Inertia and Newton's first law presentation. Presentation on the topic "Newton's three laws". Setting the goal of the lesson

• What is the main task of mechanics?

Main task mechanics- determine the position (coordinates) of a moving body at any time.

• Why is the concept of a material point introduced?

In order not to describe the movement of each point of a moving body.

A body whose own dimensions can be neglected under given conditions is called material point.

• When can a body be considered a material point? Give an example.

What is a reference system?

The body of reference, the coordinate system associated with it, and the clock for counting the time of motion form reference system .

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KINEMATICS

Kinematics (Greek "kinematos" - movement) - this is a branch of physics that considers various types of motion of bodies without taking into account the influence of the forces acting on these bodies.

Kinematics answers the question:

"How to describe the movement of the body?"

The main question is why?

Dynamics - a branch of mechanics in which various types of mechanical movements are studied, taking into account the interaction of bodies with each other.

The structure of dynamics.

A change in the speed of a body is always caused by the impact on this body of any other bodies. If no other bodies act on the body, then the speed of the body never changes.

Aristotle:

to maintain a constant speed of the body, it is necessary that something (or someone) acts on it.

Rest relative to the Earth is the natural state of the body, requiring no special cause.

Aristotle

Seem logical statements:

Who is pushing?

Let's take a look at the processes

It is the force that changes the speed of the body

If the force is less, then the speed changes ...

If there is no power, then ...

Strength is not bound with speed , and with speed change

On the basis of experimental studies of the motion of balls on an inclined plane

The speed of any body changes only as a result of its interactions with other bodies.

Galileo Galilei

G. Galileo:

free body, i.e. a body that does not interact with other bodies can keep its speed constant for an arbitrarily long time or be at rest.

Phenomenon preservation of the speed of the body in the absence of other bodies acting on it is called inertia .

Isaac Newton

Newton:

gave a strict formulation of the law of inertia and included it among the fundamental laws of physics as Newton's first law.

(1687 "The Mathematical Principles of Natural Philosophy")

• According to the book: I. Newton. Mathematical principles of natural philosophy. per. from lat. A. N. Krylova. Moscow: Nauka, 1989.

• Every body continues to be held in a state of rest, or uniform and rectilinear motion, until and insofar as it is compelled by applied forces to change this state.

Newton in his work relied on the existence absolute fixed frame of reference, that is, absolute space and time, and this representation modern physics rejects .

Failure to comply with the law of inertia

There are such frames of reference in which the law of inertia is fulfilled will not

Newton's first law:

There are such frames of reference with respect to which bodies keep their speed unchanged if no other bodies act on them. or the action of other bodies is compensated .

Such frames of reference are called inertial.

The resultant is zero

The resultant is zero

inertial frame of reference(ISO) - a frame of reference in which the law of inertia is valid.

I Newton's law is valid only for ISO

Non-inertial frame of reference- an arbitrary reference system that is not inertial.

Examples of non-inertial frames of reference: a frame moving in a straight line with constant acceleration, as well as a rotating frame.

Questions for consolidation:

• What is the phenomenon of inertia?

2. What is Newton's first law?

3. Under what conditions can a body move in a straight line and uniformly?

4. What reference systems are used in mechanics?

1. Rowers trying to get the boat to move against the current can't handle it and the boat stays at rest relative to the shore. The action of what bodies is compensated in this case?

2. An apple lying on a table of a uniformly moving train rolls down when the train brakes sharply. Specify reference systems in which Newton's first law: a) is fulfilled; b) is violated.

3. What kind of experience inside the closed cabin of the ship can determine whether the ship is moving evenly and rectilinearly or is it stationary?

Homework

Everyone: §10, exercise 10.

For those who wish:

prepare messages on the topics:

• "Antique Mechanics"
• "Renaissance Mechanics"
• "I. Newton".

Basic concepts:

Weight; force; ISO.

DYNAMICS

Dynamics. What is he studying?

Description means

LAWS OF DYNAMICS:

• Newton's first law is a postulate about the existence of ISO;

• Newton's second law -

• Newton's third law -

reason change in speed (cause of acceleration)

INTERACTION

LAWS FOR FORCES:

gravity -

elasticity -

BASIC (inverse) problem of mechanics: establishing laws for forces

BASIC (direct) task of mechanics: determination of the mechanical state at any moment of time.

