Teaching objectives of "mechanical energy and its transformation" in the second volume of 8th grade Physics published by People's Education Press.
1. Knowledge and skills
(1) It is known that mechanical energy includes kinetic energy and potential energy. The mutual transformation between kinetic energy and potential energy can be understood by examples.
(2) It can explain some simple phenomena of mutual transformation of kinetic energy, gravitational potential energy and elastic potential energy.
(3) Understand the meaning of conservation of mechanical energy.
2. Process and method
Through observation and experiment, we can understand the transformation process of kinetic energy and potential energy.
3. Emotions, attitudes and values
(1) Pay attention to the relationship between mechanical energy and people's lives, and have the consciousness of applying mechanical energy to life.
(2) Cultivate students' patriotism.
Emphasis and difficulty in teaching
The transformation process of kinetic energy and potential energy.
teaching tool
Rolling pendulum, iron lock, string, yo-yo, iron frame, steel ball, fine iron wire, inclined plane with spring.
teaching process
Introduce a new lesson:
First, check the import.
We have learned about energy transformation in the second day of junior high school. Please answer, how is the energy converted when the electric lamp works? How is the energy converted when the wind turbine works? How is the energy converted when the hydraulic engine works? How is the energy converted when the motor works?
Students discuss and answer.
Second, the situation: operate table tennis to attract students' attention and go straight to the subject.
Use your hands and brain to explore:
1. The teacher asked: Why can table tennis keep moving up and down after it is released? This requires students to explore:
Experiment 1: roll pendulum experiment: show the roll pendulum and briefly introduce the structure and experimental method of the roll pendulum. Draw a bright color sign on the side of the balance wheel in advance, tell the students to observe the color sign and judge the rotating speed of the balance wheel.
2. Student experiment
Put the roller to the highest point first, and then loosen the balance wheel. Analysis: the balance wheel is at rest at the highest point, at which time the balance wheel has only gravitational potential energy and no kinetic energy. When the balance wheel descends, its height decreases and its gravitational potential energy decreases. The balance wheel rotates and descends; The faster it rotates, the greater its kinetic energy. When the pendulum turns to the lowest point, it rotates fastest and has the largest kinetic energy; It has the lowest height and the smallest gravitational potential energy. During the descent of the balance wheel, its gravitational potential energy is gradually transformed into kinetic energy.
By imitating the analysis of the descending process of the balance wheel, it is concluded that the kinetic energy of the balance wheel is gradually transformed into gravitational potential energy during the ascending process of the balance wheel.
Third, strengthen consolidation.
2. Trampoline analysis: mutual transformation of elastic potential energy and kinetic energy. It is concluded that kinetic energy and elastic potential energy can also be transformed into each other.
There are many examples in nature where kinetic energy and potential energy are transformed into each other. First, analyze the textbook map 15.5? 2. Deepen students' understanding of the transformation of kinetic energy and potential energy, and then ask students to list examples of the transformation of kinetic energy and potential energy in life for teachers and students to analyze together. When going downhill, the bike goes faster and faster, tamping, etc.
Conclusion: Kinetic energy and potential energy can be transformed into each other.
Fourthly, the definition of mechanical energy is introduced: the sum of kinetic energy and potential energy.
Verbs (short for verb) expand knowledge.
1. Do the students work in groups? Thinking about doing it? Ask the students to analyze the causes of this phenomenon and whether there are other energy transformations.
Suppose there is no resistance, what will happen? Deduce the law of conservation of mechanical energy
3. Analyze the change of mechanical energy in table tennis again.
Six, review the old and learn the new
Reading: the scientific world: artificial earth satellites, thinking exercises after class.
