1687, Newton put forward the famous three laws of Newton's motion in Mathematical Principles of Natural Philosophy. Newton's three laws are the cornerstone of Newton's mechanics building, and the second law can be explained by a very simple mathematical expression:
Newton's second law tells us:
1. Force can cause an object to accelerate. The greater the mass of the same force, the greater the inertia and the smaller the acceleration. On the contrary, the smaller the mass, the smaller the inertia and the greater the acceleration, which explains the quantitative relationship between force and object motion.
We can know the mass of an object by measuring force and acceleration. Theoretically, if we want to know the mass of an object, we must break it down into the most basic components and add them up one by one, just like spelling Lego, so as to know the mass of the object.
With Newton's second law, it is not so complicated. As long as the acceleration and output are measured, the mass can be known.
3. The scale we usually use can measure a kind of mass, which is called gravitational mass, that is, are these two masses the same?
Most of us have not thought about this problem carefully, and naturally feel that these two kinds of people are equal. One is when we push an object hard, but the object tries to keep its original state, that is, inertia, the mass we feel, and the other is the mass we measure by comparing the gravitational mass of the reference object (that is, the counterweight) under the action of the gravity of the earth.
These two qualities seem quite different.
Indeed, before Einstein 19 15 founded the general theory of relativity, everyone thought that these two masses, one is different from the other, slightly different.
However, Einstein thought that the two can be considered equal, that is. So you can see what you see in science fiction movies. Humans have built bases suitable for human habitation in outer space. This base is always rotating, and circular motion will produce acceleration. When this acceleration is equal to the acceleration of gravity, we won't feel weightless.
It feels like the earth. It's hard to tell. In this way, although gravitational mass and inertial mass are different in nature, they can be treated uniformly in general relativity, which is the so-called "equivalence principle" and one of the prerequisites for Einstein to establish general relativity.