Presentation on the topic "Rectilinear and curvilinear motion. Movement of a body in a circle." Development of a physics lesson "Curvilinear motion" (class)

26.09.2019

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Lesson topic: Rectilinear and curvilinear motion. Movement of a body in a circle.

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Mechanical movements Rectilinear Curvilinear Motion along an ellipse Motion along a parabola Motion along a hyperbola Motion along a circle

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Lesson objectives: 1. Know the basic characteristics of curvilinear motion and the relationship between them. 2. Be able to apply the acquired knowledge when solving experimental problems.

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Topic study plan

Studying new material Conditions for rectilinear and curvilinear motion Direction of body speed during curvilinear motion Centripetal acceleration Period of revolution Frequency of revolution Centripetal force Performing frontal experimental tasks Independent work in the form of tests Summing up

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According to the type of trajectory, the movement can be: Curvilinear Rectilinear

Slide 7

Conditions for rectilinear and curvilinear motion of bodies (Experiment with a ball)

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p.67 Remember! Working with the textbook

Slide 9

Circular motion is a special case of curvilinear motion

Slide 10

Characteristics of motion – linear speed of curvilinear motion () – centripetal acceleration () – period of revolution () – frequency of revolution ()

Slide 11

Remember. The direction of particle movement coincides with the tangent to the circle

Slide 12

In curvilinear motion, the speed of the body is directed tangentially to the circle. Remember.

Slide 13

During curvilinear motion, acceleration is directed towards the center of the circle. Remember.

Slide 14

Why is acceleration directed towards the center of the circle?

Slide 15

Determination of speed - speed - period of revolution r - radius of a circle

Slide 16

When a body moves in a circle, the magnitude of the velocity vector can change or remain constant, but the direction of the velocity vector necessarily changes. Therefore, the velocity vector is a variable quantity. This means that motion in a circle always occurs with acceleration.

Remember!

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Centripetal force elastic force friction force gravitational force Model of the hydrogen atom

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1. Establish the dependence of speed on radius2. Measure the acceleration when moving in a circle3. Establish the dependence of centripetal acceleration on the number of revolutions per unit time.

Experiment

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Option 1Option 2 1. The body moves uniformly in a circle in a clockwise direction counterclockwise What is the direction of the acceleration vector during such movement? a) 1; b) 2; c) 3; d) 4. 2. The car moves with a constant absolute speed along the trajectory of the figure. At which of the indicated points on the trajectory is the centripetal acceleration minimum and maximum? 3. How many times will the centripetal acceleration change if the speed of a material point is increased or decreased by 3 times? a) will increase 9 times; b) will decrease by 9 times; c) will increase 3 times; d) will decrease by 3 times. Independent work

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Continue the sentence Today in the lesson I realized that... I liked something in the lesson that... What made me happy in the lesson... I am satisfied with my work because... I would like to recommend...

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Homework: §18-19, ex. 18 (1, 2) Additionally ex. 18 (5) Thank you for your attention. Thanks for the lesson!

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Slide captions:

Think and answer! 1. What kind of motion is called uniform? 2. What is the speed of uniform motion called? 3. What motion is called uniformly accelerated? 4. What is the acceleration of a body? 5. What is displacement? What is a trajectory?

Lesson topic: Straightforward and curvilinear movement. Movement of a body in a circle.

Mechanical motions Rectilinear Curvilinear Motion along an ellipse Motion along a parabola Motion along a hyperbola Motion along a circle

Lesson objectives: 1. Know the basic characteristics of curvilinear motion and the relationship between them. 2. Be able to apply the acquired knowledge when solving experimental problems.

Topic study plan Studying new material Conditions for rectilinear and curvilinear motion Direction of body speed during curvilinear motion Centripetal acceleration Period of revolution Frequency of revolution Centripetal force Performing frontal experimental tasks Independent work in the form of tests Summing up

According to the type of trajectory, the movement can be: Curvilinear Rectilinear

Conditions for rectilinear and curvilinear motion of bodies (Experiment with a ball)

p.67 Remember! Working with the textbook

Circular motion is a special case of curvilinear motion

Preview:

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Slide captions:

Characteristics of motion – linear speed of curvilinear motion () – centripetal acceleration () – period of revolution () – frequency of revolution ()

Remember. The direction of particle movement coincides with the tangent to the circle

In curvilinear motion, the speed of the body is directed tangentially to the circle. Remember.