Presentation

on the topic:

Newton's laws

Newton's laws

three laws that underlie classical mechanics and allow writing the equations of motion for any mechanical system if the force interactions for its constituent bodies are known.

Newton's laws- depending on the angle at which you look at them - represent either the end of the beginning or the beginning of the end of classical mechanics.

In any case, this is a turning point in the history of physical science - a brilliant compilation of all the knowledge accumulated by that historical moment about the motion of physical bodies within the framework of physical theory, which is now commonly called classical mechanics.

It can be said that the history of modern physics and the natural sciences in general started from Newton's laws of motion.

Thinkers and mathematicians have been trying for centuries to derive formulas for describing the laws of motion of material bodies.

It never occurred to the ancient philosophers that celestial bodies could move in orbits other than circular ones; at best, the idea arose that planets and stars revolve around the Earth in concentric (that is, nested in each other) spherical orbits.

Why? Yes, because since the time of the ancient thinkers of ancient Greece, it never occurred to anyone that the planets can deviate from perfection, the embodiment of which is a strict geometric circle.

It took the genius of Johannes Kepler to honestly look at this problem from a different angle, analyze the data of real observations and deduce from them that in reality the planets revolve around the Sun in elliptical trajectories.

Imagine something like an athletics hammer - a ball at the end of a string that you spin around your head.

The nucleus in this case does not move in a straight line, but in a circle - which means, according to Newton's first law, something is holding it; this “something” is the centripetal force that you apply to the nucleus, spinning it. In fact, you yourself can feel it - the handle of an athletics hammer noticeably presses on your palms.

If you open your hand and release the hammer, it - in the absence of external forces - will immediately set off in a straight line.

It would be more accurate to say that this is how the hammer will behave in ideal conditions (for example, in outer space), since under the influence of the force of the Earth's gravitational attraction, it will fly strictly in a straight line only at the moment when you release it, and in the future the flight path will be all deviate more towards the earth's surface.

If you try to really release the hammer, it turns out that the hammer released from the circular orbit will set off strictly in a straight line, which is tangent (perpendicular to the radius of the circle along which it was spun) with a linear speed equal to the speed of its circulation along the “orbit”.

Now let's replace the core of the athletics hammer with a planet, the hammer with the Sun, and the string with the force of gravitational attraction:

Here is the Newtonian model of the solar system.

Such an analysis of what happens when one body revolves around another in a circular orbit at first glance seems to be something self-evident, but do not forget that it absorbed a number of conclusions of the best representatives of scientific thought of the previous generation (suffice it to recall Galileo Galilei). The problem here is that when moving along a stationary circular orbit, a celestial (and any other) body looks very serene and appears to be in a state of stable dynamic and kinematic equilibrium. However, if you look at it, only the module (absolute value) of the linear velocity of such a body is preserved, while its direction is constantly changing under the influence of the force of gravitational attraction. This means that the celestial body moves with uniform acceleration. By the way, Newton himself called acceleration "a change in motion."

Newton's first law also plays another important role from the point of view of our scientific attitude to the nature of the material world.

He tells us that any change in the nature of the movement of the body indicates the presence of external forces acting on it.

Relatively speaking, if we observe iron filings, for example, jumping up and sticking to a magnet, or, taking clothes out of the dryer of a washing machine, we find out that things stuck together and dried to one another, we can feel calm and confident: these effects have become a consequence of the action of natural forces (in the examples given, these are the forces of magnetic and electrostatic attraction, respectively).

If Newton's first law helps us determine whether a body is under the influence of external forces, then the second law describes what happens to a physical body under their influence.

The greater the sum of external forces applied to the body, this law says, the greater the acceleration acquires the body. This time. At the same time, the more massive the body, to which an equal sum of external forces is applied, the less acceleration it acquires. This is two. Intuitively, these two facts seem self-evident, and in mathematical form they are written as follows: F=ma

where F - force, m - weight, a - acceleration.

This is probably the most useful and most widely used for applied purposes of all physical equations.

It is enough to know the magnitude and direction of all forces acting in a mechanical system, and the mass of the material bodies of which it consists, and it is possible to calculate its behavior in time with exhaustive accuracy.

