Ancient philosophers tried to understand the essence of movement, to reveal the effect of stars and the sun on man. In addition, people have always tried to identify those forces that act on the material point in the process of its movement, as well as at the time of rest.
Aristotle believed that in the absence of movement, no forces exert an effect on the body. Let's try to find out which reference systems are called inertial, we give their examples.
Dormancy
In everyday life, it is difficult to identify such a condition. In almost all types of mechanical movement, the presence of extraneous forces is assumed. The reason is the force of friction, which prevents many objects from leaving their original position, leaving the state of rest.
Considering examples of inertial reference frames, we note that they all correspond to Newton’s law 1. Only after its discovery was it possible to explain the state of rest, to indicate the forces acting in this state on the body.
Newton's Law 1
In the modern interpretation, he explains the existence of coordinate systems with respect to which one can consider the absence of external forces acting on the material point. From Newton's point of view, reference frames are called inertial, which allow one to consider the preservation of the speed of the body for a long time.
Definitions
What reference systems are inertial? Examples of them are studied in the school physics course. Inertial consider such reference systems, relative to which the material point moves with constant speed. Newton specified that any body can be in a similar state as long as there is no need to apply forces to it that can change this state.
In reality, the law of inertia is not satisfied in all cases. Analyzing examples of inertial and non-inertial reference systems, we consider a person holding onto handrails in a moving vehicle. With sudden braking of the machine, a person automatically moves relative to transport, despite the absence of external force.
It turns out that not all examples of the inertial reference frame correspond to formulation 1 of Newton's law. To clarify the law of inertia, a refined definition of reference frames was introduced, in which it impeccably fulfills.
Types of reference systems
What reference systems are called inertial? It will become clear soon. “Give examples of inertial reference frames in which 1 Newton’s law is fulfilled” - a similar task is offered to schoolchildren who choose physics as an exam in the ninth grade. In order to cope with the task, it is necessary to have an idea of inertial and non-inertial reference systems.
Inertia involves maintaining rest or uniform rectilinear movement of the body as long as the body is in isolation. “Isolated” is considered to be bodies that are not connected, do not interact, are removed from each other.
Consider some examples of an inertial reference frame. If we consider the star in the Galaxy as a reference, rather than a moving bus, the fulfillment of the law of inertia for passengers who hold onto the handrails will be impeccable.
During braking, this vehicle will continue to move in a uniform rectilinear motion until other bodies act on it.
What examples of inertial reference system can be given? They should not have a connection with the analyzed body, affect its inertness.
It is for such systems that 1 Newton's law holds. In real life, it is difficult to consider the movement of the body relative to inertial reference systems. It is impossible to get to a distant star in order to conduct earth experiments with it.
The Earth is taken as a conditional reference frame, despite the fact that it is connected with objects placed on it.
The acceleration in the inertial reference frame can be calculated if the Earth's surface is considered as the reference frame. In physics, there is no mathematical notation 1 of Newton's law, but it is he who is the basis for deriving many physical definitions and terms.
Examples of inertial reference systems
It is sometimes difficult for students to understand physical phenomena. Ninth graders are offered the following task: “What reference systems are called inertial? Give examples of such systems. " Suppose that a trolley with a ball initially moves on a flat surface at a constant speed. Then it moves along the sand, as a result, the ball is brought into accelerated motion, despite the fact that other forces do not act on it (their total effect is zero).
The essence of what is happening can be explained by the fact that during movement along a sandy surface, the system ceases to be inertial, it has a constant speed. Examples of inertial and non-inertial reference systems indicate that their transition occurs in a certain period of time.
When the body accelerates, its acceleration has a positive value, and when braking, this indicator becomes negative.
Curved motion
Regarding the stars and the Sun, the Earth moves along a curved path, which has the shape of an ellipse. That reference system in which the center is aligned with the Sun, and the axes are directed at certain stars, will be considered inertial.
Note that any reference system that will move rectilinearly and uniformly relative to the heliocentric system is inertial. Curvilinear movement is carried out with some acceleration.
Given the fact that the Earth is moving around its axis, the reference system, which is connected with its surface, relatively heliocentric moves with some acceleration. In a similar situation, we can conclude that the frame of reference, which is connected with the Earth’s surface, moves with acceleration relative to the heliocentric, therefore it cannot be considered inertial. But the value of the acceleration of such a system is so small that in many cases it significantly affects the specifics of the mechanical phenomena considered with respect to it.
In order to solve practical problems of a technical nature, it is customary to consider inertial the reference frame that is rigidly connected to the Earth’s surface.
Galileo's Relativity
All inertial reference systems have an important property, which is described by the principle of relativity. Its essence lies in the fact that any mechanical phenomenon under the same initial conditions is carried out equally regardless of the chosen reference frame.
Equality of ISO on the principle of relativity is expressed in the following provisions:
- In such systems, the laws of mechanics are the same, so any equation that is described by them, expressed in terms of coordinates and time, remains unchanged.
- The results of mechanical experiments allow us to establish whether the reference system is at rest, or if it makes a rectilinear uniform motion. Any system can conditionally be recognized as motionless if the other at the same time makes relative motion to it at a certain speed.
- The equations of mechanics remain unchanged with respect to coordinate transformations in the case of a transition from one system to the second. One and the same phenomenon can be described in various systems, but their physical nature will not change.
Problem solving
The first example.
Determine if the inertial reference system is: a) an artificial Earth satellite; b) a children's attraction.
Answer. In the first case, there is no talk of an inertial reference system, since the satellite moves in orbit under the influence of gravity, therefore, the movement occurs with some acceleration.
The attraction also cannot be considered an inertial system, since its rotational movement occurs with some acceleration.
Second example.
The reporting system is firmly connected to the elevator. In what situations can it be called inertial? If the elevator: a) falls down; b) moves evenly up; c) rises rapidly; g) evenly goes down.
Answer. a) In a free fall, acceleration appears, therefore, the frame of reference that is associated with the elevator will not be inertial.
b) When the elevator moves uniformly, the system is inertial.
c) When moving with some acceleration, the reference system is considered inertial.
d) The elevator moves slowly, has a negative acceleration, so the reference frame cannot be called inertial.
Conclusion
Throughout its entire existence, mankind has been trying to understand the phenomena occurring in nature. Attempts to explain the relativity of the movement were made by Galileo Galilei. Isaac Newton was able to derive the law of inertia, which began to be used as the main postulate in calculations in mechanics.
Currently, the body positioning system includes a body, a time meter, and a coordinate system. Depending on whether the body is movable or motionless, it is possible to characterize the position of a certain object in the desired period of time.