Laws of Physics

# What is a physical quantity

Physical quantities are used to describe the quantitative properties of physical objects, phenomena, and processes.

When studying physical bodies, phenomena, and processes, it is necessary to somehow record their characteristics (properties, signs). At the same time, the characteristics can be not only qualitative (for example, the body falls, the gas expands, etc.), but also quantitative (at what speed the body falls, what volume the gas occupied, what mass the body has, what is the length of the trajectory, etc.). P.).

You may need to learn Sound and light waves.

So physical quantities are length, width, height, mass, volume, speed, time, acceleration, area, etc.

Physical quantities in each case have their own meanings. So the speed of one body can be 10 km/h, and the speed of another can be equal to 20 km/h. Here we have the same physical quantity – speed.

However, its meanings are different. Thus, the same physical quantity can describe different physical bodies, phenomena, and processes.

In physics, for each physical quantity, its own designation is introduced, most often expressed in one English letter. At the same time, there are cases when in different sections of physics the same letter can mean different things. For example, v stands for speed and V stands for volume.

The value of physical quantities is always expressed in some units of measurement. In other words, the value of a physical quantity is a named number. So mass can be expressed in kilograms, grams, tons, etc.; time – in hours, minutes, years, etc.

Throughout history, different countries and parts of the world have developed their own units of measurement. So, for example, it is customary for us to measure distance in kilometers, and in the USA – in miles. To avoid confusion, the International System of Units (SI) was introduced.It is she who is used in physics when measuring the values ​​of physical quantities. In the international system of units, length is measured in meters, time in seconds, and mass in kilograms. The designation of these quantities, respectively, is “m”, “s”, and “kg”.

It happens that the value of a physical quantity is very large or very small. In this case, division or multiplication by 10, 100, 1000, etc. is performed, and a special prefix is ​​added to the name of the unit of measurement.

For example: 1000 meters = 1 kilometer, 1000 grams = 1 kilogram.

The prefix “kilo” is used here. But in “60 seconds = 1 minute” each dimension has its own name (this is an exception)