Hu Yide, No. 1 Middle School, Yunxi District, Yueyang City, Hunan Province
1. The position and role of the experiment in the textbook
"Flat throwing motion" is the content of Chapter 5 of the compulsory high school physics 2. The content of the course standard is: the projectile motion will be analyzed by the method of motion synthesis and decomposition. The method of motion synthesis and decomposition is an important physical method, which is the focus of this chapter. Flat throw motion is an example application of this method, which is a turning point for students to learn motion from straight line to curve. In this lesson, students are allowed to truly understand the horizontal throwing movement through experiments.
2. Experimental prototypes and deficiencies
1. Experimental prototype
In the new textbook, the horizontal throwing motion experiment provides three cases as shown in Figure 1: sloped small groove with vertical white paper method, water column method, and digital camera method.
Figure 1 Reference case
2. The shortcomings of the original experiment
(1) It is not easy to determine the position of the flat ball throwing motion with the small inclined groove and the vertical white paper method. The experimental error is very large and the time is very long.
(2) The trajectory of the water column method is greatly affected by air resistance and is unstable.
(3) Neither method explores the nature of the dichotomy.
(4) The cost of the digital camera method is too high to promote.
In short, none of the three methods can quickly and accurately record the position of the ball's flat toss movement and trace the trajectory of the flat toss movement.
3. Experimental innovation and improvement
The author has made innovations and improvements on the sloped small groove and vertical white paper method.
One of the innovations: the nature of the two-part movement of the horizontal and vertical movements of the horizontal throwing movement can be explored.
The second innovation: when exploring the trajectory experiment of the flat toss movement, the horizontally and vertically placed tracing board was changed to a vertically movable board facing the chute.
The third innovation: change the position of "finding" the ball toss movement to the position where the ball "plays" the toss movement.
In short, experiments with innovative experimental devices can more accurately describe the trajectory, and can deeply study the law of horizontal throwing motion.
4. Experimental equipment
Self-made flat toss motion detector, student power supply, scale, white paper, carbon paper, small steel ball, etc. (as shown in Figure 2).
Figure 2 Experimental equipment
5. Experimental principle and device description (including experimental device plan)
1. Experimental principle
The horizontal throwing motion can be decomposed into free-fall motion in the vertical direction and uniform linear motion in the horizontal direction.
Vertical application: Horizontal application:
2. Device description
Inclined groove, horizontal groove, heavy vertical line, electromagnet, switch, projection line of the centerline of the inclined groove on the base plate, parallel slot in vertical and horizontal direction Radius), slot spacing 5cm (different track board size different spacing, so that the ball movement track from the upper left corner to the lower right corner).
3. Plan view of experimental device (as shown in Figure 3)
Figure 3 Plan view of the experimental device
6. Experimental process
1. Explore the nature of the two-point movement of the flat throw
(1) Explore the experiment that the horizontal direction of the horizontal throwing motion is a uniform linear motion: take two identical balls (A, C), one placed in the upper left corner of the device at a certain height away from the horizontal end with an electromagnet, and the other One is placed in the lower left corner of the device at the same height as the horizontal end of the chute, and is attracted by the electromagnet. Use a switch to control two small balls to move at the same time, one to perform a flat toss motion, and one to perform an approximately uniform linear motion. It can be seen that they are almost on the same vertical line during the entire process of movement, and finally collide. Inspire students to analyze and let them conclude that the horizontal throw motion is a uniform linear motion in the horizontal direction.
(2) Explore the experiment that the vertical throwing motion is free-falling in the vertical direction: take two identical balls (A, B), one is placed at a certain height in the upper left corner of the device (smooth) and sucked with an electromagnet Hold, the other is placed at the same height in the right corner of the device and sucked by the electromagnet. Automatic control by switch: A ball moves horizontally at the moment of leaving the end of the chute, and B ball falls simultaneously for free-fall movement. It can be seen that they fall to the ground almost simultaneously during the whole process of falling. Inspire students to analyze and let students conclude that the horizontal throw motion is a free fall motion in the vertical direction.
2. Explore the trajectory of flat throw
(1) Take out the trace board and paste white paper and carbon paper on it.
(2) Insert the trace board into the first slot and align the first vertical line with the center line of the chute.
(3) Let the ball roll freely from a certain height of the chute, collide with the trace board, and write down the initial position 1 of the flat throw of the ball (ie, the origin of coordinates) on the white paper of the trace board.
(4) Then insert the tracing board horizontally into the latter slot and at the same time move the tracing board longitudinally inward by a slot distance (to ensure that the horizontal displacement of the ball is unchanged) so that the second bar on the tracing board is vertical Align the line with the centerline of the chute, let the ball roll freely from the same height of the chute, collide with the tracer board, and record the position of the flat throw of the ball 2 on the white paper of the tracer board.
(5) According to the same method, record the ball throwing positions 3, 4, 5, 6.
(6) Open the carbon paper, and connect the points with a smooth curve according to the trace points on the white paper of the trace board, which is the track of the flat throw motion.
(7) Contrast experiment: let the ball roll freely from the same height of the chute, and observe whether the trajectory of the ball's flat throw coincides with the traced trajectory.
7. Experimental effect
The improved experimental device improves the accuracy of the experiment and shortens the experiment time. The experimental operation is simple and the physical thought is outstanding. Using this instrument, you can quickly and accurately record the position of the ball's horizontal throw motion and trace the trajectory of the horizontal throw motion. Use the obtained traces to further study the law of horizontal throw motion.
8. Self-evaluation
This experimental device is mainly improved in the way of "recording the ball position". Transform the trajectory of simply observing the flat toss movement into an intuitive and scientific depiction of the trajectory of the toss movement, and analyze the laws of motion according to the points on the trajectory. In teaching, it can be designed as a demonstration experiment, and can also be designed as a group experiment for students, allowing students to do it by themselves. In the process of the experiment, students' knowledge transfer ability and innovative thinking ability are cultivated.
Such instruments may create process errors and operational errors. Because it can make up for some shortcomings in the experimental teaching of horizontal throwing, it has certain practical value.
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