Weight formula

In everyday life and everyday life the concepts of "mass" and "weight" are absolutely identical, although their semantic value is fundamentally different. Asking "What's your weight?" We mean "how many kilos are there in you?". However, the question with which we are trying to clarify this fact, the answer is given not in kilograms, but in newtons. I'll have to return to the school course of physics.

Body weight is a measure of the strength with which the body exerts pressure on the support or suspension.

For comparison, the body weight was earlier roughly defined as the "amount of substance", the modern definition sounds like this:

Mass is a physical quantity reflecting the body's ability to inertia and is a measure of its gravitational properties.

The concept of mass in general is somewhat wider than that presented here, but our task is somewhat different. It is quite enough to understand the fact of the actual difference between mass and weight.

In addition, the unit of measurement of mass is kilograms, and weights (as a kind of force) are newtons.

And, perhaps, the most important difference between weight and mass is the weight formula itself, which looks like this:

P = mg

Where P is the actual body weight (in Newtons), m is its mass in kilograms, and g is the acceleration of gravity, which is usually expressed as 9.8 N / kg.

In other words, the weight formula can be understood in this 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, are at rest, you can safely 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 acting weight on the suspension dynamometer. Hence 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 observation. The weight formula is equal to the force of the gravity formula only in cases when:

• The body is in a state of rest;
• On the body does not act Archimedes force (buoyant force). A curious fact concerning the buoyancy force: 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 "lighter" for the volume of displaced water. That's why you can lift a girl in the water with a mass of 60 kg, joking and laughing, and on the surface this is much more difficult.

With uneven movement of the body, i.e. When the body together with the suspension moves with the acceleration a , it changes its shape and weight formula. The physics of the phenomenon varies insignificantly, but in the formula such changes find the following reflection:

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 should be greater than the acceleration of gravity. And here again it is important to distinguish between weight and mass: the negative weight does not affect the mass (the properties of the body remain the same), but it actually becomes directed in the opposite direction.

An example with an accelerated elevator is good: when it is accelerated for a short time, it seems like "pulling to the ceiling." Of course, such a sensation is quite easy to encounter. It is much more difficult to feel the state of weightlessness, which is fully felt by the astronauts in orbit.

Weightlessness is essentially a lack of weight. In order for this to be possible, the acceleration with which the body moves should be equal to the notorious squalor g (9.8 N / kg). To achieve such an effect is easiest in a near-earth orbit. Gravity, i.e. Attraction, still acts on the body (satellite), but it is negligible. And the acceleration of the satellite drifting along the orbit also tends to zero. This is where the effect of lack of weight occurs, because the body does not touch either the support or the suspension, but simply floats in the air.

Partly with this effect can be encountered during takeoff of the aircraft. For a second there is a feeling of suspension in the air: at this moment the acceleration with which the plane moves is equal to the acceleration of free fall.

Returning again to differences in weight and mass, it is important to remember that the formula for body weight is different from the mass formula, which looks like :

M = ρ / V,

That is, the density of matter divided by its volume.