When a teacher conducts a physics lesson at school, he often gives the following task to students: "Give examples of the manifestation of gravity." In this article, we will consider what the phenomenon of universal gravity is, and also show by examples the result of its manifestation.
Isaac Newton and his law
Each student is familiar with Newton’s three laws, which are used to describe the mechanical interaction between bodies and to study their movement. In this article, we will talk about the law of gravity, which was also discovered by Isaac Newton at the end of the XVII century. You should not think that the great Englishman was able to independently solve the problem of universal proportions. In fact, many of his predecessors guessed about mathematical dependence to determine the strength of the interaction between massive bodies. Newton’s merit is the systematization and detailed analysis of accumulated scientific experience, which led to the emergence of the law of universal gravitation. The corresponding formula is as follows:
F = G * m 1 * m 2 / r 2 .
Its verbal description is as follows: the force F of attraction between bodies with masses m 1 and m 2 is directly proportional to the product of their masses and inversely proportional to the distance r between them. The value of G is the gravitational constant.
When considering the phenomenon of gravity and the force of gravity, it should be remembered that it acts between absolutely any bodies in the Universe that have finite mass.
Force of gravity
If a high school student hears the words "Earth's gravity", then the following formula pops up in his memory:
F = m * g,
where g is the acceleration of gravity. However, few know where this formula comes from. It is obtained directly from the above expression for the force F. Indeed, in the case of our planet, we should consider a body of mass m and Earth of mass M. The distance between them is approximately equal to the radius of the Earth R, then:
F = G * m * M / R 2 = m * g, where g = G * M / R 2 .
If we substitute the mass and radius of the planet into the equality for g, then we get g = 9.81 m / s 2 .
The value of g is not a constant on Earth. In a given area, it depends on the features of the relief and the presence of minerals and voids in the earth's crust. Nevertheless, these changes make up a fraction of a percent. With increasing height, g decreases, but even at an altitude of 300-400 km it changes by only 5%.
Examples of gravity
When they ask: "Give examples of the manifestation of gravity of force in earthly conditions and in everyday life," then the first thing to be called is the fall of any bodies down. Regardless of whether the body is thrown up, whether it is heavy or light, or released at a certain height, it always falls to the ground. Trajectories of incidence can be parabolic or rectilinear, which depends on the direction of the initial velocity of the body.
Another class of examples of the action of gravity on Earth is the appearance of weight on all bodies that are on a support or suspended on a thread, spring, and so on. For example, a glass of water on a table experiences the action of gravity with which it presses on the surface of the table. The latter responds by generating an upward force that balances the force of gravity.
Examples of gravity in space
If the teacher asks: “Give examples of the manifestation of gravity of force in outer space,” the first thing to do is call the rotation of our and other planets around the Sun. The force of gravity between the star and its planets plays the role of a centripetal force, which causes our Earth, Venus, Mars and other bodies to rotate in some closed orbits.
The force of attraction also manifests itself in the fact that many planets have satellites, that galaxies exist as single clusters and do not scatter into individual stars.
Performing the task with the wording "give examples of the manifestation of the force of gravity," we should also mention the deviation from the rectilinear trajectory of electromagnetic waves when they propagate near massive space objects.