2020 high school physics circular motion teaching plan daquan 1.
circular motion
First, the requirements of the syllabus.
1. Master the physical quantities describing circular motion and their relationships.
2. Understand and apply the centripetal force formula; Understand the conditions for objects to do centrifugal motion.
Second, knowledge combing
1. describes the physical quantity of circular motion.
(1) linear velocity: a physical quantity describing the circular motion speed of an object.
v= =。
(2) Angular velocity: a physical quantity describing the rotation speed of an object around the center of a circle.
ω= = .
(3) Period and frequency: physical quantities describing the rotation speed of an object around the center of a circle.
T=，T=。
(4) centripetal acceleration: a physical quantity that describes the change of speed.
an=rω2= =ωv= r。
2. Centripetal force
(1) Effect: centripetal acceleration is generated, only the direction of speed is changed, but the speed is not changed.
(2) size: F=m =mω2r=m =mωv=4π2mf2r.
(3) Direction: always pointing to the center of the circle along the radial direction, always changing, that is, the centripetal force is a variable force.
(4) Source: The centripetal force can be provided by one force, or by the resultant force of several forces or the component of one force.
3. Uniform circular motion and non-uniform circular motion
(1) moves in a uniform circle.
① Definition: Circular motion with constant linear velocity.
② Properties: The size of centripetal acceleration is constant, and the direction always points to the center of the circle.
(3) The condition of uniform circular motion of particles.
The resultant force is constant, and the direction is always perpendicular to the speed direction, pointing to the center of the circle.
(2) Non-uniform circular motion
① Definition: Circular motion with linear velocity and direction change.
② the function of resultant force
A. The component Ft of the resultant force along the speed direction produces tangential acceleration, Ft=mat, which only changes the speed direction.
The radial component Fn of the resultant force B produces centripetal acceleration, Fn=man, and only changes the speed.
4. Centrifugal movement
(1) Essence: An object that moves in a circle always cuts along the circle due to its own inertia.
The tendency to fly in a straight line.
(2) Stress characteristics (as shown)
① When F=mrω2, the object moves in a uniform circle;
(2) When F=0, the object flies out in the tangential direction;
3 when F.
Provide centripetal force for practice.
④ when f >; When mrω2, the object gradually approaches the center of the circle and makes centripetal motion.
Third, the main point of view analysis
1. Relationship between physical quantities of circular motion
2. Understanding of Formulas v=ωr and a= =ω2r
(1) from v=ωr, when r is constant, v is proportional to ω; When ω is constant, V is proportional to R; When v is constant, ω is inversely proportional to R.
(2) From a= =ω2r, we can know that when V is constant, A is inversely proportional to R; When ω is constant, A is proportional to R. 。
3. Three common transmission modes and characteristics
(1) belt drive: As shown in Figures A and B, when there is no relative sliding between the belt and the two wheels, the edge line speed of the two wheels is equal, that is, vA=vB.
(2) Friction transmission: As shown in Figure A, when the edges of two wheels are in contact and there is no slip at the contact point, the speeds of the two wheel edges are equal, that is, vA=vB.
(3) Coaxial transmission: As shown in Figure B, two wheels are fixed together and rotate around the same axis, and the angular velocities of the two wheels are equal, that is, ω a = ω b. 。
4. The source of centripetal force
The centripetal force is named according to the function of force, which can be various forces such as gravity, elasticity and friction, or the resultant force of several forces or the component of a certain force, so it is necessary to avoid adding another centripetal force in the force analysis.
5. Determination of centripetal force
(1) First, determine the position of the plane and the center of the circle.
(2) Through the analysis of the force on the object, it is found that the resultant force of all forces pointing to the center of the circle along the radius direction is the centripetal force.