During curvilinear motion, acceleration is directed towards the center of the circle. Remember.

Why is acceleration directed towards the center of the circle?

Determination of speed - speed - period of revolution r - radius of a circle

Preview:

Topic: Rectilinear and curvilinear motion. Movement of a body in a circle.

Goals: Study the features of curvilinear motion and, in particular, circular motion.

Introduce the concept of centripetal acceleration and centripetal force.

Continue work on developing key competencies of students: the ability to compare, analyze, draw conclusions from observations, generalize experimental data based on existing knowledge about body movement; develop the ability to use basic concepts, formulas and physical laws of body motion when moving in a circle.

Foster independence, teach children cooperation, cultivate respect for the opinions of others, awaken curiosity and observation.

Lesson equipment:computer, multimedia projector, screen, ball on an elastic band, ball on a string, ruler, metronome, spinning top.

Design: “We are truly free when we have retained the ability to reason for ourselves.” Cecerone.

Lesson type: lesson of learning new material.

Lesson progress:

Organizational moment:

Problem Statement: What types of movements have we studied?

(Answer: Rectilinear uniform, rectilinear uniformly accelerated.)

Lesson plan:

Update basic knowledge (physical warm-up) (5 min)

What kind of motion is called uniform?
What is the speed of uniform motion called?
What kind of motion is called uniformly accelerated?
What is the acceleration of a body?
What is movement? What is a trajectory?

Main part. Learning new material. (11 min)

Statement of the problem:

Assignment to students:Let's consider the rotation of a spinning top, the rotation of a ball on a string (demonstration of experience). How can you characterize their movements? What do their movements have in common?

Teacher: This means that our task in today’s lesson is to introduce the concept of rectilinear and curvilinear motion. Body movements in a circle.

(record the topic of the lesson in notebooks).

Lesson topic.

Slide number 2.

Teacher: To set goals, I suggest analyzing the mechanical movement pattern.(types of movement, scientific character)

Slide number 3.

What goals will we set for our topic?

Slide number 4.

I suggest studying this topic as follows plan (Select main)

Do you agree?

Slide number 5.

Take a look at the picture. Consider examples of the types of trajectories found in nature and technology.

Slide number 6.

The action of a force on a body in some cases can only lead to a change in the magnitude of the velocity vector of this body, and in others - to a change in the direction of the velocity. Let's show this experimentally.

(Conducting experiments with a ball on an elastic band)

Slide number 7

Draw a conclusion What determines the type of movement trajectory?

(Answer)

Now let's compare this definition with the one given in your textbook on page 67

Slide number 8.

Let's look at the drawing. How can curvilinear motion be related to circular motion?

(Answer)

That is, a curved line can be rearranged in the form of a set of circular arcs of different diameters.

Let's conclude:...

(Write in notebook)

Slide number 9.

Let's consider what physical quantities characterize motion in a circle.

Slide number 10.

Consider the example of a car moving. What flies out from under the wheels? How does it move? How are the particles directed? How do you protect yourself from these particles?

(Answer)

Let's conclude : ...(about the nature of the movement of particles)

Slide number 11

Let's look at the direction of speed when a body moves in a circle. (Animation with a horse.)

Let's conclude: ...( how the speed is directed.)

Slide number 12.

Let's find out how the acceleration is directed during curvilinear motion, which appears here due to the fact that the speed changes in direction.

(Animation with a motorcyclist.)

Let's conclude: ...( what is the direction of acceleration?)

Let's write it down formula in a notebook.

Slide number 13.

Look at the drawing. Now we will find out why the acceleration is directed towards the center of the circle.

(teacher explanation)

Slide number 14.

What conclusions can be drawn about the direction of velocity and acceleration?

There are other characteristics of curvilinear motion. These include the period and frequency of rotation of the body in a circle. Speed and period are related by a relationship that we will establish mathematically:

(The teacher writes on the board, students write in their notebooks)

It is known, and the way, then.

Since then

Slide number 15.

What general conclusion can be drawn about the nature of circular motion?

(Answer)

Slide number 16. ,

According to Newton's II law, acceleration is always co-directed with the force that produces it. This is also true for centripetal acceleration.

