Mechanical movement. Reference system. Moving. Presentation "material point. Reference system" presentation for a lesson in physics (grade 9) on the topic Summary material point reference system

The purpose of the lesson: To give an idea of kinematics; to acquaint with the goals and objectives of the physics course; introduce concepts: mechanical movement, trajectory, path; prove that rest and movement are relative concepts; substantiate the necessity of introducing an idealized model - a material point, a frame of reference.

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Topic: "Material point. Reference system"

Objectives: 1. to give an idea of the kinematics;

2. to acquaint students with the goals and objectives of the physics course;

3. to introduce the concepts: mechanical movement, trajectory, path; prove that rest and movement are relative concepts; substantiate the necessity of introducing an idealized model - a material point, a frame of reference.

4. Learning new material.

During the classes

1. Introductory conversation with students about the goals and objectives of the course of physics in grade 9.

What does kinematics study? dynamics?

What is the main task of mechanics?

What phenomena should be able to explain?

A problematic experiment.

Which body falls faster: a sheet of paper or a book?

Which body falls faster: an unfolded sheet of paper or the same sheet folded several times?

Why doesn't water flow out of the hole in the jar when the jar falls?

What happens if you put a bottle of water on the edge of a sheet of paper and jerk it horizontally? If you pull the paper slowly?

2. Examples of bodies at rest and in motion. Demonstrations.

О Roll of the ball on an inclined plane.

О The movement of the ball up an inclined plane.

О Moving the cart on the display table.

H. Formation of concepts: mechanical movement, body trajectory, rectilinear and curvilinear movements, traversed path.

Demonstrations.

O Movement of a hot flashlight bulb in a darkened auditorium.

О A similar experiment with a light bulb mounted on the rim of a rotating disc.

4. Formation of ideas about the frame of reference and the relativity of motion.

1. Problem experiment.

The movement of the cart with the bar on the demonstration table.

Is the bar moving?

Is the question clear enough? Formulate the question correctly.

2. Frontal experiment to observe the relativity of motion.

Place your ruler on a piece of paper. Press one end of the ruler with your finger and use a pencil to move it to a certain angle in the horizontal plane. In this case, the pencil should not move relative to the ruler.

What is the trajectory of the end of the pencil relative to the sheet of paper?

What kind of movement does the pencil movement refer to in this case?

What is the state of the end of the pencil in relation to the sheet of paper? About the ruler?

a) It is necessary to introduce a reference system as a set of a reference body, a coordinate system and an instrument for determining time.

b) The trajectory of the body depends on the choice of the frame of reference.

5. Justification of the need to introduce an idealized model - a material point.

6. Acquaintance with the forward movement of the body.

Demog9soiration.

F Movements of a large-sized book with a line drawn on it (Fig. 2) (The peculiarity of the movement is that any straight line drawn in the body remains parallel to itself)

Movement of a torch smoldering from both ends in a darkened auditorium.

7. Solution main task mechanics: determining the position of the body at any time.

a) On a straight line - a one-dimensional coordinate system (car on a highway).

X = 300 m, X = 200 m

b) On a plane - a two-dimensional coordinate system (ship at sea).

c) In space - a three-dimensional coordinate system (airplane in the sky).

Ts. Solution of quality problems.

Answer the questions in writing (yes or no):

When calculating the distance from the Earth to the Moon?

When measuring its diameter?

When a spacecraft lands on its surface?

When determining the speed of its movement around the Earth?

Going from home to work?

Performing gymnastic exercises?

Taking a boat trip?

And when measuring a person's height?

III. Historical information.

Galileo Galilei, in his book Dialogue, cites vivid example trajectory relativity: "Imagine an artist who is on a ship sailing from Venice across the Mediterranean. The artist draws on paper with a pen a whole picture of figures drawn in thousands of directions, depicting countries, buildings, animals and other things .." The trajectory of the pen in relation to the sea, Galileo represents "a line of extension from Venice to the final place ...

more or less wavy, depending on how much the ship swayed along the way. "

IV. Lesson summary.

V. Homework: §1, exercise 1 (1-3).

Topic: "Moving"

Purpose: 1. to substantiate the need to introduce a displacement vector to determine the position of the body in space;

2. to form the ability to find the projection and module of the displacement vector;

3. repeat the rule of addition and subtraction of vectors.

During the classes

1. Actualization of knowledge.

Frontal poll.