6. Key problems in circular motion
Critical problems widely exist in middle school physics. The key to solve the critical problem is to judge the critical state accurately, and then choose the corresponding law to solve it flexibly. The steps to solve the problem are as follows:
(1) judging the critical state: the words "just right", "just right" and "just right" appear in some topics, which obviously indicates that there is a critical point in the description of the topic; If there are words such as "value range", "how long" and "how far" in the title, it means that there are "starting points and ending points" in the description of the title, and these starting points and ending points are often crucial; If the words "maximum", "minimum", "maximum" and "at least" appear in the title, it means that there is an extreme value in the title description process, and this extreme point is often a critical state.
(2) Determination of critical conditions: After judging that there is a critical state in the process described in the topic, the conditions under which the critical state appears should be clarified through analysis and expressed in mathematical form.
(3) Selection of physical laws: When the critical state and critical conditions of the motion of an object are determined, the corresponding physical laws should be selected for different motion processes or phenomena, and then the equations are solved.
7. "Light rope, light rod" that moves circularly in the vertical plane
[Model Overview]
When an object moves in a circle in a vertical plane, when it moves to the highest point of its trajectory, the forces acting on it can be divided into two types. One is unsupported (such as the connection between the ball and the rope, the roller coaster along the inner rail, etc.) ), called "light rope mode"; Second, there is support (such as the connection between the ball and the rod, the movement of the ball at the elbow, etc.). ), the so-called "polished rod model".
[Model conditions]
(1) The object moves in a circular motion with variable speed in the vertical plane.
(2) The "light rope model" has no support at the highest point of the track, and the "light pole model" has support at the highest point of the track.
[Model characteristics]
Such problems often have key problems, accompanied by words such as "maximum", "minimum" and "just right". The analysis and comparison of the two models are as follows:
? The common type of rope mould rod mould is support ball. The critical condition for passing the highest point is from mg=m to V Pro = V Pro =0. It is discussed and analyzed that when (1) passes through the highest point, v≥, FN+mg=m, rope and circular track exert elastic force on the ball. When FN(2) can't pass the highest point, V F is, and the object makes centrifugal motion; If f needs it
(1) In order to ensure that the ball can make a complete circular motion in the vertical plane, at least how much horizontal velocity should be applied to the ball at point A?
(2) How many Zhang Liwei are there in the rope when the ball is thrown horizontally at the speed of v 1=4 m/s?
(3) At the moment when the ball is thrown horizontally at the speed of v2= 1 m/s, if the rope has tension, find its size; If there is no tension, try to find out how long it takes for the rope to straighten again.
The answer (1)? M/s (2)3 N (3) no tension, 0.6 s
The critical condition for analyzing (1) the circular motion of a ball is the centripetal force of the ball when gravity just provides the highest point, that is, mg=m=, and the solution is v0 = = m/s. 。
② because of v1>; V0, so the rope has tension. According to Newton's second law, there is FT+mg=m, and the rope tension substituted into the data is ft = 3 n.
(3) Because v2
10. On the expressway paved with high-grade asphalt, the design speed of the car is 108 km/h, and the maximum static friction between the tire and the ground is equal to 0.6 times the weight of the car when driving on this road.
(1) If a car turns on a horizontal curve of this expressway, assuming that the road surface of the curve is horizontal, what is the minimum radius of the curve?
(2) If a circular arch overpass is designed on the expressway, what is the radius of the circular arch overpass at least, so that cars can safely pass through the circular arch bridge at the designed speed? (take g g= 10/0m/s2)
Answer (1)150m (2) 90m.
Analysis (1) When a car turns on a horizontal road, it can be regarded as uniform circular motion, and its centripetal force is provided by the static friction between the car and the road. When the static friction reaches the maximum, the centripetal force formula shows the smallest radius, Fmax=0.6mg=m, which is obtained from the speed v =108 km/h = 30 m/s.
