Physics | Introduction to matter units and the three laws of Newtonian mechanics
Introduction to matter units
The definition of matter is limited by the definition of the universe, and the instantaneous state of the universe is given after ignoring the time increment. The order of material units from largest to smallest is matter, molecules, atoms , nuclei and electrons, protons and neutrons , quarks .
molecular atom negative ion positive ion proton = neutron electron; the molecule is composed of two or more atoms; the atom contains the nucleus, and there are protons and neutrons in the nucleus. The proton has a positive potential and the neutron is uncharged. The neutron and the proton are the same size. The number of neutrons and protons is equal or slightly different. There are particles outside the nucleus that electrons move in irregular circles around the nucleus. They have a negative potential and their number is equal to the number of protons.
1. Ion: When an atom gains or loses electrons, it is called an ion. The atom that gains electrons is called a negative ion, and the one that loses electrons is a positive ion.
2, quantum : In the microscopic field, changes in certain physical quantities occur in leaps and bounds in the smallest unit, rather than continuously. This smallest unit is called quantum, which is also the collective name for the basic units of matter such as atoms, electrons, photons .
3, molecules, atoms, protons, neutrons, electrons, quanta, and ions are all particles.
The smallest unit of matter is the quark.
Quark is a basic particle that participates in strong interactions and is also the basic unit of matter. Quarks combine with each other to form a composite particle called hadron . The most stable hadrons are protons and neutrons, which are the building blocks of atomic nuclei.
Quark is a basic particle that participates in strong interactions and is also the basic unit of matter. In addition, there are six known types of quarks. The types of quarks are called "flavors", they are up (u), down (d), odd (s), beam (c), bottom (b) and top (t). Up and down quarks have the lowest masses of all quarks. Heavier quarks quickly become up or down quarks through a process called particle decay.
All interactions that occur in nature, all matter and energy, can be explained by the splitting and combining of strings. Inside each elementary particle, there is a thin line vibrating, just like the vibration of a violin string.
The properties of different particles are determined by the different vibration behaviors of strings. Electrons are strings that vibrate in a certain way, and quarks on are strings that vibrate in another way. There are three kinds of quarks in the proton, two top quarks and one bottom quark. They form a stable triangular structure, which is a strongly interacting energy structure relationship. The existence of the three restricts each other.
Newton's three laws of mechanics
Newton's three laws of mechanics are: the law of inertia, the law of acceleration and the law of action and reaction. Newton's law of motion is only established in the inertial reference system, also known as Newton's reference system.
1. Newton's first law of
Content: All objects always remain at rest or in a state of uniform linear motion when there is no force or the resultant force is zero.
Description: Objects have the tendency to remain stationary and move in a straight line at a uniform speed. Therefore, the motion state of an object is determined by its motion speed . Without external force, its motion state will not change. This property of an object is called inertia. So Newton's first law is also called the law of inertia. The first law also explains the concept of force. It is clear that force is the interaction between objects, and it is pointed out that force changes the motion state of objects. Because acceleration describes changes in the motion state of an object, force is related to acceleration, not to speed. If you don’t pay attention to this in daily life, it is often easy to create misunderstandings.
Note: Newton's first law does not hold true in all reference frames. In fact, it only holds true in the inertial reference frame .Therefore, whether Newton's first law is true is often used as a criterion for whether an reference system is an inertial reference system.
2. Newton's second law
content: An object will generate acceleration when acted upon by a net external force. The direction of the acceleration is the same as the direction of the net external force. The magnitude of the acceleration is directly proportional to the magnitude of the net external force and inversely proportional to the inertial mass of the object.
Formula: F=ma, F is the total external force
Newton's second law quantitatively describes the effect of force and quantitatively measures the inertia of an object. It is vector and instantaneous.
should emphasize that when an object is subjected to a non-zero external force, it will generate acceleration, causing the object's motion state or speed to change, but this change is related to the motion state of the object itself.
Limitations: This law only applies to low-speed motion of macroscopic objects.
3. Newton's third law
Content: The action force and reaction force between two objects are equal in magnitude and opposite in direction on the same straight line.
needs to pay attention to:
(1) Action force and reaction force have no priority or order. Create and disappear at the same time.
(2) This pair of forces acts on different objects and cannot be offset.
(3) The action force and reaction force must be of the same nature.
(4) has nothing to do with the frame of reference. The first law of
introduces the concept of force and clarifies the properties of inertia, qualitatively reveals the relationship between force and motion, lays the foundation and prepares the necessary concepts for the second law of ; the third law further gives the nature of the force and reveals the mutual restriction mechanism of object movement. The combination of the three laws comprehensively solves the problem of motion of any object after being acted upon by complex external forces.
Newton's law of motion is an organic whole, a complete theoretical system of the same origin, and the basic axioms of mechanics. The momentum theorem, law of conservation of momentum , kinetic energy theorem , law of conservation of mechanical energy , moment of momentum theorem, and law of conservation of angular momentum derived from them further confirm the compatibility and consistency of the dynamic axiomatic system.
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