1. What does mechanics study?

2. What movement is called mechanical?

3. What is the main task of mechanics?

4. What is called a material point?

5 What movement is called translational?

b. What section of mechanics is called kinematics?

7. Why is it necessary to single out special reference bodies when studying mechanical motion?

8. What is called a frame of reference?

9. What coordinate systems do you know?

10. Prove that movement and rest are relative concepts.

11. What is called a trajectory?

12. What types of trajectory do you know?

13. Does the trajectory of the body depend on the choice of the frame of reference?

14. What are the movements depending on the shape of the trajectory?

15. What is the path traveled?

Solving quality problems.

1. The cyclist moves evenly and in a straight line. depict the trajectories of movement:

a) the center of the bicycle wheel relative to the road;

b) points of the wheel rim relative to the center of the wheel;

c) points of the wheel rim relative to the bicycle frame;

d) points of the wheel rim relative to the road.

2. Which coordinate system should be selected (one-dimensional, two-dimensional, three-dimensional) to determine the position of the following bodies:

a) a chandelier in the room, e) a submarine,

b) train, f) chess piece,

c) helicopter, g) plane in the sky

d) an elevator, h) an airplane on the runway.

1. Justification of the need to introduce the concept of a displacement vector.

a) Problem. Determine the final position of the body in space if it is known that the body left point A and passed a distance of 200 m?

b) Introduction of the concept of the displacement vector (definition, designation), modulus of the displacement vector (designation, unit of measurement). Difference between displacement vector modulus and distance traveled. When do they match?

2. Formation of the concept of projection of the displacement vector. When is a projection considered positive and when is it negative? When is the projection of the displacement vector equal to zero? (Fig. 1)

H. Addition of vectors.

a) The triangle rule. To add two movements, the beginning of the second movement should be aligned with the end of the first. The closing side of the triangle will be the total displacement (Fig. 2).

b) The rule of the parallelogram. Build a parallelogram on the vectors of the added displacements S1 and S2. The diagonal of the parallelogram OD will be the resulting displacement (Fig. 3).

4. Frontal experiment.

a) Put a square on a sheet of paper, put points D, E and A near the sides of the right angle (fig. 4).

b) Move the end of the pencil from point 1) to point E, leading it along the sides of the triangle in the direction 1) A B E.

c) Measure the path with the drawn end of the pencil relative to the sheet of paper.

d) Construct a vector of displacement of the end of the pencil relative to the sheet of paper.

E) Measure the modulus of the displacement vector and the distance traveled with the end of a pencil and compare them.

III. Solving problems. -

1. Do we pay for the journey or travel when traveling by taxi or by plane?

2. The dispatcher, taking the car at the end of the working day, made a note in the waybill: "Increase in the meter reading 330 km". What is this entry about: the distance traveled or the movement?

H. The boy threw the ball up and caught it again. Assuming that the ball has risen to a height of 2.5 m, find the path and movement of the ball.

4. The elevator car descended from the eleventh floor of the building to the fifth, and then went up to the eighth floor. Assuming that the distance between floors is 4 m, determine the path and movement of the car.

IV. Lesson summary.

V. homework: § 2, exercise 2 (1,2).

Topic: "Determination of the coordinates of a moving body"

1. to form the ability to solve the main problem of mechanics: find the coordinates of the body at any time;

2. determine the value of the projections of the displacement vector on the coordinate axis and its modulus.

During the classes

1. Updating knowledge

Frontal poll.

What quantities are called vector? Give examples of vector quantities.

What are called scalar quantities? What is called displacement? How do the displacements stack up? What is called the projection of a vector onto a coordinate axis? When is a vector's projection positive? negative?

What is called a vector module?

Solving problems.

1. Determine the signs of the projections of the displacement vectors S1, S2, S3, S4, S5, S6 on the coordinate axes.

2. The car drove along the street a path equal to 400 m. Then it turned right and drove along the lane for another 300 m. Considering the movement to be straightforward on each of the sections of the path, find the path and movement of the cars. (700 m; 500 m)

H. The minute hand of the clock makes a full revolution in one hour. What path does the end of the 5 cm arrow travel through? What is the linear displacement of the end of the arrow? (0.314 m; 0)

11. Learning new material.

Solution of the main problem of mechanics. Determination of the coordinates of a moving body.

III. Solving problems.

1. In fig. 1 shows the initial position of point A. Determine the coordinate of the end point, build a displacement vector, determine its modulus, if $ x = 4m and $ y = 3m.

