Body weight is the force with which it presses on a support or a suspension under the influence of a gravitational attraction. At rest body weight is equal to gravity and gm is calculated on formula P =. In life often use the wrong definition of the concept "weight", including its similar to the concept "weight". For example, speaking about the person: "he weighs 80 kilograms". Actually, the weight of this person would be about 9.81*80 = 784.8 N (newtons).
Instruction
1. It is known that the third law of Newton says: "Force of action is equal to counteraction force". That is that force with which the body affects a support or a suspension has to be equal in your case to force of reaction of this support or suspension. Let's assume, any body the mass of m is on a motionless support. In this case, force of reaction of support N is in number equal to the body gravity (its weight). Therefore, weight is equal to GM.
2. And if the support should is mobile? There is a characteristic example: the person came into the elevator, pressed the button of the above-located floor. The elevator went up, and at once it seemed to the person as if his body became heavier. Why does that happen? In a cabin of the elevator there is a body the mass of m. It began to move with acceleration of an up. At the same time force of reaction of a support (elevator cab floor) is equal to N. What is body weight equal to?
3. According to the second law of Newton, any force operating on a body can be presented how the work of sizes of mass of this body and acceleration with which it moves. At the movement vertically up taking into account that vectors of accelerations of g and an are sent to the opposite directions, it turns out: mg + N = ma, or mg + ma = N. From this it follows that N = m(g+a). And as weight P is in number equal to reaction of support N, in this case: P = m(g+a).
4. From the above-stated formula it is easy to understand why at the movement in the elevator it seems to the person up as if it became heavier. Certainly, the more there will be an acceleration of a, the more there will be also a body weight of R.A if the elevator moves not up, and down? Arguing in precisely the same way, you receive a formula: N = m (g – a), that is, weight P = m(g-a). It is easy to understand why at the movement it seems to the person down as if he became easier. And the more acceleration of a, the less will be body weight.
5. And what will occur if acceleration of a practically is leveled with the acceleration of gravity of g? Then will arise weightlessness state, well familiar to astronauts. Then P body weight = m(g-g) = 0.