Let's conclude : How is the force directed at each point of the trajectory?

(answer)

This force is called centripetal.

Let's write it down formula in a notebook.

(The teacher writes on the board, students write in their notebooks)

Centripetal force is created by all the forces of nature.

Give examples of the action of centripetal forces by their nature:

elastic force (stone on a rope);
gravitational force (planets around the sun);
friction force (turning motion).

Slide number 17.

To consolidate this, I suggest conducting an experiment. To do this, we will create three groups.

Group I will establish the dependence of speed on the radius of the circle.

Group II will measure acceleration when moving in a circle.

Group III will establish the dependence of centripetal acceleration on the number of revolutions per unit time.

Slide number 18.

Summing up. How do speed and acceleration depend on the radius of a circle?

We will conduct testing for initial consolidation. (7 min)

Slide number 19.

Evaluate your work in class. Continue the sentences on the pieces of paper.

(Reflection. Students voice individual answers out loud.)

Slide number 20.

Homework: §18-19,

Ex. 18 (1, 2)

Additional ex. 18 (5)

(Teacher comments)

Slide number 21.

Rectilinear and curvilinear movement. Movement of a body in a circle with a constant absolute speed
Laws of interaction and motion of bodies

With the help this lesson You can independently study the topic “Rectilinear and curvilinear motion. Movement of a body in a circle with a constant absolute speed." First, we will characterize rectilinear and curvilinear motion by considering how in these types of motion the velocity vector and the force applied to the body are related. Next, we consider a special case when a body moves in a circle with a constant velocity in absolute value.

In the previous lesson we looked at issues related to the law of universal gravitation. The topic of today's lesson is closely related to this law; we will turn to the uniform motion of a body in a circle.

We said earlier that movement - This is a change in the position of a body in space relative to other bodies over time. Movement and direction of movement are also characterized by speed. The change in speed and the type of movement itself are associated with the action of force. If a force acts on a body, then the body changes its speed.

If the force is directed parallel to the movement of the body, then such movement will be straightforward(Fig. 1).

Rice. 1. Straight-line movement

Curvilinear there will be such a movement when the speed of the body and the force applied to this body are directed relative to each other at a certain angle (Fig. 2). In this case, the speed will change its direction.

Rice. 2. Curvilinear movement

So, when straight motion the velocity vector is directed in the same direction as the force applied to the body. A curvilinear movement is such a movement when the velocity vector and the force applied to the body are located at a certain angle to each other.

Let us consider a special case of curvilinear motion, when a body moves in a circle with a constant velocity in absolute value. When a body moves in a circle with constant speed, then only the direction of velocity changes. In absolute value it remains constant, but the direction of the velocity changes. This change in speed leads to the presence of acceleration in the body, which is called centripetal.

Rice. 6. Movement along a curved path

If the trajectory of a body’s movement is a curve, then it can be represented as a set of movements along circular arcs, as shown in Fig. 6.

In Fig. Figure 7 shows how the direction of the velocity vector changes. The speed during such a movement is directed tangentially to the circle along the arc of which the body moves. Thus, its direction is constantly changing. Even if the absolute speed remains constant, a change in speed leads to acceleration:

IN in this case acceleration will be directed towards the center of the circle. That's why it's called centripetal.

Why is centripetal acceleration directed towards the center?

Recall that if a body moves along a curved path, then its speed is directed tangentially. Velocity is a vector quantity. A vector has a numerical value and a direction. The speed continuously changes its direction as the body moves. That is, the difference in speeds at different moments of time will not be equal to zero (), in contrast to rectilinear uniform motion.

So, we have a change in speed over a certain period of time. The ratio to is acceleration. We come to the conclusion that, even if the speed does not change in absolute value, a body performing uniform motion in a circle has acceleration.

Where is this acceleration directed? Let's look at Fig. 3. Some body moves curvilinearly (along an arc). The speed of the body at points 1 and 2 is directed tangentially. The body moves uniformly, that is, the velocity modules are equal: , but the directions of the velocities do not coincide.

Rice. 3. Body movement in a circle

Subtract the speed from it and get the vector. To do this, you need to connect the beginnings of both vectors. In parallel, move the vector to the beginning of the vector. We build up to a triangle. The third side of the triangle will be the velocity difference vector (Fig. 4).

