Mass is a physical quantity that characterizes the inertia of a body. Mass The greater the mass of a body, the more inert it is.
Exploring the difference between weight and body weight Newton did. He reasoned as follows: we know perfectly well that different substances, taken in the same volumes, weigh unequally.
Weight
The amount of matter contained in an object, Newton called the mass.
Weight- something common that is inherent in all objects without exception - it does not matter whether they are shards from an old clay pot or a gold watch.
For example, a piece of gold is more than twice as heavy as the exact same piece of copper. It is likely that particles of gold, Newton suggested, are able to fit more densely than particles of copper, and more substance can fit in gold than in a piece of copper of the same size.
Modern scientists have found that the different density of substances is explained not only by the fact that the particles of the substance are stacked more densely. The smallest particles themselves - atoms - differ in weight from each other: gold atoms are heavier than copper atoms.
Whether an object lies motionless, or freely falls to the ground, or sways, suspended by a thread - it mass under all conditions remains unchanged.
When we want to find out how big the mass of an object is, we weigh it on the usual commercial or laboratory scales with cups and weights. We put an object on one scale pan, and weights on the other, and thus compare the mass of the object with the mass of the weights. Therefore, trade and laboratory scales can be transported anywhere: to the pole and to the equator, to the top high mountain and deep mine. Everywhere and everywhere, even on other planets, these scales will show correctly, because with their help we determine not weight, but mass.
IN different points land can be measured with a spring balance. By attaching an object to the hook of a spring balance, we compare the force of gravity of the Earth experienced by this object with the force of elasticity of the spring. The force of gravity pulls down, (in more detail:) the force of the spring - up, and when both forces are balanced, the scale indicator stops at a certain division.
Spring balances are correct only at the latitude where they are made. At all other latitudes, at the pole and at the equator, they will show different weights. True, the difference is not great, but it will still be revealed, because the force of gravity on Earth is not the same everywhere, and the elastic force of the spring, of course, remains constant.
On other planets, this difference will be significant and noticeable. On the Moon, for example, an object that weighed 1 kilogram on Earth will pull 161 grams on spring scales brought from Earth, on Mars - 380 grams, and on huge Jupiter - 2640 grams.
The greater the mass of the planet, the greater the force with which it attracts a body suspended on a spring balance..
Therefore, the body weighs so much on Jupiter and so little on the Moon.
Convert the following values to kg: 20 g = 200 g = 250 mg = 28.3 mg = 75.6 g = 150 t = Mass units in the SI system: = 1 kg. Mass units: 1 t = 1000 kg; 1 g = 0.001 kg; 1 mg \u003d 0, kg 1 c \u003d 100 kg
Answers: 20 g = 0.02 kg 200 g = 0.2 kg 250 mg = 0.00025 kg 28.3 mg = 0 kg 75.6 g = 0.0756 kg 150 t = kg
In practice, body weight can be measured using scales. Scales happen various types: educational, medical, analytical, pharmaceutical, electronic, etc. Scales are lever and spring. Let's look at a few examples. Technical floor scales Scales for measuring surface tension forces Single-cup lever scales Small spring scales Medical scales Laboratory analytical balances
1. Before weighing, make sure that the balance is balanced. 2. The body to be weighed is placed on the left pan of the scales, and the weights on the right pan. 3. In order to avoid damage to the scales, lower the body and weights carefully. 4. Do not weigh bodies heavier than the maximum load indicated on the scales. 5. Do not put wet, dirty, hot bodies on the scales, pour powders, pour liquids. 6. Small weights should be taken only with tweezers. 7. After weighing, transfer the weights from the balance pan to the case and check that all the weights are in place.
From the point of view of classical mechanics, the mass of a body does not depend on its motion. If the mass of a body at rest is equal to m 0, then for a moving body this mass will remain exactly the same. The theory of relativity shows that in reality this is not the case. Body mass T, moving at speed v, expressed in terms of the rest mass as follows:
m \u003d m 0 / √ (1 - v 2 /c 2) (5)
We note right away that the speed appearing in formula (5) can be measured in any inertial frame. In different inertial systems, the body has different speed, in different inertial frames it will also have a different mass.
Mass is the same relative value as speed, time, distance. It is impossible to talk about the magnitude of the mass until the frame of reference in which we study the body is fixed.