2. The coordinates of the beginning of the vector are equal: X1 = 12 cm, Y1 = 5 cm; end: X2 = 4 cm, Y2 = 11 cm. Construct this vector and find its projection on the coordinate axis and the modulus of the vector (Sх = -8, Sу = 6 cm, S = 10 cm). (On one's own.)

H. The body moved from a point with coordinates X0 = 1 m, Y0 = 4 m to a point with coordinates X1 = 5 m, Y1 = 1 m. Find the modulus of the vector of displacement of the body in its projection on the coordinate axis (Sх = 4m, Sу = - 3 cm, S = 5 m).

IV. Lesson summary.

V. Homework: 3, exercise 3 (1-3).

Topic: "Rectilinear uniform motion"

1. to form the concept of rectilinear uniform motion;

2. to find out the physical meaning of the speed of movement of the body;

3. to continue the formation of the ability to determine the coordinates of a moving body, to solve problems graphically and analytically.

During the classes

Knowledge update.

Physical dictation

1. Mechanical movement is a change ...

2. The material point is the body ...

3. The trajectory is a line ...

4. The traversed path is called ...

5. The frame of reference is ...

b. The displacement vector is a line segment ...

7. The modulus of the displacement vector is ...

8. The vector projection is considered positive if ...

9. The vector projection is considered negative if ...

10. The projection of the vector is equal to O, if the vector ...

11. The equation for finding the coordinates of the body at any time has the form ...

II. Learning new material.

1. Determination of rectilinear uniform motion. Vector character of speed. Velocity projection in one-dimensional coordinate system.

2. Formula of displacement. Time dependence of movement.

H. Coordinate equation. Determination of the coordinates of the body at any time.

4. International system of units

Length unit - meter (m),

Time unit - second (s),

The unit of speed is meter per second (m / s).

1 km / h = 1 / 3.6 m / s

Im / s = 3.6 km / h

Historical information.

Old Russian measures of length:

1 vershok = 4.445 cm

1 arshin = 0.7112m,

1 fathom = 2, IЗЗбм,

1 verst = 1.0668 km,

1 Russian mile = 7.4676 km.

English measures of length:

1 inch = 25.4 mm,

1 foot = 304.8 mm,

1 overland mile = 1609 m,

1 nautical mile 1852.

5. Graphic representation of movement.

The graph of the dependence of the projection of speed on the change in movement.

The graph of the dependence of the module of the projection of speed.

The graph of the dependence of the projection of the displacement vector on the time of movement.

The graph of the dependence of the module of the projection of the displacement vector on the time of movement.

Graph I - the direction of the velocity vector coincides with the direction of the coordinate axis.

Graph I I - the movement of the body occurs in the direction opposite to the direction of the coordinate axis.

6.Sх = Vхt. This product is numerically equal to the area of the shaded rectangle (Fig. 1).

7. Historical background.

Speed charts were first introduced in the middle of the 11th century by the archdeacon of Rouen Cathedral, Nicolas Orem.

III. Solving graphic problems.

1. In fig. 5 shows the graphs of the projection of vectors of two cyclists moving along parallel lines.

Answer the questions:

What can be said about the direction of movement of cyclists in relation to each other?

Who is moving faster?

Draw a graph of the dependence of the projection modulus of the displacement vector on the time of movement.

What is the distance covered by the first cyclist in 5 seconds of movement?

2. The tram moves at a speed of 36 km / h, and the speed vector coincides with the direction of the coordinate axis. Express this speed in meters per second. Draw a graph of the dependence of the projection of the velocity vector on the time of movement.

IV. Lesson summary.

V. homework: § 4, exercise 4 (1-2).

Topic: "Rectilinear uniformly accelerated motion. Acceleration"

1. to introduce the concept of uniformly accelerated motion, a formula for the acceleration of a body;

2. explain its physical meaning, introduce the unit of acceleration;

3. to form the ability to determine the acceleration of the body with uniformly accelerated and equally slowed movements.

During the classes

1. Actualization of knowledge (frontal survey).

Give the definition of uniform rectilinear motion.

What is called the speed of uniform movement?

What is the unit of speed in the International System of Units?

Write down the formula for the projection of the velocity vector.

In what cases is the projection of the velocity vector of uniform motion onto the axis positive, in which - negative?

Write the formula of the day of the projection of the travel vector?

What is the coordinate of a moving body at any given time?

How is speed expressed in kilometers per hour expressed in meters in seconds and vice versa?