Mechanical energy and its transformation teaching design teaching goal
1. Understand the conversion between kinetic energy and potential energy.
2. Understand that mechanical energy is constant.
3. Understand the utilization of hydropower and wind energy.
Emphasis and difficulty in teaching
Understanding the transformation of kinetic energy and potential energy is the key and difficult point in teaching.
teaching process
Study guide 1. Conversion of kinetic energy and potential energy
● Self-preparation:
Read pages 7 1 and 72 of the textbook and complete the following blanks:
1. Gravity potential energy and elastic potential energy are collectively referred to as potential energy, and kinetic energy and potential energy are collectively referred to as mechanical energy.
2. Transformation of kinetic energy and potential energy: kinetic energy and potential energy can be transformed into each other, kinetic energy can be transformed into potential energy, and potential energy can also be transformed into kinetic energy.
3. Hold the chalk head high.
Question:
① Does the lifted chalk tool have no energy? Why?
It has energy because it can do external work.
② What energy is there when the chalk head falls through a certain point?
(At this time, there is both gravitational potential energy and kinetic energy)
③ Analyze and compare the changes of gravitational potential energy and kinetic energy of the chalk head at this position and the initial position.
(Gravitational potential energy decreases and kinetic energy increases)
● Group discussion:
Observe the motion of the rolling pendulum and think about the changes of kinetic energy and potential energy;
Experiment 1: rolling pendulum experiment
① When the balance wheel is released, the balance wheel is stationary at the highest point. At this time, the balance wheel has only gravitational potential energy and no kinetic energy. When the balance wheel descends, its height decreases and its gravitational potential energy decreases. The balance wheel rotates and descends; The faster it rotates, the greater its kinetic energy. When the pendulum turns to the lowest point, it rotates fastest and has the largest kinetic energy; It has the lowest height and the smallest gravitational potential energy. During the descent of the balance wheel, its gravitational potential energy is gradually transformed into kinetic energy.
(2) By analyzing the descending process of the balance wheel, the changes of kinetic energy and potential energy during the ascending process of the balance wheel are obtained.
Experiment 2: simple pendulum experiment
① Hang one end of the pendulum rope on the blackboard, make it swing in front of the blackboard and vibrate in parallel with the blackboard, and record the positions of the left a, right highest point c and lowest point b on the blackboard.
② experimental analysis of simple pendulum:
When the ball swings from point A to point B, the potential energy of gravity is converted into kinetic energy.
During the swing from point B to point C, kinetic energy is converted into gravitational potential energy.
The kinetic energy of the ball is maximum at point B and minimum at point A (or point C).
The gravitational potential energy of the ball is the largest at point A (or point C) and the smallest at point B.
Experiment 3: mutual transformation of elastic potential energy and kinetic energy.
Courseware (or experiment) demonstration: the transformation experiment of kinetic energy and elastic potential energy
● Teacher's guidance:
1. In the process of mutual transformation between kinetic energy and potential energy, there must be their own changes, and they are increasing and decreasing.
2. The increase or decrease of kinetic energy should be judged by the increase or decrease of speed.
3. The increase or decrease of gravitational potential energy should be judged by the increase or decrease of the height of the object from the ground.
4. Judge the increase or decrease of elastic potential energy according to the change of elastic deformation.
● Tracking exercises:
1. Put the wound toy car on a horizontal table, and the toy car will accelerate from a static state. In this process, the energy change of the toy car is (a).
A. elastic potential energy decreases and kinetic energy increases. B. elastic potential energy decreases and kinetic energy decreases.
C. the elastic potential energy increases and the kinetic energy increases. D. elastic potential energy increases and kinetic energy decreases.
2. In the following phenomena, it is (c) that converts kinetic energy into gravitational potential energy.
3. As shown in the picture, a small ball slides freely on a stationary smooth surface. If its gravitational potential energy at the top is 65J, the kinetic energy of sliding to the bottom is (D).