Rice. 4. Velocity difference vector

The vector is directed towards the circle.

Let's consider a triangle formed by the velocity vectors and the difference vector (Fig. 5).

Rice. 5. Triangle formed by velocity vectors

This triangle is isosceles (the velocity modules are equal). This means that the angles at the base are equal. Let us write down the equality for the sum of the angles of a triangle:

Let's find out where the acceleration is directed at a given point of the trajectory. To do this, we will begin to bring point 2 closer to point 1. With such unlimited diligence, the angle will tend to 0, and the angle will tend to . The angle between the velocity change vector and the velocity vector itself is . The speed is directed tangentially, and the vector of speed change is directed towards the center of the circle. This means that the acceleration is also directed towards the center of the circle. That is why this acceleration is called centripetal.

How to find centripetal acceleration?

Let's consider the trajectory along which the body moves. In this case it is a circular arc (Fig. 8).

Rice. 8. Body movement in a circle

The figure shows two triangles: a triangle formed by velocities, and a triangle formed by radii and displacement vector. If points 1 and 2 are very close, then the displacement vector will coincide with the path vector. Both triangles are isosceles with the same vertex angles. Thus, the triangles are similar. This means that the corresponding sides of the triangles are equally related:

The displacement is equal to the product of speed and time: . Substituting this formula, we can obtain the following expression for centripetal acceleration:

Angular velocity denoted by the Greek letter omega (ω), it indicates the angle through which the body rotates per unit time (Fig. 9). This is the magnitude of the arc in degree measure traversed by the body over some time.

Rice. 9. Angular velocity

Please note that if solid rotates, then angular velocity for any points on this body will be a constant value. Whether the point is located closer to the center of rotation or further away is not important, i.e. it does not depend on the radius.

The unit of measurement in this case will be either degrees per second () or radians per second (). Often the word “radian” is not written, but simply written. For example, let’s find what the angular velocity of the Earth is. The Earth makes a complete rotation in one hour, and in this case we can say that the angular velocity is equal to:

Also pay attention to the relationship between angular and linear speeds:

Linear speed is directly proportional to the radius. The larger the radius, the greater the linear speed. Thus, moving away from the center of rotation, we increase our linear speed.

It should be noted that circular motion at a constant speed is a special case of motion. However, the movement around the circle may be uneven. Speed can change not only in direction and remain the same in magnitude, but also change in value, i.e., in addition to a change in direction, there is also a change in the magnitude of velocity. In this case we are talking about the so-called accelerated motion in a circle.

What is a radian?

There are two units for measuring angles: degrees and radians. In physics, as a rule, the radian measure of angle is the main one.

Let's build central angle, which rests on an arc of length .

Lesson in 9th grade.

Subject: Rectilinear and curvilinear movement. Movement on

circles with a constant modulus speed.

Lesson objectives: 1. Give schoolchildren an idea of the curvilinear

movement, period, frequency; idea of direction and

value of speed and acceleration when moving along

circles.

2. Continue to develop the ability to apply

theoretical knowledge for solving practical problems;

promote the development of the ability to compare,

analyze.

3. Instill in students an interest in science and the subject of physics.

Equipment:For the teacher– slides “Curvilinear and rectilinear

movement", "Circular movement", tripod with ball

on a thread, a tripod with a fixed groove, a magnet,

crossword.

For students– a tripod with a ball attached to a thread,

clock with second hand, sheets with test tasks,

cards.

Board design: the topic of the lesson is written on the board, the crossword puzzle grid is drawn, tasks for independent solution are written, the student prepares a drawing for the answer, written down homework.

Lesson plan.

I. Organizational moment
II. Updating the acquired knowledge.
III. Explanation of new material.
IV. Fixing the material.
V. Knowledge control.
VI. Homework.
VII. Summing up the lesson.

Lesson progress

1.Organizational moment.

TEACHER: Hello! I am glad to welcome you to the physics lesson.

The great French physicist Pascal said: “... our knowledge can never have an end precisely because the subject of knowledge is infinite.”

Today in class we will try to make a little progress in our knowledge of the world around us.

Let's remember what we already studied in 9th grade.

STUDENT: We studied rectilinear uniform and rectilinear uniformly accelerated motion.

TEACHER: Is it just straight motion found in the world around us?