The Volga car is moving at a speed of 145 km / h. What does this mean?

11. Independent work.

1. How much is the speed of 72 km / h more than the speed of 10 m / s?

2. The speed of the artificial Earth satellite is 3 km / h, and the rifle bullet is 800 m / s. Compare these speeds.

3 With a uniform movement, a pedestrian covers a path of 12 m in b s. What path will he take when moving at the same speed in 3 s?

4. Figure 1 shows a graph of the dependence of the distance traveled by a cyclist on time.

Determine the cyclist's speed.

Plot the module versus travel time.

II. Learning new material.

1. A repetition of the concept of uneven rectilinear motion from a physics course? class.

How can you determine the average speed of movement?

2. Acquaintance with the concept of instantaneous speed: the average speed for a very small finite period of time can be taken as instantaneous, the physical meaning of which is that it shows at what speed the body would move if, starting from a given moment in time, its motion became uniform and straightforward.

Answer the question:

What speed are we talking about in the following cases?

o The speed of the Moscow - Leningrad courier train is 100 km / h.

o The passenger train passed the traffic light at a speed of 25 km / h.

H. Demonstration of experiments.

a) Rolling the ball along an inclined plane.

b) On an inclined plane along its entire length, reinforce the paper tape. Place an easily movable drip cart on the board. Release the cart and examine the arrangement of the drops on the paper.

4. Determination of uniformly accelerated motion. Acceleration: definition, physical meaning, formula, unit of measurement. The acceleration vector and its projection onto the axis: in which case is the acceleration projection positive, in which - negative?

a) Equally accelerated motion (speed and acceleration are in the same direction, the modulus of speed increases; ax> O).

b) Equally slow motion (speed and acceleration are directed in opposite directions, the speed module decreases, ah

5. Examples of accelerations encountered in life:

Suburban electric train 0.6 m / s2.

The IL-62 aircraft with a take-off run of 1.7 m / s2.

The acceleration of a freely falling body is 9.8 m / s2.

Rocket at satellite launch 60 m / s.

A bullet in the barrel of a Kalashyavkov submachine gun, yu5 m / s2.

6. Graphical representation of acceleration.

Graph I - corresponds to uniformly accelerated motion with acceleration a = 3 m / s2.

Graph II - corresponds to uniformly slow motion with acceleration

III. Solving problems.

An example of problem solving.

1. The speed of a car moving in a straight line and evenly increased from 12 m / s to 24 m / s in 6 seconds. What is car acceleration?

Solve the following tasks using the example.

2. The car was moving uniformly, and within 10 s its speed increased from 5 to 15 m / s. Find the acceleration of the car (1 m / s2)

H. When braking, the vehicle speed decreases from 20 to 10 m / s for 5 s. Find the acceleration of the car, provided that it remained constant while driving (2 m / s2)

4. Acceleration of a passenger aircraft during takeoff lasted 25 seconds, by the end of acceleration the aircraft had a speed of 216 km / h. Determine aircraft acceleration (2.4 m / s2)

IV. Lesson summary.

V. Homework: § 5, exercise 5 (1 - З).

Topic: "The speed of rectilinear uniformly accelerated motion"

1. enter a formula for determining the instantaneous speed of a body at any time;

2. to continue the formation of the ability to build graphs of the dependence of the projection of speed on time;

3. calculate the instantaneous speed of the body at any given time.

During the classes

Independent work.

Option 1

1. What motion is called uniformly accelerated?

2. Write down the formula to determine the projection of the acceleration vector.

H. The acceleration of a body is 5 m / s2, what does this mean?

4. The descent speed of the parachutist after opening the parachute decreased from 60 to 5 m / s in 1.1 s. Find the skydiver's acceleration. (50m / s2)

Option II

1 What is called acceleration?

2.What is the name of the acceleration units?

H. Acceleration of the body is equal to 3 m / s2. What does this mean?

4. With what acceleration does the car move if in 10 seconds its speed has increased from 5 to 10 m / s? (0.5 m / s2)

II. Learning new material.

1. Derivation of a formula for determining the instantaneous speed of a body at any time.

1. Actualization of knowledge.

a) The graph of the dependence of the projection of the velocity vector on the time of movement Y (O.

2. Graphic representation of movement. -

III. Solving problems.

Examples of problem solving.

1. The train is moving at a speed of 20 m / s. When the brakes were applied, it began to move with a constant acceleration of 0.1 m / s2. Determine the speed of the train through the ZO from after the start of movement.

