In everyday life and everyday life, the concepts of "mass" and "weight" are absolutely identical, although their semantic meaning is fundamentally different. Asking "What is your weight?" we mean "How many kilograms do you have?". However, the question with which we are trying to find out this fact is answered not in kilograms, but in newtons. Have to go back to school physics course.
Body weight - a value that characterizes the force with which the body exerts pressure on a support or suspension.
For comparison, body weight was previously roughly defined as the "amount of substance", the modern definition sounds like this:
Mass is a physical quantity that reflects the body's ability to inertia and is a measure of its gravitational properties.
The concept of mass is generally somewhat wider than presented here, however, our task is somewhat different. It is sufficient to clarify the fact of the actual difference between mass and weight.
In addition, the unit of measurement of mass is kilograms, and weight (as a type of force) is Newtons.
And, perhaps, the most important difference between weight and mass is the weight formula itself, which is as follows:
P = mg
where P is the actual body weight (in Newtons), m is its mass in kilograms, and g is the gravitational acceleration , which is usually expressed as 9.8 N / kg.
In other words, the weight formula can be understood with the following example:
A weight of 1 kg is suspended from a stationary dynamometer in order to determine its weight. Since the body, and the dynamometer itself, is at rest, it is safe to multiply its mass by the acceleration of gravity. We have: 1 (kg) x 9.8 (N / kg) = 9.8 N. It is with such force that the weight acts on the suspension of the dynamometer. From this it is clear that body weight is equal to gravity. However, this is not always the case.
It's time to make an important point. The weight formula is equal to the strength of the gravity formula only in cases when:
- the body is at rest;
- the force of Archimedes (buoyant force) does not act on the body. An interesting fact about buoyancy: it is known that a body immersed in water displaces a volume of water equal to its weight. But it does not just push water, the body becomes βlighterβ by the volume of water displaced. Thatβs why you can raise a girl weighing 60 kg in water by joking and laughing, but on the surface it is much more difficult to do.
With uneven body movement, i.e. when the body, together with the suspension, moves with acceleration a , it changes its appearance and weight formula. The physics of the phenomenon varies slightly, but in the formula such changes are reflected in the following:
P = m (ga).
As can be replaced by the formula, the weight can be negative, but for this the acceleration with which the body moves must be greater than the acceleration of gravity. And here again, it is important to distinguish weight from mass: negative weight does not affect mass (body properties remain the same), however, it actually becomes directed in the opposite direction.
A good example with an accelerated elevator: when it is sharply accelerated for a short time, the impression of "pulling to the ceiling" is created. Of course, it is quite simple to encounter such a feeling. It is much more difficult to feel the state of weightlessness, which is fully felt by the astronauts in orbit.
Weightlessness - in fact, lack of weight. In order for this to be possible, the acceleration with which the body moves must be equal to the notorious litter g (9.8 N / kg). It is easiest to achieve this effect in near-Earth orbit. Gravity i.e. attraction, still acts on the body (satellite), however it is negligible. And the acceleration of a satellite drifting in orbit also tends to zero. This is where the effect of lack of weight arises, since the body generally does not come into contact with either the support or the suspension, but simply soars in the air.
Partly this effect can be encountered when taking off the plane. For a second there is a feeling of being suspended in the air: at this moment, the acceleration with which the plane moves is equal to the acceleration of gravity.
Returning again to the differences in weight and mass, it is important to remember that the body weight formula is different from the mass formula, which looks like :
m = Ο / V,
that is, the density of a substance divided by its volume.