STUDENT: No. Straight-line movement is rare. More often, bodies move not in a straight line, but along a curved line.

TEACHER: So, what is the task before us, what should we do in class today?

STUDENT: We will study curvilinear motion.

TEACHER: What does it mean to “study movement”?

STUDENT: To study movement means to introduce some of its characteristics.

TEACHER: Right! That is, today in the lesson we will look at the features of curvilinear movement, introduce new characteristics of movement and, as an example of curvilinear movement, consider movement in a circle.

2. . Updating the acquired knowledge.

TEACHER: But before moving on to a new topic, let us remember what we know about motion, about basic physical quantities and concepts. Let's do a physical warm-up and solve a crossword puzzle (The crossword puzzle grid is drawn on a piece of Whatman paper. The student enters the correct answer into the crossword puzzle grid, students are asked additional questions. Type of work - whole class, individual).

1. Physical vector quantity,

measured in meters.

(move)

1a. What is movement?

1b. What are the units of movement?

You know?

2. Unit of measurement of angle.

2a. What device is used to measure angles?

3. A physical quantity, the units of measurement of which are century, year.

3a. Name the SI unit of time.

3b. What instruments are used to measure time?

4. A physical quantity showing the speed of speed measurement.

(acceleration)

4a. What is acceleration?

4b. In what units is acceleration measured?

5. Path length.

5a. Imagine that you ran one lap around the stadium. What is greater - the path or the movement?

5b. When is path equal to displacement?

6. Physical vector quantity characterizing the speed of movement.

(speed)

6a. What units of speed do you know?

6b. What device measures speed?

7. One of the main units of measurement in physics.

7a. name the SI base units.

7b. What physical quantities correspond to them?

8. Change in body position in space over time.

(movement)

8a. Name the types of motion depending on acceleration.

8b. What kind of motion is called uniform? Uniformly accelerated?

While the class is working on the crossword puzzle, 5 students (strong) complete the task on the spot using cards.

3. Explanation of new material.

TEACHER: We solved the crossword puzzle. The word that will be key in the study is highlighted vertically. new topic"Curvilinear movement." What is this word?

STUDENT: Trajectory.

TEACHER: Let's remember what a trajectory is?

STUDENT: A trajectory is a line along which a body moves.

TEACHER: Do movements differ according to the type of trajectory? Let's look at examples of movement.

Demonstration: 1) a plasticine ball falling vertically down; 2) rolling the ball along the chute; 3) rotation of the ball on the thread; 4) rolling the ball along a chute next to the magnet.

TEACHER: How can observed movements be classified?

STUDENT: the falling and rolling of the ball is a rectilinear movement, and the rotation and rolling next to the magnet is a curvilinear movement.

TEACHER: Remember the definition of rectilinear motion and, by analogy, try to give a definition of curvilinear motion. Write it down in your notebook (Write it down yourself, then read it out).

STUDENT: Curvilinear movement is movement whose trajectory is a curved line.

TEACHER: Give examples of linear and curved motion.

STUDENTS: (suggested answers) rectilinear: a pencil falling from a desk, a tram moving without turning; curvilinear: planetary movement, car turning

TEACHER: Now let’s introduce the characteristics of curvilinear motion, thinking about what quantities to describe it. Consider two trajectories of curvilinear motion. Think about how to describe the first type of movement?

STUDENT: In the first case, the trajectory can be divided into rectilinear sections, as we know how to describe rectilinear motion.

TEACHER: Right! And in the second case, what proposals will there be? How to describe the second type of movement?

STUDENT: The trajectory can be divided into circular arcs.

TEACHER: Do this in your notebook using compasses (students complete the construction independently). That is, curvilinear movement can be represented as movement in a circle. Consider the motion of a body in a circle. This is the simplest and most common type of curvilinear movement.

Demonstration of a slide of movement in a circle.

TEACHER: Give more examples of the motion of bodies in a circle.

STUDENT: Movement of planets, clock hands.

TEACHER: Well done! To characterize the movement, you need to introduce some quantities. Think about what is special about moving in a circle?

STUDENT: This movement is repeated.

TEACHER: Let's write down the characteristics of motion in a circle.

First characteristic:

Period T is the time of one full revolution.

TEACHER: What is it measured in?

STUDENT: Since this is time, it is measured in seconds.

