"Experiment: Verify the Law of Conservation of Mechanical Energy" Law of Conservation of Mechanical Energy PPT

Description

"Experiment: Verify the Law of Conservation of Mechanical Energy" Law of Conservation of Mechanical Energy PPT

Part 1: Essential knowledge and foundation of literacy

【Purpose】

Learn the experimental methods and skills of using a dot timer to verify the law of conservation of mechanical energy.

【experiment equipment】

Iron stand (including iron clamps), dotting timer, student power supply, paper tape, carbon paper, wires, millimeter scale, weights (paper tape clip).

[Experimental Principle and Design]

1. The basic idea of ​​the experiment - confirmatory experiment:

Verify that in free fall, the reduced gravitational potential energy and increased kinetic energy of an object during the falling process are equal. Experimental principle:

(1) In the free fall motion where only gravity does work, the gravitational potential energy and kinetic energy of the object are converted into each other, but the total mechanical energy remains unchanged. If the instantaneous speed of the object at a certain moment is v and the falling height is h, then the decrease in gravitational potential energy is mgh and the increase in kinetic energy is mv2. See whether they are equal within the allowable range of experimental error. If they are equal, the law of conservation of mechanical energy is verified. .

(2) Method to calculate the speed of hitting the nth point: measure the distance xn and xn+1 between the nth point and the adjacent points before and after, and calculate it by the formula vn=_____ or vn=_____, as shown in the figure :

2. Experimental design - measurement methods of two physical quantities:

(1) Measurement of height h

Use a scale to measure the height h of the falling object.

(2) Measurement of speed v

The instantaneous speed of a certain point is calculated by using the average speed of a certain period of time in uniform linear motion to be equal to the instantaneous speed of the middle moment of this period of time.

Experimental verification of the law of conservation of mechanical energy PPT, the second part of the content: key capabilities and literacy formation

【experiment procedure】

1. Experimental steps

1. Installation: Fix the checked and adjusted dotting timer vertically on the iron stand as shown in the figure, and connect the circuit.

2. Paper tape: Fix one end of the paper tape on the heavy object with a clip, and pass the other end through the limit hole of the dot timer. Hold the paper tape with your hand to keep the weight stationary close to the dot timer. Turn on the power first, then loosen the paper tape, and let the heavy object fall freely with the paper tape. Repeat the experiment 3 to 5 times by replacing the paper tape.

3. Select paper tape:

(1) When verifying with _____=mghn, a paper tape with clear dots and a distance between points 1 and 2 less than or close to 2 mm should be selected. If the distance between points 1 and 2 is greater than 2 mm, this is caused by releasing the paper tape first and then turning on the power. In this way, the first point on the paper tape is not the starting point of the movement, and such paper tape cannot be selected.

(2) When verifying with _____=mgΔh, due to the relativity of gravitational potential energy, when processing the paper tape, select an appropriate point as the reference point, so that the distance between the 1st and 2nd points printed on the paper tape is 2 mm It doesn't matter, so it can be used as long as the subsequent dots are clear.

【Think·Discussion】

(1) What aspects of operational safety should be paid attention to during the experiment? (Scientific attitude and responsibility)

Tip: When installing the dotting timer, it must be mounted vertically and steadily so that the two limit holes are on the same vertical line to reduce frictional resistance.

(2) What should you pay attention to when using the dot timer?

Tips: Turn on the power first and let the dotting timer work normally, then loosen the paper tape and let the heavy object fall.

Experimental verification of the law of conservation of mechanical energy PPT, the third part of the content: Experimental analysis·Literacy transfer

Type 1 Experimental Operation

[Typical Example 1] A student used the experimental device shown in Figure A to verify the law of conservation of mechanical energy. The power supply used in the experiment is a student power supply, which can provide AC and DC power with an output voltage of 6 V, and the frequency of AC power is 50 Hz. The heavy hammer starts falling from a high place and starts falling from a standstill. The paper tape dragged by the weight hammer makes a series of points. By measuring and analyzing the points on the paper tape, the law of conservation of mechanical energy can be verified.

(1) He performed the following steps:

A. Install the device according to the device shown in the diagram;

B. Connect the dotting timer to the "DC output" of the power supply;

C. Use a balance to measure the mass of the weight;

D. Turn on the power first, then release the paper tape and print out a paper tape;

E. Measure the distance between certain points on the paper tape;

F. Based on the measurement results, calculate whether the reduced gravitational potential energy during the falling process of the weight is equal to the increased kinetic energy.

The unnecessary steps are _______________, and the improper steps are _______________.

(2) After correct operation, this student selected a piece of paper tape with clear dots for measurement and analysis, as shown in Figure B. Among them, point O is the starting point, and A, B, C, D, E, and F are the six counting points. According to the measurement data on the paper tape, the speed of the weight when hitting point B is ____________m/s. (Keep 3 significant figures)

(3) He continued to calculate the speed v of each point based on the paper tape, measured the falling distance h, and drew an image with h as the vertical axis and h as the horizontal axis, which should be ____________ in Figure C.

Type 2 Data processing

[Typical Example 2] Use the experimental device in Figure 1 to verify the conservation of mechanical energy in the system composed of m1 and m2. M2 starts to fall from a high place from rest. The paper tape dragged on M1 makes a series of points through a dotting timer. By measuring the points on the paper tape, the law of conservation of mechanical energy can be verified. Figure 2 shows a paper tape obtained in the experiment: 0 is the first point laid down, and there are 4 points (not marked in the picture) between every two adjacent counting points. The distance between the counting points is as shown in the figure 2 shown. It is known that m1=50 g, m2=150 g, and the falling distance of m2 is h, then (the result retains two significant figures):

(1) The speed v=______m/s when the counting point 5 is marked on the paper tape.

(2) In the process from 0 to 5, the increase in kinetic energy of the system ΔEk=________J, and the decrease in potential energy of the system ΔEp=_______J (g is taken to be 10 m/s2 during calculation). The conclusion drawn from this is:_____________.

(3) If a student makes a -h image as shown in Figure 3, then the local gravity acceleration g=____________m/s2.

【Problem Solving Exploration】

(1) How to find the instantaneous speed of counting point 5?

Tip: According to the fact that the instantaneous speed at the midpoint of time in a linear motion with constant speed is equal to the average speed in the process, the speed when counting point 5 is hit can be calculated.

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Update Time: 2024-07-28

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