(2) When the car passes through the arch bridge, it can be regarded as doing uniform circular motion in the vertical plane. When it reaches the highest point, it is mg-FN=m according to the centripetal force formula. In order to ensure safe passage, the elastic force FN between the car and the road surface must be greater than or equal to zero. If there is mg≥m, R ≥ 90 m. 。
1 1. There are eight hanging baskets symmetrically distributed on the small "Ferris wheel" in the amusement park, and a classmate with a mass of m stands in each hanging basket. As shown in the figure, the "Ferris wheel" rotates counterclockwise in the vertical plane at a uniform speed. If a classmate who turns to vertex A at a certain moment lets a small heavy object fall freely, he immediately informs the students below to catch it. As a result, just when the heavy object begins to fall, classmate B in C is the first.
(1) Time t before catching a heavy object.
(2) The linear velocity of people and hanging baskets moving with the Ferris wheel, v 。
(3) The pressure of student B on the hanging basket at the lowest point FN.
Answer (1)2
(2)
(3)( 1+) mg; Vertical downward
Analytic (1) is derived from kinematic formula: 2R= gt2, t=2.
2020 senior high school physics circular motion teaching plan daquan II
Teaching objectives
Knowledge and skills
1, knowing that if the function of a force or the resultant force of several forces is to make an object produce centripetal acceleration, it is the centripetal force of the object doing circular motion. Will analyze the source of centripetal force in specific problems.
2. Understand the law of uniform circular motion.
3. Knowing that the formulas of centripetal force and centripetal acceleration are also applicable to variable-speed circular motion, we can find out the centripetal force and centripetal acceleration of an object at a special point in variable-speed circular motion.
Process and method
1. Through the example analysis of uniform circular motion, the theory is integrated with practice to improve students' ability to analyze and solve problems.
2. The law of uniform circular motion can also be used for variable-speed circular motion, which permeates the dialectical relationship between particularity and generality and improves students' analytical ability.
Emotions, attitudes and values
The analysis of several examples makes students clear that specific problems must be analyzed in detail and learn to deal with problems reasonably and scientifically.
★ Teaching emphasis: centripetal force can be found in specific problems, and related problems can be solved by combining Newton's laws of motion.
★ Teaching difficulty 1, the source of centripetal force in specific problems. 2. Discussion and analysis of key issues.
Students who study situation analysis have mastered the general methods to solve the problem of circular motion through the study in the last class. On this basis, this lesson deeply discusses the circular motion in life, especially the solution of key problems.
When discussing these examples in the textbook, teaching material analysis should grasp such a basic idea, that is, first analyze the force on the object, and then list the equations to solve.
Teaching means and facilities inquiry teaching. A transparent plastic bottle and a roller coaster demonstrator.
teaching process
Reviewing the past helps to understand the present.
1. Mechanical properties of objects with uniform circular motion: combined external forces provide centripetal force.
2. review of centripetal force formula: Fn=man=m =mr =mr( )2
3. Overview of automobile crossing the bridge;
The resultant force in the vertical direction provides the perimeter.
Centripetal force required for exercise
mg-FN=m mg-FN=m
Class introduction: Show students the pictures of roller coaster and demonstrate the performance of water meteor, and ask: Why didn't the roller coaster fall at the highest point? What should I do if the water stops running? To solve this mystery, let's go into this section-circular motion in a vertical plane.
Classroom autonomous learning
Rope model
The ball tied by the rope moves in a circle in the vertical plane.
Demonstrate using a rope to tie a heavy object and do circular motion on the vertical plane.
Problem discussion
(1) Analyze the relationship between the force and motion of the ball at the lowest point.
(2) Analyze the situation of the ball at the highest point.
Specific steps: guide students to follow the steps.
Force analysis of 1. ball. 2. Column type
3. According to the formula, when the speed decreases, what changes with it and how?
Gossip about sb.' s mistakes
1. When the ball just passes the highest point, it should encounter a pulling force _ _. At this time, the speed of the ball passing through the highest point is the smallest, which is usually called critical speed V0. At this time _ _, provide centripetal force, with _ _ _ _ _ _, V0=___.