TEACHER: If during time t the body makes N revolutions, how to find the period?

STUDENT: Need to total time divide by the number of revolutions.

TEACHER: Right! Let's write the formula:

TEACHER: Now let’s hear a message about the period (the message was prepared by the student in advance).

Message 1. Period is a quantity that is found quite often in nature, science and technology. So, we know that the Earth rotates around its axis and the average period of this rotation is 24 hours; a complete revolution of the Earth around the Sun occurs in approximately 365.26 days; the impellers of hydraulic turbines make one full revolution in 1 s, and the propeller of a medium or light helicopter has a rotation period from 0.15 to 0.3 s; The period of blood circulation in humans is approximately 21-22 s.

TEACHER: Give more examples of rotation periods of bodies known to you (write 1-2 examples in your notebook yourself).

So, the period of rotation of the Earth and the Moon, what are they equal to?

STUDENT: Rotation period

The Earth is 365 s, and the Moon is 30 s.

TEACHER: Who spins faster?

STUDENT: The Moon rotates faster.

TEACHER: So what is the second characteristic of movement?

STUDENT: Speed of rotation.

TEACHER: Right! Or frequency. Frequency () is the number of revolutions per unit of time.

Unit of measurement:  = s -1.

If during time t the body makes N revolutions, then the rotation frequency  = .

Look carefully at the formulas for period and frequency that we wrote down, what conclusion can be drawn about the relationship between the period and frequency values?

STUDENT: Period and frequency are mutual reciprocals, the period is inversely proportional to the frequency, and the frequency is inversely proportional to the period.

TEACHER: Write down this dependence yourself in your notebook.

What is frequency and why is it interesting? Let's hear a message (prepared in advance by the student).

Message 2. To measure frequency, there are special instruments - the so-called circles for measuring frequency, the action of which is based on optical illusion. On each such circle there are black stripes and the frequency value is indicated. When rotating, the black stripes form a circle of a certain thickness at the corresponding frequency. Tachometers are also used to measure frequency. Here is some information about the speed of rotation of technical devices: crankshafts of tractor engines have a speed of rotation from 60 to 100 1/s, the rotor of a gas turbine rotates with a frequency of 200 to 300 1/s; a bullet fired from a Kalashnikov assault rifle rotates with a frequency of 3000 1/s.

TEACHER: How else do we characterize any movement?

STUDENT: Any movement is characterized by speed.

TEACHER: Let's think about the direction of speed when moving in a circle? Let's remember: a car is slipping, where does the dirt fly out from under the wheels? Introduced?

Now open the textbook page 69 figure 38 ( independent work with a textbook). What can be concluded from these examples?

STUDENT: The speed when moving in a circle is directed tangentially.

ACCOUNTANT: Write this down in your notebook and sketch the direction of speed when moving in a circle

Now look at the drawing. What can you say about the direction of speed? Is it changing?

STUDENT: Yes, the direction of speed changes.

TEACHER: Can we say that the speed changes?

STUDENT: Yes. The speed changes.

TEACHER: Why do we say this? Remember what the speed is? Vector or scalar?

STUDENT: Speed is a vector quantity, i.e. both value and direction are important for it. And if the direction changes, then the speed itself changes.

TEACHER: So, what kind of motion is it in a circle: uniform or uniformly accelerated?

STUDENT: This is an accelerated movement.

TEACHER: Write this conclusion in your notebook (by yourself).

So, what is the fourth characteristic of curvilinear motion?

STUDENT: This is acceleration.

TEACHER: Let's find out what the acceleration is equal to and where it is directed when moving in a circle.

Let us determine the direction of the acceleration of a body if it moves in a circle with a constant velocity in absolute value. To do this, let's look at the figure. It shows a body ( material point), moving in a circle of radius r. In a very short period of time t, this body moves from point A to point B, which is located very close to point A. In this case, the difference in the length of the arc AB and the chord
can be neglected and assume that the body moves along a chord. But the directions of the velocities v 0 and v that the body had at points A and B, respectively, are still different. The acceleration of a body is determined by the formula:

The acceleration vector is codirectional with a vector equal to the geometric speed difference (v – v 0). To find this vector, move the vector parallel to itself at point A and connect the ends of the velocity vectors with a straight line segment directed from To . This will be the vector (v – v 0). We see that it is directed inside the circle.