A.35J B.50J C.55J D.65J
Study guide II. Conservation of mechanical energy
● Self-preparation:
Look at the textbook 7 1, 72, 73, Science World? Mechanical energy conversion of artificial earth satellite? Fill in the blanks after the content:
The satellite orbits the earth in an elliptical orbit. The closest point to the earth is called perigee, and the farthest point is called apogee. The kinetic energy of a satellite is the largest at perigee and the gravitational potential energy is the smallest, while the kinetic energy of a satellite at apogee is the smallest and the gravitational potential energy is the largest. In the process of satellite moving from perigee to apogee, the satellite speed slows down, the kinetic energy decreases and the gravitational potential energy increases. In the process of moving from apogee to perigee, the speed of the satellite increases, the kinetic energy increases and the gravitational potential energy decreases.
● Group discussion:
Experiment: Hang an iron lock with a rope. Hold the iron lock near your nose, let go when it is stable, and don't move your head. The iron lock swings back and forth. Will it touch your nose when it swings back? If there is only the conversion between kinetic energy and potential energy, why didn't you touch your nose? How has the total amount of mechanical energy changed?
The movement of the iron lock should overcome the air resistance, consume a part of mechanical energy and reduce the total amount of mechanical energy. The iron lock will not return to its original height, so it will not touch the nose.
● Teacher's guidance:
Law of conservation of mechanical energy: if only kinetic energy and potential energy are transformed into each other, the sum of mechanical energy remains unchanged (conservation).
● Tracking exercises:
1. This artificial satellite orbits the earth in an elliptical orbit. When it moves from perigee to apogee, the kinetic energy of the satellite decreases (optional? Increase? 、? Reduce? 、? The same? ), the satellite potential energy increases (optional? Increase? 、? Reduce? 、? The same? )
2. play? Roller coaster? This is a very exciting entertainment. As shown in the figure, the roller coaster sometimes rises from the lowest point D to the highest point A, and sometimes flies down from the highest point A. During the roller coaster movement, if energy loss is not counted, only kinetic energy and potential energy are transformed into each other. The following statement is true (b)
The mechanical energy of point A is less than that of point B, the kinetic energy of point B.D is the largest, and the potential energy of point A is the largest.
The kinetic energy at point C.D is the largest, and the mechanical energy at point A is the largest. The potential energy and mechanical energy of point D.A are the largest.
Study guide 3. Utilization of hydropower and wind energy
● Self-preparation:
Read pages 72 and 73 of the textbook and complete the following blanks:
(1) Running water and wind in nature are natural resources with a lot of mechanical energy;
(2) let the water flow impact the water wheel to rotate to pump water, grind and generate electricity;
The wind of the ship swelled the sails to push it forward.
(4) Blower and windmill can drive generators to generate electricity.
● Group discussion:
1. Why do people build dams to raise the upstream water level for hydropower generation?
2. In the utilization of wind energy, what other forms of energy can wind energy be converted into?
● Teacher's guidance:
The barrage raises the upstream water level, which increases the gravitational potential energy of water, which can be converted into kinetic energy of water to drive the turbine to rotate, and then drive the generator to generate electricity.
● Tracking exercises:
1. About the utilization of water energy, the following statement is wrong (D).
A. the kinetic energy of water flow drives the turbine to rotate.
B. The more kinetic energy of water, the more work the turbine can do.
The higher the water level in the upper reaches of the river, the greater the potential energy of water, and the greater the kinetic energy converted from potential energy.
The turbine should be installed upstream before the dam.
2. The following statement about wind energy is incorrect (c).
A. wind energy will not pollute the environment. B. wind energy is not easy to store.
C. wind energy is stable. Wind energy is easy to use.
3. Does Dezhou Development Zone use maps? The scenery complements each other? Landscape lighting. It? Expenses? Small fan? Shoulder? Photovoltaic panels? Waist? Lighting? Pedal? Batteries. The following explanation is reasonable (c)
A. photovoltaic panels convert electric energy into light energy.
B. Lighting is to convert internal energy into electric energy.
C. Small fans use wind power to generate electricity and convert mechanical energy into electrical energy.
D, the battery discharges at night, converting electric energy into chemical energy.