Gravity is a natural phenomenon that is present anywhere on our planet. The force with which the Earth's gravitational field acts on an object with a finite mass is called gravity. Consider how gravity is measured.
The law of gravity, or when people learned about the existence of gravity
At first glance this question sounds naive. Indeed, the very first ancestor of man walked the earth and already felt that it attracted him and all surrounding objects. Nevertheless, a scientific study of this issue began not so long ago.
At the beginning of the XVII century, Galileo first measured the gravitational field of our planet, dropping bodies of different masses from the famous tower in Pisa. The Italian scientist also owns the invention of the mathematical pendulum, which can be used to determine the acceleration of gravity g.
In the second half of the same XVII century, Isaac Newton, studying the laws of planetary motion, which were empirically obtained by Johannes Kepler, theoretically derived the law of universal gravitation. Its mathematical formulation is presented below:
F = G * m 1 * m 2 / r 2 .
Here, the interaction force F between bodies with masses m 1 and m 2 occurs when they are at a distance r from each other. The value of G is a constant that remains unchanged for any point in our universe, it is equal to 6.674 * 10 −11 N * m 2 / kg 2 . This value indicates that two bodies with masses of 1 kilogram each, the distance between which is 1 meter, are attracted with a force of ≈ 0.06674 nanonewton. The order of this magnitude explains why in life we do not feel attraction from other bodies.
Body weight
Before answering the question of what gravity is measured in, we will get acquainted with body weight. This value directly follows from the law of gravitation formulated above. If we substitute the mass of the Earth and its radius (the distance between the center of gravity of the planet and objects located near its surface is approximately equal to the radius of the Earth) in the formula for the gravity that every object on our planet experiences, then we get the expression:
F = G * M / R 2 * m = g * m = P, where g = G * M / R 2 .
Thus, we have obtained a formula for the gravitational force of bodies by the Earth. This force is called weight. Weight depends only on one’s own body weight. When the gravitational field changes, the weight also changes. This situation is observed if you climb high into the mountains or fly to another planet.
In what units is gravity measured?
Since this is a force, it is measured in Newtons (N). However, in the generally accepted SI system, Newton is not a basic unit, but is introduced into physics due to other quantities: mass, distance, and time. A force of 1 Newton means that it can accelerate a body weighing 1 kilogram in 1 second to a speed of 1 meter per second. This conclusion follows from the second law of Isaac Newton in classical mechanics.
Work of gravitational forces
Having considered the question of how gravity is measured in physics, we can proceed to the concept of work. In the general case, this quantity is understood as the scalar product of the force acting on the body and the vector of its displacement in space, which can be written as an expression:
A = (F¯ * l¯).
Parentheses indicate that this product is a scalar (work is an e vector value). Opening these brackets and passing to the modules of quantities, we obtain:
A = l * F * cos (α).
Where α is the angle between the corresponding vectors. The formula obtained allows us to make an important conclusion: the force F will not do work if it acts perpendicular to the direction of movement l of the body (cos (90) = 0).
How is gravity measured? Like any other work in physics, it is measured in joules. Gravity (body weight) is directed strictly toward the center of the earth. In practice, this direction coincides with the vertical. This means that gravity will only do work when the body is lifted up or lowered. This fact allows us to write down the formula for the work of this force:
A = m * g * h.
Where h is the change in body height during its movement.
Examples of the manifestation of the work of gravity in everyday life
Perhaps the most striking is the person climbing the stairs. Since the weight of the body is directed downward, during the ascent along the steps it is directed against the movement of the human body, that is, it performs negative work. This work will be the greater, the higher the lifting height and the greater the mass of the body (it is very difficult for full people to climb the upper floors of the building on foot). On the contrary, when descending, gravity is directed along the direction of movement, so it does a positive job and independently lowers the body down (moving down a ladder or hillside).
It is curious to note that if a person took a load and carries it, then gravity does not interfere and does not contribute to such movement (A = 0). Movement with a heavy load is difficult, because the force of rest friction increases (it is directly proportional to body weight), which a person is forced to overcome in order to take at least one step.
What instrument measures gravity?
This is what it is called - a gravimeter, that is, measuring gravity. The very first gravimeter is considered to be the Galilean pendulum. In honor of the name of this scientist, the unit of measurement with which the gravimeter works is called Gal. The value of 1 Gal corresponds to 0.01 m / s 2 . Note that the answer to the question of what is measured by gravity is a newton, but the gravimeter does not measure newtons, but the acceleration that gravity gives to bodies.
The gravimeter is widely used in geology in the analysis of the structure of the earth's interior and the search for minerals (ore deposits cause local fluctuations in g).
All gravimeters are divided into two classes:
- Absolute - measure directly the gravitational field, that is, g. Until the middle of the last century, pendulums were used for this purpose, now they are using devices in which the time of falling of a body in a vacuum is directly studied.
- Relative. They measure the fluctuations of the gravitational field at different points on the earth. In order to determine the value of g in a given area using such a gravimeter, it is necessary to know its exact value for this device in some other area. Often used spring gravimeters. In the early 2000s, a superconducting relative gravimeter was constructed. Its principle of operation is based on a change in the position of a superconducting diamagnetic sphere suspended from a magnetic field from niobium cooled by liquid helium. The sensitivity of this gravimeter is so great (≈ 1 nGal) that it captures changes in gravity caused by a change in the thickness of the snow cover on the Earth’s surface literally a few centimeters.