2. The speed of the body is given by the equation: V = 5 + 2 t (units of speed and acceleration are expressed in SI). What are the initial velocity and acceleration of the body? Plot the body speed and find the speed at the end of the fifth second.

Solve problems by pattern

1. The car, the speed of which is 10 m / s, began to move with a constant acceleration of 0.5 m / s2, directed in the same direction as the velocity vector. Determine the vehicle speed after 20 seconds. (20 m / s)

2. The projection of the speed of a moving body changes according to the law

V x = 10 -2t (values are measured in SI). Define:

a) projection of the initial speed, module and direction of the initial speed vector;

b) projection of acceleration, module and direction of the acceleration vector;

c) build a graph of dependence Vx (t).

IV. Lesson summary.

V Homework: § 6, exercise 6 (1 - 3); to compose questions of mutual control to §6 of the textbook.

Topic: "Moving with rectilinear uniformly accelerated motion"

1. to acquaint students with the graphical way of deriving the formula for displacement with rectilinear uniformly accelerated motion;

2. to form the ability to determine the movement of the body using the formulas:

During the classes

Knowledge update.

Two students come to the blackboard and ask each other questions prepared in advance on the topic. The rest of the students act as experts: they assess the performance of the students. Then the next couple is invited, etc.

II. Solving problems.

1. In fig. 1 is a graph showing the dependence of the speed module on time. Determine the acceleration of a rectilinear moving body.

Figure 2. 2 shows a graph of the dependence of the projection of the speed of rectilinear motion of the body on time. Describe the nature of the movement in certain areas. Plot the projected acceleration versus travel time.

Sh. Study of new material.

1. Derivation of the formula for displacement at uniformly accelerated motion in a graphical way.

a) The path traversed by the body in time is numerically equal to the area of the trapezium ABC

b) Breaking the trapezoid into a rectangle and a triangle, we find the area of these figures separately:

III. Solving problems.

An example of solving the problem.

A cyclist moving at a speed of 3 m / s begins to descend the mountain with an acceleration of 0.8 m / s2. Find the length of the mountain, if the skiusk took 6 s,

Solve problems using a model.

1. The bus moves at a speed of 36 km / h. At what minimum distance from the stop should the driver start to brake if, for the convenience of passengers, the acceleration during braking of the bus should not exceed 1.2 m / s? (42 m)

2. The space rocket is launched from the cosmodrome with acceleration

45 m / s2. What speed will it have after it has flown 1000 m? (300 m / s)

3. A sled is rolled down a 72 m long mountain for 12 seconds. Determine their speed at the end of the path. The initial speed of the sled is zero. (12m / s)

Today we will talk about the systematic study of physics and its first section - mechanics. Physics studies different types changes or processes occurring in nature, and what processes were primarily of interest to our ancestors? Of course, these are processes associated with movement. They wondered if the spear they had thrown would fly, and if it would hit the mammoth; they wondered if the messenger would have time to reach a nearby cave before sunset with the important news. All these types of movement and mechanical movement in general are studied by the section called mechanics.

Wherever we look, there are a lot of examples of mechanical movement around us: something rotates, something jumps up and down, something moves back and forth, and other bodies can be at rest, which is also an example of mechanical movement. whose speed is zero.

Definition

Mechanical movement is called the change in the position of bodies in space relative to other bodies over time (Fig. 1).

Rice. 1. Mechanical movement

As physics is divided into several sections, mechanics has its own sections. The first one is called kinematics. Mechanics section kinematics answers the question of how the body moves. Before starting to work on the study of mechanical movement, it is necessary to define and learn the basic concepts, the so-called ABC of kinematics. In the lesson we will learn:

Choose a frame of reference for studying body movement;

Simplify tasks by mentally replacing the body with a material point;

Determine the trajectory of movement, find the way;

Distinguish the types of movements.

In the definition of mechanical movement, the expression regarding other bodies... We always need to choose the so-called reference body, that is, the body relative to which we will consider the movement of the object we are examining. A simple example: move your hand and tell me - does it move? Yes, of course, in relation to the head, but in relation to the button on your shirt, it will be immovable. Therefore, the choice of reference is very important, because relative to some bodies, movement occurs, but relative to other bodies, movement does not occur. Most often, a body is chosen as the reference body, which is always under the hands, more precisely, under the feet - this is our Earth, which is the reference body in most cases.