It is clear from what has been said that, when describing a body, one cannot simply say that its mass is such and such. For example, the sentence "the mass of the ball is 10 g" is completely indefinite from the point of view of the theory of relativity. The numerical value of the mass of the ball still does not tell us anything until the inertial frame with respect to which this mass is measured is indicated. Usually, the mass of a body is given in an inertial frame associated with the body itself, i.e., the rest mass is given.
In table. 6 shows the dependence of body mass on its speed. It is assumed that the mass of the body at rest is 1 AU. Speeds less than 6000 km/s are not given in the table, since at such speeds the difference between mass and rest mass is negligible. At high speeds, this difference becomes already noticeable. The greater the speed of the body, the greater its mass. So, for example, when moving at a speed of 299 700 km/s body weight increases by almost 41 times. At high speeds even a slight increase in speed significantly increases body mass. This is especially noticeable in Fig. 41, which graphically depicts the dependence of mass on speed.
Rice. 41. The dependence of mass on speed (the rest mass of the body is 1 g)
In classical mechanics, only slow motions are studied, for which the mass of the body differs very little from the rest mass. When studying slow motions, the body mass can be considered equal to the rest mass. The mistake we make in doing so is almost imperceptible.
If the speed of the body approaches the speed of light, then the mass grows indefinitely, or, as they say, the mass of the body becomes infinite. Only in one single case can a body acquire a speed equal to the speed of light.
It can be seen from formula (5) that if the body moves at the speed of light, i.e. if v
= from and √(1 - v 2 /c 2), then it must be equal to zero and the value m0.
If this were not the case, then formula (5) would lose all meaning, since dividing a finite number by zero is an unacceptable operation. A finite number divided by zero equals infinity - a result that has no definite physical sense. However, we can make sense of the expression "zero divided by zero". Hence it follows that only objects with zero rest mass can move exactly at the speed of light. Such objects cannot be called bodies in the usual sense.
The equality of the rest mass to zero means that a body with such a mass cannot rest at all, but must always move at a speed c. An object with zero rest mass, then light, more precisely, photons (light quanta). Photons can never rest in any inertial frame, they always move with a speed from. Bodies with non-zero rest mass can be at rest or move at different speeds, but at lower speeds of light. They can never reach the speed of light.
In the very broad sense Body weight refers to the amount of matter contained in the body. Mass is measured in kilograms in the generally accepted international system SI units.
Body weight reference
The mass standard of 1 kilogram is made of an alloy, 90% platinum and 10% iridium. This standard is located at the International Bureau of Weights and Measures, not far from Paris. It has the shape of a cylinder, the height and diameter of which are 39.17 mm.
Often, body weight is called weight, which, strictly speaking, is completely incorrect. The confusion is caused by the fact that a body of mass 1 kg. has a weight of 1 kgf (kilogram-force). This is an off-system unit of measurement and it is equal to the force required to give a body a mass of 1 kg. acceleration equal to the acceleration g of free fall, approximately 9.81 m / (s ^ 2)
Different definitions of mass
IN different areas and fields of physics use different definitions of mass:
- based on Newton's II law, m = f / a, mass is the ratio of the force applied to the body and the acceleration reported by this force;
- based on the law of gravity, this is the ratio of the force of attraction to the acceleration of free fall, m = F / g, .
- in general physics and in the theories of relativity, the definition of mass is still used as the ratio of momentum P to velocity v, m = P / v.
Mass is a non-negative scalar quantity. The mass of a photon (a particle that can exist in vacuum only by moving at the speed of light) is considered to be zero.
There are many different units of mass measurement, many of them, like the ounce, carat, pound, barrel, have their own historical origin.
The mass of a body is a scalar physical quantity that characterizes its inertia. Inertia is the property of a body to change its state. The greater the body weight, the easier it is to change the state of the body.
Let's write down Newton's 2nd law: a = F/m, where a is the acceleration of the body under the action of the force F.
From the expression we see that the greater the body mass m, with the same operating force F, the less acceleration of body a. The greater the mass of the body, the less it changes its state.
Body weight is measured in kilograms.
1 kg is such a body mass at which, under the action of a force of F = 1 Newton on it, the body will acquire an acceleration of a = 1 m / s ^ 2.
