Device for verifying centripetal force expression in motion of conical pendulum by adopting electric spark timer

Abstract

The utility model discloses a device for verifying a centripetal force expression in motion of a conical pendulum by adopting an electric spark timer, a hand-cranking lifting device is placed at the lower center position of a support, a long-shaft low-speed motor is fixed in the middle of the support, and the electric spark timer and a motor power supply box are respectively fixed on the left side and the right side of the support; an optical disc is fixed on a rotating shaft of the long-shaft low-speed motor, a layer of tin foil paper is adhered on the optical disc, and two graphite lines are suspended at two centrosymmetric positions of the optical disc; two small insulating balls are hung at the lowest ends of the two graphite wires; the electric brush is fixed on the inner side of the support right above the optical disc, the upper end of the electric brush is a metal spring end, the lower end of the electric brush is a graphite end, and the graphite end is conductive with tin foil paper on the rotating optical disc in the continuous contact friction process. The device can accurately and quantitatively verify the centripetal force expression, makes up the gap that the centripetal force expression cannot be quantitatively obtained through student experiment exploration in high school physics teaching, and has a stronger enlightenment effect on innovative thinking of students.

Description

Technical Field

[0001] The utility model belongs to teaching demonstration instruments. Background Art

[0002] The qualitative experiment of the centripetal force expression is used to explore which physical quantities are related to the centripetal force. The semi - quantitative experiment, that is, the centripetal force demonstrator experiment, is used to explore the ratio relationship between the centripetal force magnitude and several physical quantities. During the learning process, students cannot directly prove through quantitative experiments that the centripetal force magnitude is indeed as described in the textbook expression. Moreover, the error of students controlling the conical pendulum movement by hand is very large, and the experimental results cannot well verify the correctness of the centripetal force formula, reducing the value and significance of this experiment. Summary of the Invention

[0003] The purpose of the utility model is to provide a device that uses an electric spark timer to verify the centripetal force expression in the conical pendulum movement, verifies the centripetal force expression in the conical pendulum movement in high school physics textbooks, has small errors, and fills the gap in the quantitative verification experiment of centripetal force in high school physics.

[0004] The technical solution of the utility model is a device that uses an electric spark timer to verify the centripetal force expression in the conical pendulum movement, which is characterized in that: the hand - cranked lifting device is placed at the central position under the bracket. A long - shaft low - speed motor is fixed in the middle of the bracket. An electric spark timer and a motor power supply box are respectively fixed on the left and right sides of the bracket. A metal plate is fixed on the hand - cranked lifting device, and a layer of carbon powder paper is laid on the metal plate, and a layer of white paper is laid on the carbon powder paper. A disc is fixed on the rotating shaft of the long - shaft low - speed motor, and a layer of tin foil paper is stuck on the disc, and two graphite wires are suspended at two symmetric positions in the center of the disc. Two insulating small balls are suspended at the lowest ends of the two graphite wires. A plumb line is fixed at the lower end of the rotating shaft of the long - shaft low - speed motor, located at the center of the connection line of the two insulating small balls. The carbon brush is fixed on the inner side of the bracket directly above the disc through hot melt adhesive and transparent tape. The upper end of the carbon brush is a metal spring end, and the lower end is a graphite end. The graphite end conducts electricity during the continuous contact and friction with the tin foil paper on the rotating disc. Two double - headed alligator clip high - voltage pulse output wires, one wire is clamped to the edge of the metal plate at one end and to the positive pole of the electric spark timer at the other end, and the other wire is clamped to the metal spring end of the carbon brush at one end and to the negative pole of the electric spark timer at the other end.

[0005] Further, a discharge needle is placed inside one of the insulating small balls in the direction of the graphite wire, and the discharge needle extends 2 millimeters out of the small hole at the lower end of the ball.

[0006] The utility model has the following beneficial effects:

[0007] The device of the utility model uses an electric spark timer to verify the expression of centripetal force in the conical pendulum movement, providing a new teaching demonstration instrument. By using the electrostatic adsorption and powder grinding function and the timing function of the electric spark timer, the centripetal force formula in the conical pendulum movement in the textbook is verified, which is intuitive and scientific. On the one hand, it reduces the experimental error and improves the accuracy to 99%; on the other hand, through the dotting and timing function of the electric spark timer, the position information and time information of the conical pendulum movement are left and visualized, expanding and diverging the physical thinking of students, and inspiring and cultivating the innovative awareness of students. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic structural diagram of the utility model;

[0009] Figure 2 is a schematic structural diagram of an insulating small ball with a discharge needle inside;

[0010] Figure 3 is a schematic diagram of the expected principle of the test result;

[0011] Figure 4 is a graph of the actual data of the test result;

[0012] Figure 5 is a graph of the geometric data relationship of the conical pendulum movement;

[0013] Figure 6 is a force analysis diagram of the small ball;

