Understanding Time, Temperature, and Pressure Measurement
Time
Time is a scale that characterizes the length of a phenomenon and a certain moment in the course of events. It has a vital role as a magnitude, such as length and mass. However, measuring time presents some difficulties due to its intangible nature. For this reason, time is often associated with a clock hand, the displacement of a shadow, etc.
Temperature
Heat and Temperature
Mayer’s experiments finally led to Joule’s conclusion that heat is one more way to demonstrate energy. Thus, heat can be transformed into mechanical energy, electrochemical energy, etc.
The heat or thermal energy of a body is the sum of the kinetic energy of all the particles that form it. It depends on the body’s mass and the characteristics of the body in question.
Body temperature is the average value of thermal energy that corresponds to each particle of the body. The temperature does not depend on the mass or characteristics of the body.
Thermometers
Thermometers are instruments used to measure temperature. They are very numerous and can be classified according to the property on which their way of measuring is based (gas resistance, thermocouples, pyrometers, acoustic, magnetic, liquid expansion, etc.).
Liquid expansion is the most commonly employed method in laboratories and in everyday life. A liquid encased in a glass or quartz enclosure expands when heated and rises through a capillary tube of constant section.
The sensitivity of the instrument is a function of the relative size of the deposit or bulb and capillary, and in the best conditions, it can appreciate thousandths of a Kelvin. Mercury thermometers have considerable advantages over those made with other liquids: mercury does not wet the glass and can be obtained in a very pure state.
Thermometer Classification
- By way of capillary and scale: Hollow rod thermometers and massive thermometers
- By type of setting: Thermometers with adjustable grinding or Quickfit closure
- Special thermometers: These models can, besides current temperature readings, take readings of maximum and minimum temperatures recorded over a period of time. They consist of a U-shaped glass tube provided with two swellings at the ends, which contain alcohol instead of mercury. One widening is filled with alcohol, while the other is not. Mercury fills the central part of the apparatus.
Gas Pressure
Gas pressure is the force exerted by the gas against the walls of the enclosure it completely fills.
Barometers
Barometers are instruments for measuring atmospheric pressure.
Mercury Barometer
A mercury barometer consists of a glass tube closed at one end and open at the bottom, which is provided with a curved needle to adjust the level of mercury. When placed in the vertical position, the mercury in the tube falls to a height above the level of the container, leaving a nearly perfect vacuum at the top of the tube.
In the Fortin barometer, the barometer tube is introduced into a tank that has a membrane and a screw to adjust the level of mercury in the container using an ivory pointer.
Corrections
- Correction for temperature or barometric height reduction at 0°C: The temperature is read on an additional thermometer, and the correction table is consulted (Annex 1).
- Correction for latitude: Due to the difference in gravity, a correction is made using the table in Annex 2. If the latitude is less than 45º, subtract the corresponding millimeters from the barometric altitude corrected to 0°C based on latitude. If the latitude is greater than 45º, add the corresponding value.