It is Newton's second law that gives all classical mechanics its special charm - it begins to seem as if the whole physical world is arranged like the most accurate chronometer, and nothing in it escapes the gaze of an inquisitive observer.

Give me the spatial coordinates and velocities of all material points in the Universe, as if Newton tells us, show me the direction and intensity of all the forces acting in it, and I will predict you any future state of it. And such a view of the nature of things in the Universe existed until the advent of quantum mechanics.

For this law, most likely, Newton earned himself honor and respect from not only natural scientists, but also humanities scientists and simply the general public.

They like to quote him (on business and without business), drawing the widest parallels with what we are forced to observe in our everyday life, and pull almost by the ears to substantiate the most controversial provisions during discussions on any issues, starting with interpersonal and ending with international relations and global politics.

Newton, however, invested in his subsequently called the third law a completely specific physical meaning and hardly conceived it in any capacity other than as an accurate means of describing the nature of force interactions.

Here it is important to understand and remember that Newton is talking about two forces of a completely different nature, and each force acts on “its own” object.

When an apple falls from a tree, it is the Earth that exerts its gravitational attraction on the apple (as a result of which the apple rushes to the Earth's surface with uniform acceleration), but at the same time the apple also attracts the Earth to itself with equal force.

And the fact that it seems to us that it is the apple that falls to the Earth, and not vice versa, is already a consequence of Newton's second law. The mass of an apple compared to the mass of the Earth is low to the point of incomparability, so it is precisely its acceleration that is noticeable to the observer's eyes. The mass of the Earth, in comparison with the mass of an apple, is huge, so its acceleration is almost imperceptible. (In the case of an apple falling, the center of the Earth shifts upward to a distance less than the radius of the atomic nucleus.)

Taken together, Newton's three laws have given physicists the tools they need to begin a comprehensive observation of all phenomena occurring in our universe.

And despite all the tremendous advances in science since Newton, to design a new car or send a spacecraft to Jupiter, you still use Newton's three laws.

Inertial frames of reference Newton's first law

Compiled by: Klimutina N.Yu.

Teacher of MKOU "Pervomaiskaya secondary school" of the Yasnogorsk district of the Tula region

If no forces act on the body, then such a body ALWAYS will be at rest

Aristotle

384 - 322 BC

The body itself can move for an arbitrarily long time with a constant speed. The impact of other bodies leads to its change (increase, decrease or direction)

LAW OF INERTIA

If no other bodies act on the body, the speed of the body does not change.

Galileo Galilei

1564 - 1642

Geocentric frame of reference

from Greek words

"ge" - "earth" "kentron" - "center"

Frames of reference in which the law of inertia is satisfied are called INERTIAL

Heliocentric frame of reference

from Greek words

"helios" - "sun" "kentron" - "center"

Newton's first law

Any body continues to be held in its state of rest or uniform rectilinear motion, until and insofar as it is forced by applied forces to change this state

There are such frames of reference, called inertial ones, with respect to which the body retains its speed unchanged if other bodies do not act on it or the actions of other bodies are compensated

(historical wording)

(modern wording)

Isaac Newton

1643 - 1727

GALILEO'S RELATIVITY PRINCIPLE

In all inertial frames of reference, all mechanical phenomena proceed in the same way for the same

initial conditions

Galileo Galilei

1564 - 1642

FIXING

Lesson summary

Aristotle:

if other bodies do not act on the body, then the body can only rest

A frame of reference is associated with the train. In what cases will it be inertial:

a) the train is at the station;

b) the train leaves the station;

c) the train is approaching the station;

d) the train moves uniformly on a straight line

section of the road?

A car with a running engine moves along a horizontal road in a straight line.

Doesn't this contradict Newton's first law?

Will there be an inertial frame of reference that moves with acceleration relative to some inertial frame?

Galileo:

if other bodies do not act on the body, then the body can not only be at rest, but also move in a straight line and uniformly

Newton:

generalized Galileo's conclusion and formulated the law of inertia (Newton's I law)

Homework

Everyone: §10, exercise 10

Prepare messages on topics:

"Mechanics from Aristotle to Newton"

"The formation of the heliocentric system of the world"

_________________________________________________________

"The Life and Works of Isaac Newton"

Lesson #

Topic: “Inertial reference systems. Newton's I law

Lesson Objectives:

Explain the content of Newton's 1st law.