[0014] Explanation of the reference numerals in the drawings: Hand-cranked lifting device 1, metal plate 2, bracket 3, motor power supply box 4, motor knob 5, long-shaft low-speed motor 6, electric spark timer 7, double-headed alligator clip high-voltage pulse output wire 8, brush 9, optical disc 10, graphite wire 11, plumb line 12, two insulating small balls 13, discharge needle 14. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] As Figure 1As shown in the figure, a device for verifying the centripetal force expression in the conical pendulum motion using an electric spark timer. The hand-cranked lifting device 1 is placed at the central position under the bracket. A long-axis low-speed motor 6 is fixed in the middle of the bracket. An electric spark timer 7 and a motor power supply box 4 are respectively fixed on the left and right sides of the bracket. A metal plate 2 is fixed on the hand-cranked lifting device 1. A layer of carbon paper is laid on the metal plate 2, and a layer of white paper is laid on the carbon paper. A CD 10 is fixed on the rotating shaft of the long-axis low-speed motor 6. A layer of tin foil paper is adhered to the CD 10, and two graphite wires 11 are suspended at two symmetric positions at the center of the CD 10. Two insulating small balls 13 are suspended at the lower ends of the two graphite wires 11. A plumb line 12 is fixed at the lower end of the rotating shaft of the long-axis low-speed motor 6, located at the center of the connection line of the two insulating small balls 13. The brush 9 is fixed on the inner side of the bracket directly above the CD through hot melt adhesive and transparent tape. The upper end of the brush is a metal spring end, and the lower end is a graphite end. The graphite end conducts electricity during the continuous contact and friction with the tin foil paper on the rotating CD. Two double-headed alligator clip high-voltage pulse output wires 8. One end of one wire is clipped to the edge of the metal plate, and the other end is clipped to the positive electrode of the electric spark timer. One end of the other wire is clipped to the metal spring end of the brush, and the other end is clipped to the negative electrode of the electric spark timer.

[0016] There are two motor knobs 5, one for speed adjustment and the other for adjusting the rotation direction.

[0017] As Figure 2 shown, a discharge needle 14 is placed inside one of the insulating small balls 13 in the direction of the graphite wire. The discharge needle 14 extends about 2 mm out of the small hole at the lower end of the ball.

[0018] (I) Device Usage Instructions

[0019] 1. Determine the center of the circle through the plumb line 12. Connect the power supply of the long-axis low-speed motor 6, and use the motor knob 5 to adjust the speed so that the two insulating small balls 13 perform a suitable and stable conical pendulum motion.

[0020] 2. Rotate the hand-cranked lifting device 1 to raise the metal plate 2 to a position very close to the motion plane of the two insulating small balls 13 (Note: Generally, control the distance within 8 mm).

[0021] 3. Connect the power supply of the electric spark timer 7, so that the metal plate 2 is positively charged by the electric spark timer 7 through the high-voltage pulse output wire 8. At the same time, the brush 9 is negatively charged by the electric spark timer 7. The brush 9 contacts the tin foil paper on the CD 10, the tin foil paper then contacts the graphite wire 11, and the graphite wire 11 contacts the discharge needle 14 inside the ball, finally making the discharge needle 14 inside the ball negatively charged.

[0022] 4. Since the discharge needle 14 is negatively charged and the metal plate 2 is positively charged, a continuous discharge phenomenon will occur between the tip of the discharge needle and the metal plate 2, with a frequency of 50 Hz, that is, a discharge occurs every 0.02 seconds, and a toner powder dot is formed every 0.02 seconds.

[0023] 5. Since there is a large amount of toner powder on the metal plate 2, the toner powder will be attracted upward by the tip electric spark during discharge, and thus a graphite dot trace will fall on the white paper above it. When observing that the discharge is approaching a full circle, turn off the electric spark timer 7 and turn off the long-axis low-speed motor 6.

[0024] (2) Explanation of the method for obtaining experimental data

[0025] 1. Use a millimeter scale to measure the height h of the metal plate 2 from the optical disc 10 at this time, as Figure 5 ;

[0026] 2. Use a compass to draw a circle with a suitable radius so that as many ground powder dots as possible fall on the circle. Select several toner powder dots with equal consecutive radii and measure the dotting radius r 1 and r 2 , as Figure 4 ;

[0027] 3. Connect the center O and the left and right endpoints A and B of the four selected ground powder dots, and use a protractor to measure the rotated angle α, as Figure 4 ; Convert α into radian system according to the angle-radian conversion relationship.

[0028] (3) Explanation of the method and principle for verifying the centripetal force formula

[0029] Since the small ball is doing uniform circular motion with a stable rotational speed, the partial circle formed by the graphite powder trace on the white paper can record the corresponding positions of the small ball at each moment when it is doing conical pendulum motion. Note: Since the timing of turning off the electric spark timer needs to be judged by the students themselves, if the discharge exceeds one circle, there will be overlapping dot traces of two circles at some arc positions, and the students cannot accurately distinguish which toner powder dot is from the first circle and which is from the second circle. Therefore, in order to make the dot traces accurate, clear and easy to distinguish, usually turn off the electric spark timer when observing that the discharge exceeds half a circle and is almost one circle, so as to ensure that each toner powder dot is from the same circle of conical pendulum motion.