For a long time, scientists have argued about whether the Earth revolves around the Sun or the Sun revolves around the Earth. In fact, from the point of view of physics, from the point of view of mechanical movement, this is just a dispute about the reference body. If the Earth is considered the reference body, then yes - the Sun revolves around the Earth, if the Sun is considered the reference body - then the Earth revolves around the Sun. Therefore, the reference body is an important concept.

How to describe the change in body position?

To accurately set the position of the body of interest to us relative to the reference body, it is necessary to associate a coordinate system with the reference body (Fig. 2).

When the body moves, the coordinates change, and in order to describe their change, we need a device for measuring time. To describe movement, you need to have:

Reference body;

The coordinate system associated with the reference body;

A device for measuring time (clock).

All these objects together make up a frame of reference. Until we have chosen a frame of reference, it makes no sense to describe mechanical motion - we will not be sure of how the body moves. A simple example: a suitcase lying on a shelf in a train compartment, which is moving, simply rests for a passenger, and moves for a person standing on the platform. As we can see, one and the same body both moves and rests, the whole problem is that the frames of reference are different (Fig. 3).

Rice. 3. Various reporting systems

Dependence of the trajectory on the choice of the frame of reference

Let's answer an interesting and important question, whether the shape of the trajectory and the path traversed by the body depend on the choice of the frame of reference. Consider a situation when there is a train passenger with a glass of water on the table next to him. What will be the trajectory of the glass in the reporting system associated with the passenger (the reference body is the passenger)?

Of course, the glass is motionless relative to the passenger. This means that the trajectory is a point, and the displacement is equal (Fig. 4).

Rice. 4. Trajectory of the glass relative to the passenger on the train

What will be the trajectory of the glass relative to the passenger who is waiting for the train on the platform? For this passenger it will seem that the glass is moving in a straight line and has a nonzero path (Fig. 5).

Rice. 5. Trajectory of the glass relative to the passenger on the apron

From the above, we can conclude that the trajectory and path depend on the choice of the frame of reference.

In order to describe mechanical movement, first of all, it is necessary to determine the frame of reference.

We study motion in order to predict where this or that object will be at the required moment in time. The main task of mechanics- determine the position of the body at any time. What does it mean to describe the movement of a body?

Consider an example: a bus travels from Moscow to St. Petersburg (Fig. 6). Is the size of the bus important to us compared to the distance it will cover?

Rice. 6. The movement of the bus from Moscow to St. Petersburg

Of course, the size of the bus in this case can be neglected. We can describe the bus as one moving point, in another way it is called a material point.

Definition

A body whose dimensions can be neglected in this problem is called material point.

One and the same body, depending on the conditions of the problem, may or may not be a material point. When moving a bus from Moscow to St. Petersburg, the bus can be considered a material point, because its dimensions are incomparable with the distance between cities. But if a fly flew into the passenger compartment of the bus and we want to investigate its movement, then in this case the dimensions of the bus are important to us, and it will no longer be a material point.

Most often in mechanics, we will study precisely the movement of a material point. During its movement, a material point successively passes a position along a certain line.

Definition

The line along which the body (or material point) moves is called body trajectory ( rice. 7).

Rice. 7. Point trajectory

Sometimes we observe the trajectory (for example, the process of grading a lesson), but more often than not, the trajectory is some kind of imaginary line. With the availability of measuring instruments, we can measure the length of the trajectory along which the body moved, and determine the value, which is called path(fig. 8).

Definition

Path traversed by the body in some time is trajectory segment length.

Rice. 8. Way

There are two main types of movement - straight and curved movement.

If the trajectory of the body is a straight line, then the movement is called rectilinear. If the body moves along a parabola or along any other curve, we are talking about curvilinear motion. When considering the motion of not just a material point, but the motion of a real body, two more types of motion are distinguished: translational motion and rotational motion.

Translational and rotational movement. Example

What movements are called translational, and what are rotational? Let's look at this issue using the Ferris wheel as an example. How does the Ferris wheel's cabin move? Let's mark two arbitrary points of the car and connect them with a straight line. The wheel is turning. After a while, mark the same points and connect them. The resulting lines will lie on parallel lines (Fig. 9).

Rice. 9. The translational movement of the Ferris wheel cabin

If a straight line drawn through any two points of the body remains parallel to itself during movement, then such motion are called progressive.

Otherwise, we are dealing with a rotational motion. If the straight line were not parallel to you, the passenger would most likely fall out of the wheel cabin (Fig. 10).