Form the concept of an inertial frame of reference.

Show the importance of such a section of physics as "Dynamics".

Lesson objectives:

1. Find out what the dynamics section of physics is studying,

2. Learn the difference between inertial and non-inertial frames of reference,

Understand the application of Newton's first law in nature and its physical meaning

During the lesson, a presentation is shown.

During the classes

The content of the lesson stage

Student activities

slide number

Icebreaker "Zerkalo"

Distribute cards, let the children enter the names themselves, put the appraiser

Repetition

What is the main task of mechanics?

Why is the concept of a material point introduced?

What is a reference system? Why is it introduced?

What types of coordinate systems do you know?

Why does a body change its speed?

Uplifting, motivation

1-5

II. new material

Kinematics (Greek "kinematos" - movement) - this is a branch of physics that considers various types of motion of bodies without taking into account the influence of forces acting on these bodies.

Kinematics answers the question:

"How to describe the movement of the body?"

In another section of mechanics - dynamics - the mutual action of bodies on each other is considered, which is the cause of a change in the movement of bodies, i.e. their speeds.

If kinematics answers the question: "how does the body move?", then the dynamics finds out why exactly.

Dynamics is based on Newton's three laws.

If a body lying motionless on the ground begins to move, then it is always possible to detect an object that pushes this body, pulls or acts on it at a distance (for example, if we bring a magnet to an iron ball).

Students study the diagram

Experiment 1

Let's take any body (a metal ball, a piece of chalk or an eraser) in our hands and open our fingers: the ball will fall to the floor.

What body acted on the chalk? (Earth.)

These examples show that a change in the speed of a body is always caused by the impact of some other bodies on the given body. If other bodies do not act on the body, then the speed of the body never changes, i.e. the body will be at rest or moving at a constant speed.

Students perform an experiment, then analyze according to the model, draw conclusions, make notes in a notebook

A mouse click starts the experiment model

This fact is not at all self-evident. It took the genius of Galileo and Newton to realize it.

Starting with the great ancient Greek philosopher Aristotle, for almost twenty centuries, everyone was convinced that in order to maintain a constant speed of the body, it is necessary that something (or someone) act on it. Aristotle considered rest relative to the Earth to be the natural state of the body, requiring no special cause.

In reality, however, a free body, i.e. a body that does not interact with other bodies can keep its speed constant for an arbitrarily long time or be at rest. Only action by other bodies can change its speed. If there were no friction, then the car with the engine off would keep its speed constant.

The first law of mechanics, or the law of inertia, as it is often called, was established by Galileo. But Newton gave a strict formulation of this law and included it among the basic laws of physics. The law of inertia refers to the simplest case of motion - the motion of a body that is not affected by other bodies. Such bodies are called free bodies.

An example of reference systems in which the law of inertia is not fulfilled is considered.

Students write in notebooks

Newton's first law is stated as follows:

There are such frames of reference with respect to which bodies keep their speed unchanged if no other bodies act on them.

Such frames of reference are called inertial (ISO).

Cards are distributed in groups

consider the following examples:

Characters of the fable "Swan, cancer and pike"

body floating in liquid

An airplane flying at a constant speed

Students draw a poster where they indicate the forces acting on the body. Poster protection

In addition, it is impossible to put a single experiment that would show in its pure form how a body moves if other bodies do not act on it (Why?). But there is one way out: it is necessary to put the body in conditions under which the influence of external influences can be made less and less, and observe what this leads to.

The phenomenon of maintaining the speed of a body in the absence of the action of other bodies on it is called inertia.

III. Consolidation of the studied

Questions for consolidation:

What is the phenomenon of inertia?

What is Newton's first law?

Under what conditions can a body move in a straight line and uniformly?

What reference systems are used in mechanics?

Students answer questions

Rowers trying to get the boat to move against the current cannot cope, and the boat remains at rest relative to the shore. The action of what bodies is compensated in this case?