[0030] From the geometric relationship diagram ( Figure 5 ) and the force analysis diagram ( Figure 6 ), it can be known that the angle between the rope and the horizontal direction, the angle between the rope tension (along the direction of rope contraction) and the centripetal force (horizontal direction) are exactly the same, and are represented by the letter θ.

[0031] Figure 5 、 Figure 6The angles θ of the two figures are the same, and the tangents of this angle θ should also be the same. Therefore, verifying that the tangents of the same angle θ in the geometric figure and the force diagram are the same can prove that the formula is correct, that is, the results of Formula 1 and Formula 2 should be the same, where Formula 2 gives the centripetal force expression F in the textbook 向 = mω 2 r.

[0032]

[0033] Then the relational expression to be verified in the experiment is as follows: where d is the distance between the suspension points of the two small balls, and r is the average value of r 1 and r 2 , and g is taken as 9.8 m / s 2 .

[0034] (IV) Processing of Experimental Real Data and Results

[0035] Figure 4 This is the toner dot pattern obtained during a student experiment with this experimental device. Through measurement, the data obtained are: h = 28.00 cm, r 1 = 12.60 cm, r 2 = 12.60 cm, α = 17.5°. It is also known that d = 6.40 cm, which was measured during the fabrication of the experimental device.

[0036] From the measured data of the radius, it can be seen that the distances from the 4 toner dots we selected to the center of the circle are the same. During this period, the small ball makes a stable conical pendulum motion, and the arc formed by these four toner dots punched by the discharge needle is part of a standard uniform circular motion. The experimental data are very ideal.

[0037] The radian through which this small arc turns can be determined by the measured data of the angles turned by the four toner dots During this process, the angular velocity of the uniform circular motion of the small ball can be determined as

[0038] In the geometric relation diagram, there should be a relational expression In the force diagram, there should be a relational expression where r should be the average value of r 1 and r 2

[0039] Substitute the measured data and the determined data into the two formulas (1) and (2), we get:

[0040]

[0041] (V) Error Analysis

[0042] ​The absolute error E = 3.0044 - 2.9787 = 0.0257;

[0043] Relative error

[0044] Note: The final relative error of this experiment is only 0.86%, indicating that this device can accurately quantitatively verify the accuracy of the centripetal force expression, filling the gap in high school physics teaching that the centripetal force expression cannot be quantitatively obtained through student experiments. Moreover, there are many one-shot videos of the experimental operation process and data acquisition process, which are highly authentic, including Figure 4 This experiment with extremely small errors shown. During the video shooting process, the data measurement process is also clearly and continuously presented.

[0045] (VI) Experimental value

[0046] With the popularization of digital and information education technologies, more and more digital experiments are now applied to teaching, such as many experiments related to sensors. However, since sensor experimental equipment is not popularized in all regions, for example, the school where the author is located has not used sensor experimental equipment for student experiments. Therefore, using the first experimental instrument learned by students in high school, the spark timer, for experiments can be popularized and applied in all regions of the country.

[0047] In addition, although it is very intuitive and convenient to obtain data through a computer with sensors, it also leaves little room for students to think. This experiment has a stronger inspiration for students' innovative thinking, meets the requirements of the current core literacy of the physics discipline, and helps to cultivate innovative talents.

Claims

1. A device for verifying the centripetal force expression in the motion of a conical pendulum using an electric spark timer, characterized in that: The hand-cranked lifting device (1) is placed at the center of the bracket, a long-axis low-speed motor (6) is fixed in the middle of the bracket, and a spark timer (7) and a motor power box (4) are respectively fixed on the left and right sides of the bracket; a metal plate (2) is fixed on the hand-cranked lifting device (1), a layer of toner paper is laid on the metal plate (2), and a layer of white paper is laid on the toner paper; an optical disc (10) is fixed on the rotating shaft of the long-axis low-speed motor (6), a layer of tin foil is adhered on the optical disc (10), and two graphite wires (11) are hung at two symmetrical positions at the center of the optical disc (10); two insulating wires (11) are hung at the bottom ends of the two graphite wires (11). The invention relates to a small ball (13); a weight wire (12) fixed at the lower end of the rotating shaft of the long-axis low-speed motor (6), located at the center of the line connecting the two insulating small balls (13); a brush (9) fixed to the inner side of the bracket just above the optical disc by hot-melt adhesive and transparent tape, the upper end of the brush is a metal spring end, and the lower end is a graphite end, and the graphite end and the tin foil on the rotating optical disc are constantly in contact and friction to conduct electricity; two double-ended alligator clip high-voltage pulse output wires (8), one end of one of the wires is clamped to the edge of the metal plate, and the other end is clamped to the positive electrode of the electric spark timer, and one end of the other wire is clamped to the metal spring end of the brush, and the other end is clamped to the negative electrode of the electric spark timer.

2. The device for verifying the centripetal force expression in the conical pendulum motion using an electric spark timer as claimed in claim 1, characterized in that one A discharge needle (14) is placed inside the insulating ball (13) in the direction of the graphite line, and the discharge needle extends 2 mm from the small hole at the lower end of the ball.

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