Rice. 10. Rotational movement of the wheel cabin

Rotational is called such a movement of a body in which its points describe circles lying in parallel planes. The straight line connecting the centers of the circles is called axis of rotation.

Very often we have to deal with a combination of translational and rotational motion, the so-called translational-rotational motion. The simplest example of such a movement is the movement of a diver into the water (Fig. 11). It performs a rotation (somersault), but at the same time its center of mass moves forward in the direction of the water.

Rice. 11. Translational-rotational movement

Today we have studied the ABC of kinematics, that is, the basic, most important concepts, which in the future will allow us to move on to solving the main problem of mechanics - determining the position of the body at any moment in time.

Bibliography

Tikhomirova S.A., Yavorskiy B.M. Physics (basic level) - M .: Mnemosina, 2012.
Gendenshtein L.E., Dick Yu.I. Physics grade 10. - M .: Mnemosina, 2014.
Kikoin I.K., Kikoin A.K. Physics - 9, Moscow, Education, 1990.

Internet portal "Av-physics.narod.ru" ().
Internet portal "Rushkolnik.ru" ().
Internet portal "Testent.ru" ().

Homework

Think about what is the reference body when we say:

the book lies motionless on a table in the compartment of a moving train;
a stewardess after takeoff passes through the passenger cabin of the aircraft;
The earth rotates on its axis.

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FUNDAMENTALS OF KINEMATICS Lesson 1. THEME: “Material point. Reference system "

Mechanics is a branch of physics that studies motion. The main task of mechanics is to determine the position of a body in space at any time.

Kinematics is a section of mechanics that studies ways of describing movement and the relationship between the quantities that characterize this movement. Dynamics is a branch of mechanics that studies the causes of mechanical movement. Statics studies the laws of equilibrium of a system of bodies.

Mechanical movement is a change in the position of a body in space over time relative to other bodies.

Translational movement is a movement in which all points of the body move in the same way, at the same speed. A material point is a body whose dimensions can be neglected, in the conditions of a given problem being solved. Reference body - any body conditionally taken as motionless, relative to which the movement of other bodies is considered.

For example, the Earth is very often considered for a material point, if its movement around the Sun is investigated.

For example, But if we are solving a problem related to the daily rotation of the planets, then it is necessary to take into account the shape and size of the planet. For example, if you want to determine the time of sunrise at different places the globe.

What is translational motion? The body moves forward if all its points move in the same way. or A body moves translationally if a straight line drawn through two points of this body, when it moves, shifts parallel to its original position.

Examples of translational motion

To determine the position of a body (material point) in space, you need to: set the reference body; select a coordinate system; have a device for counting time (clock)

The reference body, the associated coordinate system and the clock for counting the time of movement form a reference system.

What is a reference body? The reference body is a body relative to which the position of other (moving) bodies is determined. For example, it can be a tree, when we consider the movement of a bus, or Earth, when calculating the movement of a rocket.

Coordinate system The position of a body in space can be determined using 2 coordinates (two-dimensional coordinate system) The position of a body in space can be determined using 3 coordinates (three-dimensional coordinate system)

With the rectilinear motion of the body, one coordinate axis is sufficient

Trajectory - the line along which the body moves.

Path - the length of the path. [L] Displacement is a vector drawn from the initial position of a material point to its final position.

On the subject: methodological developments, presentations and notes

Dynamics. Inertial frames of reference. Newton's first law.

Lesson objectives: to form the concept of ISO; study Newton's first law; show the importance of such a section of physics as "Dynamics"; foster a sense of respect for various professions ...

lesson summary "Movement. Material point. Reference system. Relativity of movement."

This work can be used when studying the topic in the 9th grade: "Kinematics". The material is intended to repeat and summarize the topic. The work can be used as a repetition of the material ...

Lesson for grade 9 on the topic “Material point. Reference system "

The purpose of the lesson: to form students about the material point; to form in students the skill of identifying situations in which the concept of a material point can be applied; to form students' understanding of the frame of reference; consider the types of frames of reference.

LESSON PLAN:

5. Homework (1 min)

DURING THE CLASSES:

1. Organizational stage (1 min)

At this stage, there is a mutual greeting of the teacher and students; checking for those who are absent from the journal.

2. Motivational stage (5 min)

Today in the lesson we have to return to the study of mechanical phenomena. In the 7th grade, we already encountered mechanical phenomena and before starting to study new material, let's remember:

- What is mechanical movement?

