measure pressure. Pressure is the push of a force on a surface. Scientists use the torr to study very tiny amounts of pressure. It is not part of the main metric system called SI. However, people often use it with the prefix milli. This creates a smaller unit called a millitorr. One millitorr is equal to 0.001 Torr.

To understand the torr, we must look at how it works. It is based on a scale called an absolute scale. This means it has a fixed starting point. One torr is defined as exactly 1/760 of a standard atmosphere. A standard atmosphere is a set amount of pressure. That amount is 101,325 pascals. Because it uses this math, the torr stays the same everywhere. It does not change based on where you are on Earth.

This unit is named after a man named Evangelista Torricelli. He was a mathematician and a physicist from Italy. In 1644, he showed the public his first mercury barometer. A barometer is a tool used to measure air pressure. He wrote about how it worked in a letter. This letter was sent to Michelangelo Ricci on 11 June 1644. His work helped start the science of meteorology.

In the past, the torr was slightly different. People thought one torr was the same as one millimetre of mercury. This was based on the weight of mercury at 0 °C. But the weight of mercury can change with gravity. Gravity is different depending on your latitude or elevation. In 1954, scientists changed the rules for these measurements. They used the 10th General Conference on Weights and Measures to fix it. Now, the torr is a precise and clear number.

You might see different units for pressure in your life. Doctors and divers use units like centimetres of water. Weather reporters often use a unit called the bar. One bar is exactly 100,000 pascals. An atmosphere is slightly larger at 101,325 pascals. Engineers use the torr for high-vacuum physics. This is the study of spaces with almost no air. These different tools help us measure the world around us.