2. If the ball speed is less than V0 at the highest point, the ball will fall under the action of _ _ gravity.
(mg>m, the ball moves near the heart)
3, if the ball speed is greater than V0 at the highest point, the ball moves in a circle under the action of _ _ _. At this time, the centripetal force is provided by _ _ _ _ * *. Format: _ _ _ _ _ _.
(2) The ball moves in a circle on the inner side of the vertical smooth track surface. (roller coaster model)
(Students analyze and discuss the answers)
What is the source of centripetal force of the ball at the highest point?
Line: _ _ _ _ _ _ _ _
What is the source of centripetal force at the lowest point?
Line: _ _ _ _ _ _ _ _
3. When the ball just passes the highest point, it is necessary to satisfy the elastic force and the critical speed v0 of the formula _ _ _ = _ _.
If the speed of the ball at the highest point is less than V0, the ball will fall under the action of _ _ gravity.
5. If the speed of the ball at the highest point is greater than V0, the ball will make a circular motion under the action of _ _ _. At this time, the centripetal force is provided by _ _ _ _ * *. The formula is _ _ _ _.
(3) Water meteor model. (autonomous learning)
2020 senior high school physics circular motion teaching plan daquan 3
I. teaching material analysis
"Uniform circular motion" is the fourth section of chapter 5 of physics compulsory course 2 in senior high school. It is another beautiful curve movement that students come into contact with after fully mastering the law of curve movement and the handling methods of curve movement problems. As an important part of this chapter, this section mainly introduces several basic concepts describing circular motion to students, laying a good foundation for subsequent study.
One of the characteristics of the textbook of People's Education Edition is to let students get perceptual knowledge based on experimental facts, and then summarize the laws through theoretical analysis, thus forming rational knowledge.
After enumerating some circular motion scenes in life, the textbook puts forward the problem of describing the circular motion speed by observing the relative rotation of the big gear, the small gear and the rear wheel of the bicycle.
Second, the teaching objectives
1. Knowledge and skills
① Know what circular motion is and what uniform circular motion is. Understand the concept of linear velocity; Understand the concepts of angular velocity and period, and use their formulas to calculate.
② Understand the relationship among linear velocity, angular velocity and period: v = rω = 2π r/t.
③ Understand that uniform circular motion is variable-speed motion.
④ We can use the related formula of uniform circular motion to analyze and solve problems in specific situations.
2. Process and method
① Use extreme thinking to understand the instantaneity and vector of linear velocity, and master the characteristics of circular motion to analyze related problems.
② Understand why angular velocity should be introduced after linear velocity, and use mathematical knowledge to deduce the unit of angular velocity.
3. Emotions, attitudes and values
(1) Through the application of extreme thinking and mathematical knowledge, we can understand the relationship between subject knowledge and establish the viewpoint of universal connection.
② Experience the fun of applying knowledge, feel that physics is around, and stimulate students' interest in learning.
(3) Education of love. In the communication with students, express love and appreciation, such as smiling and saying "good!" " ""you are great! " "Analysis of the right! "Let students get affirmation and encouragement, and study happily.
Third, the focus and difficulty of teaching
1. Focus
① Understand the concepts and introduction process of linear velocity, angular velocity and period;
(2) Grasp the connection between them.
2. Difficulties
① Understand the physical meaning of linear velocity and angular velocity and the necessity of introducing concepts;
② Understand that uniform circular motion is variable-speed motion.
Fourthly, the analysis of learning situation.
Students' existing knowledge:
1. The concept of instantaneous velocity
2. Preliminary limit thought
3. Habits of thinking and discussion
4. Expression of angle in math class
Teaching methods and means of verbs (abbreviation of verb)
Demonstrate experiments, show pictures, watch videos and animations;
Discuss, teach, reason and summarize.