- What is uniform mechanical motion?

- What is speed?

- What is average speed?

- How to determine the speed if we know the distance and time?

In the 7th grade, you and I solved fairly simple problems of finding the path, time or speed of movement. If you remember, the most difficult task was to find the average speed.

This year we will take a closer look at what types of mechanical movement exist, how to describe any kind of mechanical movement, what to do if the speed changes during movement, etc.

Already today we will get acquainted with the basic concepts that help to describe both quantitatively and qualitatively mechanical movement. These concepts are very handy tools when considering any kind of mechanical movement.

We write the number and the topic of the lesson “Material point. Reference system "

Today in the lesson we have to answer the questions:

- What is a material point?

- Is it always possible to apply the concept of a material point?

- what is a frame of reference?

- What does the frame of reference consist of?

- What types of frames of reference exist?

3. Learning new material (25 min)

Everything in the world around us is in continuous motion. What is meant by the word "Movement"?

Movement is any change that takes place in the surrounding world.

Most simple form movement is already known to us mechanical movement.

When solving any problems related to mechanical movement, it is necessary to be able to describe this movement. What does it mean to “describe the movement of the body”?

This means that you need to determine:

1) the trajectory of movement;

2) speed of movement;

3) the path traveled by the body;

4) the position of the body in space at any time

and etc.

For example, when launching a rover to Mars, astronomers carefully calculate the position of Mars when the rover lands on the planet's surface. And for this it is necessary to calculate how the direction and modulus of the speed of Mars and the trajectory of Mars change over time.

From the course of mathematics, we know that the position of a point in space is specified using a coordinate system.

And what should we do if we have not a point, but a body? After all, each body consists of a huge number of points, each of which has its own coordinate.

When describing the movement of a body, which has dimensions, other questions arise. For example, how to describe the movement of a body, if during movement the body also rotates around its own axis. In such a case, in addition to its own coordinate, each point of a given body has its own direction of motion and its own modulus of speed.

Any of the planets can be cited as an example. When the planet rotates, opposite points on the surface have the opposite direction of motion. Moreover, the closer to the center of the planet, the lower the speed at the points.

How then to be? How to describe the movement of a body that has a size?

It turns out, in many cases, you can use the concept, which implies that the size of the body seems to disappear, but the body weight remains. This concept is called a material point.

We write down the definition:

The material point is called a body whose dimensions can be neglected under the conditions of the problem being solved.

Material points do not exist in nature. The material point is a model of the physical body. With the help of a material point, a fairly large number of tasks are solved. But it is not always possible to use the replacement of a body with a material point.

If, under the conditions of the problem being solved, the size of the body does not have a particular effect on movement, then such a replacement can be made. But if the size of the body begins to affect the movement of the body, then replacement is impossible.

There are situations in which the body can be taken as a material point:

1) If the distance that each point of the body travels is much greater than the size of the body itself.

For example, the Earth is very often considered for a material point, if its movement around the Sun is investigated. Indeed, the planet's diurnal rotation will have little effect on the annual revolution around the Sun. But if we solve the problem with diurnal rotation, then it is necessary to take into account the shape and size of the planet. For example, if you want to determine the time of sunrise or sunset.

2) With the translational movement of the body

Very often there are cases when the movement of the body is translational. This means that all points of the body move in the same direction and at the same speed.

For example, a person is climbing an escalator. Indeed, a person just stands, but each point moves in the same direction and at the same speed as the person.

A little later, we will practice identifying situations in which you can take the body for a material point, and in which not.

In addition to the material point, we need one more tool with which we can describe the movement of the body. This instrument is called a frame of reference.

Any frame of reference consists of three elements:

1) From the very definition of mechanical motion follows the first element of any frame of reference. "The movement of the body relative to other bodies." Key phrase - regarding other bodies. Those. to describe the movement we need a starting point from which we will measure the distance and generally estimate the position of the body in space. Such a body is calledreference body .

2) Again, the second element of the frame of reference follows from the definition of mechanical motion. Key phrase - over time. This means that to describe the movement, we need to determine the time of movement from the beginning at each point of the trajectory. And for the countdown we needclock .

3) And we already voiced the third element at the very beginning of the lesson. In order to set the position of the body in space, we needcoordinate system .

In this way,A reference frame is a system that consists of a reference body, a coordinate system associated with it and a clock.

Reference systems are of many types. We will consider the types of reference systems in coordinate systems.

Reference system:

Cartesian frame of reference