As the time interval t approaches zero, the segment AB contracts to a point. The acceleration vector is directed towards the center of the circle. Therefore, the acceleration with which a body moves in a circle with a constant absolute speed is called centripetal. Centripetal acceleration at any point is directed along the radius of the circle towards its center.

TEACHER: Write down in your notebook where the acceleration is directed when moving in a circle. Fine.

Considering the similarity of triangles, we get

The following students will prepare the derivation of this formula for the next lesson. . . (the task is given to students with high level knowledge).

4. Consolidation.

TEACHER: So, what did we learn about curvilinear motion today? Remember, look at your notes.

Now let’s check whether you have understood today’s topic well. You need to solve an experimental problem. We work in groups of 4 (students have a tripod with a ball on a string on their tables).

TASK 1: Determine the period of revolution of the ball.

TASK 2 (for students with a high level of knowledge). Explore what determines the period of rotation?

Then we discuss the results and find out that the rotation period depends on the rotation speed and radius.

TEACHER: Now let’s digress a little and combine physics and lyrics.

(There are 2 problems on the screen. Solve them independently, then check each other).

1 – option.

Task 1. A.S. Pushkin "Ruslan and Lyudmila"

At Lukomorye green oak,

Golden chain on the oak tree;

Day and night the cat is a scientist

Everything goes around and around in a chain. . .

What is this cat movement called? Determine the frequency of his movement if in 1 minute he makes 6 “circles” (revolutions). What is the period?

ANSWERS:  = 0.1 s -1, T = 10 s.

2 – option.

Problem 2. A.M. Gorky "Makar Chudra"

And they both (Loiko Zobar and Rada. - A.S.) circled in the darkness of the night smoothly and silently, and the handsome Loiko could not catch up with the proud Rada.

Determine the hero's circulation period if his circulation frequency is 2 s -1.

ANSWER: T = 0.5 s.

(brief discussion of tasks).

TEACHER: It's time to check how you've learned new material. So, there are tests on the table in front of you. Tests at different levels: initial, intermediate, sufficient levels. Write your name on pieces of paper and start working. The test takes 5 minutes to complete.

After completing the test, the correct answers are revealed. The guys evaluate themselves (self-control).

Evaluation criteria:

Sufficient level: “5” - 5

Average level: “4” - 4-5

Entry level: “3” - 4-5

(Students hand in sheets with grades).

5. Homework.

Write in the diary: § 18, 19 (answer according to a generalized plan)

“5” - Ex. 17(3) orally, Ex. 18(4) in writing.

“4” - Ex. 17(2) orally, Ex. 18(1) in writing.

6. Summing up the lesson.

TEACHER: So, what did we study today, what did we learn new?

The concept of curvilinear motion was introduced.

Its characteristics were introduced: period, frequency, speed, acceleration.

Let's remember what period and frequency are; where is the speed directed when moving in a circle; where is the acceleration directed and what is it equal to?

TEACHER: Well done! Well, who can be rewarded with an assessment?

Students evaluate the work of their classmates (peer assessment).

Evaluated:

Working with a crossword puzzle (individual students).

Students' answers from their seats during the explanation.

Answers from students who prepared the message.

Answer from a student explaining a new topic.

In addition, all students received marks for completing the test and 5 students will receive marks for working on the cards.

TEACHER: Thanks for the lesson. Goodbye.

TASKS ON THE CARDS

Describe the motion of a body whose velocity projection graph is shown in the figure.

The equation of body motion is s = 2t + t 2. Describe this movement (indicate the values of the quantities characterizing it), construct a graph of s x (t).

The time dependence of the coordinates of a point moving along the x axis has the form: x = 2 - 10t + 3t 2. Describe the nature of the movement. What are the initial velocity and acceleration? Write down the equation for the velocity projection.

A freight train leaving the station was traveling at a speed of 36 km/h. After 0.5 hours, a fast train departed in the same direction, the speed of which was 72 km/h. How long after the freight train leaves will the fast train catch up with it?

A skier covered a slope 100 m long in 20 s, moving with an acceleration of 0.3 m/s 2 . What is the speed of the skier at the beginning and end of the slope?

Answers to tests

Entry level

B-1. B-2.

Intermediate level

B-1. B-2.

Sufficient level