An apple lying on the table of a uniformly moving train rolls down when the train brakes sharply. Specify reference systems in which Newton's first law: a) is fulfilled; b) is violated. (In the reference frame associated with the Earth, Newton's first law holds. In the reference frame associated with the wagons, Newton's first law does not hold.)

What experience inside the closed cabin of the ship can determine whether the ship is moving evenly and rectilinearly or standing still? (None.)

Tasks and strengthening exercises:

In order to consolidate the material, a number of qualitative tasks on the studied topic can be proposed, for example:

1. Can a puck thrown by a hockey player move uniformly along
ice?

2. Name the bodies whose action is compensated in the following cases: a) an iceberg floats in the ocean; b) the stone lies at the bottom of the stream; c) the submarine drifts uniformly and rectilinearly in the water column; d) the balloon is held near the ground by ropes.

3. Under what condition will a steamboat sailing against the current have a constant speed?

We can also propose a number of slightly more complex tasks on the concept of an inertial frame of reference:

1. The frame of reference is rigidly connected with the elevator. In which of the following cases can the frame of reference be considered inertial? Elevator: a) falls freely; b) moves uniformly upwards; c) is moving rapidly upwards; d) moves slowly up; d) moves steadily down.

2. Can a body at the same time in one frame of reference maintain its speed, and in another - change? Give examples to support your answer.

3. Strictly speaking, the frame of reference associated with the Earth is not inertial. Is it due to: a) gravity of the Earth; b) the rotation of the Earth around its axis; c) the movement of the earth around the sun?

And now let's check your knowledge that you received today in the lesson

Mutual check, answers on the screen

Students answer questions

Students take a test

Test in Excel format

(TEST. xls)

Homework

Learn §10, write down the questions at the end of the paragraph;

Complete exercise 10;

Those who wish: to prepare reports on the topics "Antique mechanics", "Renaissance mechanics", "I. Newton".

Students make notes in their notebooks.

List of used literature

Butikov E.I., Bykov A.A., Kondratiev A.S. Physics for university applicants: Textbook. - 2nd ed., Rev. – M.: Nauka, 1982.

Golin G.M., Filonovich S.R. Classics of physical science (from ancient times to the beginning of the 20th century): Ref. allowance. - M .: Higher School, 1989.

Gromov S. V. Physics Grade 10: Textbook for grade 10 general educational institutions. – 3rd ed., stereotype. - M .: Enlightenment 2002

Gursky I.P. Elementary Physics with Examples of Problem Solving: Textbook / Ed. Savelyeva I.V. - 3rd ed., revised. – M.: Nauka, 1984.

Feathers A. V. Gutnik E. M. Physics. 9th grade: A textbook for general educational institutions. - 9th ed., stereotype. – M.: Bustard, 2005.

Ivanova L.A. Activation of cognitive activity of students in the study of physics: A guide for teachers. – M.: Enlightenment, 1983.

Kasyanov V.A. Physics. 10th grade: Textbook for general educational institutions. – 5th ed., stereotype. – M.: Bustard, 2003.

Kabardi O. F. Orlov V. A. Zilberman A. R. Physics. Task book 9-11 cells

Kupershtein Yu.S. Physics Basic abstracts and differentiated problems 10th grade Petersburg, BHV 2007

Methods of teaching physics in high school: Mechanics; teacher's guide. Ed. E.E. Evenchik. Second edition, revised. – M.: Enlightenment, 1986.

Peryshkin A. V. Physics. 7th grade: A textbook for general educational institutions. - 4th ed., corrected. - M .: Bustard, 2001

Proyanenkova L. A. Stefanova G. P. Krutova I. A. Lesson planning for the textbook Gromova S. V., Rodina N. A. "Physics 7 cells" M.: "Exam", 2006

Modern physics lesson in secondary school / V.G. Razumovsky, L.S. Khizhnyakova, A.I. Arkhipova and others; Ed. V.G. Razumovsky, L.S. Khizhnyakova. – M.: Enlightenment, 1983.

Fadeeva A.A. Physics. Workbook for grade 7 M. Genzher 1997

Internet resources:

educational electronic publication PHYSICS grade 7-11 practice

Physics 10-11 Preparation for the exam 1C education

Library of electronic visual aids - Kim

Physics library of visual aids 7-11 grades 1C education

As well as pictures on request from http://images.yandex.ru