Материал готовится,

пожалуйста, возвращайтесь позднее

пожалуйста, возвращайтесь позднее

Mass, length, time, area, velocity, acceleration - all of these are physical quantities.

Whenever we measure one of these we are finding its magnitude. To find a

magnitude of a physical quantity we must measure it. The magnitude of any

physical quantity is expressed as number times a unit of measure.

Time is a physical concept and its definition is related to certain laws of physics.

The laws of physics say that the average time it takes for the sun to move from its

noon position on one day to its noon position the next day must be constant and is

called the mean solar day. The laws of physics say also that the period of

oscillation of a vibrating slab of crystal in a crystal oscillator should remain

constant if the temperature and other external conditions are kept constant. So an

electronic crystal oscillator can be made into a very accurate clock. The same is

true of the vibrational frequency of atoms in a molecule. In fact atomic clocks

counting up these vibrations are the most accurate of all.

The basic unit of time used in both the English and the metric systems is the

second, the latter being 1/60 x 1/60 x 1/24 = 1/86.400 of a mean solar day. That is

why we divide the mean solar day into 86.400 equal parts to get the unit used to

measure time, namely 1 second.

A concept such as time basing on the laws of physics, we cannot be sure that these

laws are absolutely correct. For example, suppose the speed of light is slowly

increasing with the time. This would then cause a change in some of our standards

of length and time. So far there is no experimental evidence that any of the

universal physical constants is changing with time, this does not rule out the

possibility of a very slow change beyond the accuracy of present measurements.

Being also a physical concept mass must be defined in terms of certain laws of

physics. In the metric system the unit of mass was originally defined as the amount

of mass contained in 1 cc (cubic centimeter) of water (at a specified temperature

and pressure), this amount of mass-being called the gram. Thus the density of

water is conveniently one gram per cubic centimeter. Jn the English system the

unit of mass is the pound, one kilogram (10’ grams) being equal to 2.204 pounds

of mass. We will use the abbreviations gm for gram, kg for kilogram and lb for

pound. In physics the quantities such as force and energy are usually measured

either In meters, kilograms, and seconds or in centimeters, grams and seconds, the

former being called the MKS system of units and the latter the CGS system of

unite). Both of these metric systems are referred to in scientific papers.

Whenever we measure one of these we are finding its magnitude. To find a

magnitude of a physical quantity we must measure it. The magnitude of any

physical quantity is expressed as number times a unit of measure.

Time is a physical concept and its definition is related to certain laws of physics.

The laws of physics say that the average time it takes for the sun to move from its

noon position on one day to its noon position the next day must be constant and is

called the mean solar day. The laws of physics say also that the period of

oscillation of a vibrating slab of crystal in a crystal oscillator should remain

constant if the temperature and other external conditions are kept constant. So an

electronic crystal oscillator can be made into a very accurate clock. The same is

true of the vibrational frequency of atoms in a molecule. In fact atomic clocks

counting up these vibrations are the most accurate of all.

The basic unit of time used in both the English and the metric systems is the

second, the latter being 1/60 x 1/60 x 1/24 = 1/86.400 of a mean solar day. That is

why we divide the mean solar day into 86.400 equal parts to get the unit used to

measure time, namely 1 second.

A concept such as time basing on the laws of physics, we cannot be sure that these

laws are absolutely correct. For example, suppose the speed of light is slowly

increasing with the time. This would then cause a change in some of our standards

of length and time. So far there is no experimental evidence that any of the

universal physical constants is changing with time, this does not rule out the

possibility of a very slow change beyond the accuracy of present measurements.

Being also a physical concept mass must be defined in terms of certain laws of

physics. In the metric system the unit of mass was originally defined as the amount

of mass contained in 1 cc (cubic centimeter) of water (at a specified temperature

and pressure), this amount of mass-being called the gram. Thus the density of

water is conveniently one gram per cubic centimeter. Jn the English system the

unit of mass is the pound, one kilogram (10’ grams) being equal to 2.204 pounds

of mass. We will use the abbreviations gm for gram, kg for kilogram and lb for

pound. In physics the quantities such as force and energy are usually measured

either In meters, kilograms, and seconds or in centimeters, grams and seconds, the

former being called the MKS system of units and the latter the CGS system of

unite). Both of these metric systems are referred to in scientific papers.

Загрузка...

Выбрать следующее задание

Ты добавил

Выбрать следующее задание

Ты добавил