Ancient philosophers tried to understand the essence of movement, to reveal the influence of stars and the Sun on a person. In addition, people have always tried to identify the forces that act on a material point in the process of its movement, as well as at a moment of rest.
Aristotle believed that in the absence of movement, the body is not affected by any forces. Let's try to find out which frames of reference are called inertial, we will give examples of them.
Resting state
In everyday life it is difficult to detect 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 does not allow many objects to leave their original position, to leave the state of rest.
Considering examples of inertial reference systems, we note that they all correspond to Newton's 1st law. Only after its discovery was it possible to explain the state of rest, to indicate the forces acting in this state on the body.
Formulation of Newton's 1st law
In the modern interpretation, he explains the existence of coordinate systems, relative to which one can consider the absence of external forces acting on a material point. From Newton's point of view, reference systems are called inertial, which allow us to consider the conservation of the body's velocity over a long time.
Definitions
Which frames of reference are inertial? Examples of them are studied in the school physics course. Inertial reference systems are considered to be those with respect to which the material point moves at a constant speed. Newton clarified that any body can be in such a state as long as there is no need to apply forces to it that can change such a state.
In reality, the law of inertia is not fulfilled in all cases. Analyzing examples of inertial and non-inertial frames of reference, consider a person holding onto the handrails in a moving vehicle. When a car brakes sharply, a person automatically moves relative to the vehicle, despite the absence of an external force.
It turns out that not all examples of an inertial frame of reference correspond to the formulation of 1 Newton's law. To clarify the law of inertia, a refined definition of reference systems was introduced in which it is impeccably fulfilled.
Types of reference systems
What reference systems are called inertial? It will become clear soon. "Give examples of inertial reference systems in which 1 Newton's law is satisfied" -a similar task is offered to schoolchildren who have chosen physics as an exam in the ninth grade. In order to cope with the task, it is necessary to have an idea about inertial and non-inertial frames of reference.
Inertia involves the preservation of rest or uniform rectilinear motion of the body as long as the body is in isolation. "Isolated" bodies are those that are not connected, do not interact, are removed from each other.
Let's consider some examples of an inertial frame of reference. Assuming a star in the galaxy as a frame of reference, rather than a moving bus, the implementation of the law of inertia for passengers holding on to the rails will be flawless.
During braking, this vehicle will continue to move uniformly in a straight line until it is affected by other bodies.
What examples of an inertial frame of reference can you give? They should not have a connection with the analyzed body, affect its inertia.
It is for such systems that Newton's 1st law is fulfilled. In real life, it is difficult to consider the movement of a body relative to inertial frames of reference. It is impossible to get to a distant star in order to conduct terrestrial experiments from it.
The Earth is accepted as conditional reference systems, despite the fact that it is associated with objects placed on it.
It is possible to calculate the acceleration in the inertial reference frame if we consider the surface of the Earth as the reference frame. In physics, there is no mathematical record of Newton's 1st law, but it is he who is the basis forderivation of many physical definitions and terms.
Examples of inertial frames of reference
School students sometimes find it difficult to understand physical phenomena. Ninth-graders are offered the task of the following content: “What frames of reference are called inertial? Give examples of such systems. Assume that the cart with the ball initially moves on a flat surface with a constant speed. Then it moves along the sand, as a result, the ball is set into accelerated motion, despite the fact that no other forces act on it (their total effect is zero).
The essence of what is happening can be explained by the fact that while moving on a sandy surface, the system ceases to be inertial, it has a constant speed. Examples of inertial and non-inertial frames of reference 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 figure becomes negative.
Curvilinear movement
Relative to the stars and the Sun, the movement of the Earth is carried out along a curvilinear trajectory, which has the shape of an ellipse. That frame of reference, in which the center is aligned with the Sun, and the axes are directed to certain stars, will be considered inertial.
Note that any frame of reference that will move in a straight line and uniformly relative to the heliocentricsystem is inertial. Curvilinear movement is carried out with some acceleration.
Given the fact that the Earth moves around its axis, the frame of reference, which is associated with its surface, relative to the heliocentric moves with some acceleration. In such a situation, we can conclude that the frame of reference, which is connected with the Earth's surface, moves with acceleration relative to the heliocentric, so 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 relative to it.
To solve practical problems of a technical nature, it is customary to consider as inertial the frame of reference that is rigidly connected with the Earth's surface.
Galilean Relativity
All inertial frames of reference 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 in the same way, regardless of the chosen frame of reference.
Equality of ISO according to 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 ongoing mechanical experiments make it possible to establish whether the frame of reference will be at rest, or whether it makesrectilinear uniform motion. Any system can conditionally be recognized as stationary if the other one at the same time moves relative to it at a certain speed.
- The equations of mechanics remain unchanged with respect to coordinate transformations in the case of transition from one system to another. You can describe the same phenomenon in different systems, but their physical nature will not change.
Problem solving
First example.
Determine if the inertial frame of reference is: a) an artificial satellite of the Earth; b) children's attraction.
Answer. In the first case, there is no question of an inertial reference system, since the satellite moves in orbit under the influence of the force 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 with the elevator. In what situations can it be called inertial? If the elevator: a) falls down; b) moves evenly up; c) rises rapidly d) evenly directed downwards.
Answer. a) In free fall, acceleration appears, so the frame of reference that is associated with the elevator will not be inertial.
b) With uniform movement of the elevator, the system is inertial.
c) When moving with some acceleration, the frame of reference is considered inertial.
d) The elevator moves slowly, has a negative acceleration, so you can’tcall the frame of reference inertial.
Conclusion
Throughout the entire time of its existence, mankind has been trying to understand the phenomena occurring in nature. Attempts to explain the relativity of motion were made by Galileo Galilei. Isaac Newton succeeded in deriving the law of inertia, which began to be used as the main postulate in calculations in mechanics.
At present, the body position detection system includes the body, the device for determining the time, as well as the coordinate system. Depending on whether the body is moving or stationary, it is possible to characterize the position of a certain object in the desired period of time.
