In order to make it convenient to work with different quantities in physics, their standard notation is used. Thanks to them, everyone can easily remember many important formulas for certain processes. In this article, we consider the question of what g means in physics.
The phenomenon of gravity
To understand what g means in physics (in the 7th grade of secondary schools this topic is covered), one should get acquainted with the phenomenon of gravity. At the end of the 17th century, Isaac Newton published his famous scientific work, in which he formulated the basic principles of mechanics. In this work, he allocated a special place for the so-called law of universal gravitation. According to it, all bodies that have a finite mass are attracted to each other regardless of the distance between them. The force of attraction between bodies with masses m 1 , m 2 is calculated by the following formula:
F = G * m 1 * m 2 / r 2 .
Here G is the universal gravitational constant, r is the distance between the centers of mass of bodies in space. The force F is called the gravitational interaction, which, like the Coulomb interaction, decreases with the square of the distance, but unlike Coulomb gravity is only attractive.
Acceleration of gravity
The title of this section of the article is the answer to the question of what the letter g means in physics. They use it because from the Latin language the word "gravity" will be gravitas. Now it remains to understand what free fall acceleration is. To do this, consider what force acts on every body located near the surface of the Earth. Let the body have mass m, then we get:
F = G * m * M / R 2 = m * g, where g = G * M / R 2 .
Here M, R is the mass and radius of our planet. Note that even if the body is at a certain height h above the surface, then this height is much less than the value of R, therefore, it can be ignored in the formula. We calculate the value of g:
g = G * M / R 2 = 6.67 * 10 -11 * 5.972 * 10 24 / (6371000) 2 = 9.81 m / s 2 .
What does g mean in physics? The acceleration g is such a value by which the speed of absolutely any body that falls freely on the surface of the Earth increases. From the calculations it follows that the increase in speed for each second of fall is 9.81 m / s (35.3 km / h).
Note that the value of g does not depend on body weight. In fact, you can see that more dense bodies fall faster than less dense. This happens because different air resistance forces act on them, and not different gravity.
The formula above allows you to determine g not only for our Earth, but also for any other planet. For example, if we substitute the mass and radius of Mars into it, then we get a value of 3.7 m / s 2 , which is almost 2.7 times less than for Earth.
Body weight and acceleration g
We examined above what g means in physics, it also turned out that this is the acceleration with which all bodies fall in air, and also g is a coefficient in calculating gravity.
Now consider the situation when the body is at rest, for example, a glass is on the table. Two forces act on it - gravity and support reactions. The first is related to gravity and directed downward, the second is due to the elasticity of the table material and directed upward. The glass does not fly up and does not fall through the table only because both forces balance each other. In this case, the force with which the body (glass) presses on the support (table) is called the weight of the body. Obviously, the expression for it will take the form:
P = m * g.
Body weight is not constant. The formula written above is valid for a state of rest or uniform movement. If the body moves with acceleration, then its weight can both increase and decrease. For example, the weight of astronauts, whose launch vehicle enters near-Earth orbit, increases several times during launch.