Teacher-student interaction, student interaction,
Teaching design of intransitive verbs
(A) the introduction of new lessons (understanding circular motion)
Let students know the characteristics of circular motion by demonstrating experiments, showing pictures, watching videos and animations.
Demonstrate the circular motion of the ball on the horizontal plane.
Show pictures of bicycles, clocks, electric fans, etc.
Watch the animation of the earth moving around the sun.
Watch figure skating video
Question: What are the similarities between their actions? A: Their trajectory is a circle.
Yes, this is the circular motion we are going to learn today.
Look at the animation and think: What's the difference between these two balls doing uniform circular motion? A: The speed is different.
Ask a question: how to describe the speed at which an object moves in a circle?
Students practice in groups, observe the transmission of bicycles, think and discuss;
The particles in the big gear, the small gear and the rear wheel of the bicycle are all moving in a circle.
Compare which point moves faster? Tell me the reason for your comparison.
After the discussion, show pictures (or videos) of bicycle transmission, and ask further questions: How to compare the speed of circular motion of objects? Teachers and students * * * analyze and summarize possible comparison methods:
Scheme 1: Compare the length of the arc that an object passes through in a period of time.
Scheme 2: Compare the rotation angles of the radius of the object within a period of time.
Option 3: Compare the time of one revolution of the object.
Scheme 4: Compare the number of rotations of an object in a period of time.
Note: express encouragement and appreciation when communicating with students, such as "very good!" "You are great!" "That's right!" Wait a minute.
(B) the new curriculum teaching
A physical quantity describing the speed of circular motion
linear velocity
Read the text, think and discuss the following questions:
1. What is the definition of linear velocity? What is the unit?
2. What is the direction of linear velocity? Please tell me how to determine the speed direction of circular motion.
3. What are the characteristics of the linear velocity of an object in uniform circular motion?
4. Why is uniform circular motion variable? What does "uniform speed" mean here?
Student-student interaction, after teacher-student interaction, can be summarized as follows: click on the slide to learn and summarize the concept of linear velocity in all directions; And through the video of grinding wheel cutting, let students feel the speed direction of circular motion. As follows:
Linear speed:
Definition: The ratio of arc length Δ l and time Δ t through which a particle moves in a circle is called linear velocity.
Size: v = Δ l/Δ t (Analysis: When Δ t is small, v is the instantaneous speed of each point on the circumference. )
Unit: m/s direction: along the tangent direction of this point on the circumference (see grinding wheel working video).
Physical meaning: Describe the speed of arc length.
Uniform circular motion: the particle moves along the circle, and the linear velocity is equal everywhere. This kind of motion is called uniform circular motion.
Watch the animation and learn the concept of uniform circular motion: particles move along a circle, and the linear velocity is equal everywhere. This kind of motion is called uniform circular motion. Ask students to give more examples of circular motion in their lives. )
Discussion on uniform circular motion;
1. Is the linear velocity of uniform circular motion constant? Does "uniform speed" here mean uniform speed?
2. Is uniform circular motion uniform?
Note: express encouragement and appreciation when communicating with students, such as "great!" "You are amazing!" Wait a minute.
After discussion, it is summarized as follows:
Uniform circular motion is variable speed motion! (The direction of linear velocity is changing all the time)
"Uniform speed" means uniform speed.
Uniform circular motion is a motion with constant linear velocity!
angular velocity
Look at the picture and answer the question: (steering angular velocity learning)
Observe the transmission of bicycle and analyze which point moves faster, P and N, M and N? Which point turns faster? Please discuss it!
Through discussion, the students found that the fast motion and fast rotation of particles are not the same thing! It is necessary to introduce a physical quantity ── angular velocity (in angular velocity learning) to represent rotational speed.
Note: express encouragement and appreciation when communicating with students, such as "Good analysis!" "Not bad!" Wait a minute.
Next, we study the physical quantity describing the rotation speed of uniform circular motion-angular velocity.
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