In everyday life and everyday life the concept of "mass" and "weight" are identical, although the semantic value of their fundamentally different.Asking "What is your weight?"we mean "How many kilograms you?".However, the question with which we are trying to figure out this fact, the answer is not given in kilograms, and newtons.We'll have to go back to school physics course.
Body weight - value characterizing the force with which the body exerts pressure on the support or suspension.
For comparison, weight previously roughly defined as "amount of substance", the modern definition is thus:
Weight - physical quantity that reflects the ability of the body to the inertia is a measure of its gravitational properties.
concept of mass in general somewhat broader presented here, but our task is somewhat different.It is enough to understand the difference between the actual fact of mass and weight.
In addition, the unit of measurement of weight - weight, and weight (as type of force) - Newton.
And perhaps the most important difference between the weight of the mass contains the formula of weight, which is as follows:
P = mg
where P - is the actual body weight (in Newtons), m - its massin kilograms, and the g - acceleration of free fall, which is usually expressed in the form of 9.8 N / kg.
other words, the formula weight can be understood by the following example:
Kettlebell 1 kg weight is suspended on a fixed dynamometer in order to determine its weight. Because the body, and indeed the dynamometer are at rest, it is to be its mass multiplied by the acceleration of free fall.We have: 1 (kg) x 9.8 (H / kg) = 9.8 N. It was with such force acts on the weight suspension dynamometer.It is clear that the weight of the body is equal to the force of gravity.However, this is not always the case.
It's time to make an important point.Formula weight is equal to the force of gravity formula only in the cases when:
- body is in a state of rest;
- on the body is not the force of Archimedes (buoyancy).A curious fact about the buoyancy force: it is known that a body immersed in water displaces a volume of water equal to its weight.But it is not just pushing the water, the body becomes "easier" on the volume of water displaced.That is why the raise in water Woman weighing 60 kg can be joking and laughing, but on the surface it is much harder to do.
When non-uniform motion of the body, ie,when the body together with the suspension moving with acceleration a , changes its appearance and the formula weight.Physics phenomenon varies slightly, but these changes in the formula are the following reflection:
P = m (ga).
How can replace the formula, the weight can be negative, but this acceleration with which a body is moving, must be greater than the gravitational acceleration.Here again it is important to distinguish the weight by weight: weight no negative effect on the weight (body properties are the same), but it actually becomes directed in the opposite direction.
good example with the accelerated lift: with its sharp acceleration for a short time the impression "pull to the ceiling."With such a feeling, of course, encounter quite simple.It is much harder to experience the state of weightlessness, which fully feel the astronauts in orbit.
Weightlessness - essentially no weight.To this was possible, the acceleration with which the body moves, should be equal to the notorious usoreniyu g (9,8 N / kg).To achieve this effect is easiest in low Earth orbit.Gravity, ieattraction still acts on the body (satellite), but it is negligible.But the acceleration of drifting in orbit satellites also tends to zero.And then there is the effect of the lack of weight, because the body does not come into contact with any support, either with the suspension, but simply hovers in the air.
Partly this effect may be encountered during takeoff.For a moment, the feeling being suspended in the air at this point acceleration, which moves the plane, equal to the acceleration of free fall.
Returning again to the differences weight and mass important to remember that the formula weight of the body is different from the formula weight that looks like :
m = ρ / V,
that is, the density of matterdivided by its volume.
