"Experiment: Verification of the Law of Conservation of Mechanical Energy" Excellent Courseware on the Law of Conservation of Mechanical Energy PPT

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"Experiment: Verification of the Law of Conservation of Mechanical Energy" Excellent Courseware on the Law of Conservation of Mechanical Energy PPT

Part One: Learning Objectives

1. Clearly verify the basic idea of ​​the law of conservation of mechanical energy and be able to measure related quantities.

2. Be able to perform experimental operations correctly, analyze experimental data to draw conclusions, and qualitatively analyze the causes of errors.

Verification of the law of conservation of mechanical energy PPT, part 2: 01 Clarify the principle and refine the method

1. Experimental ideas

The premise of conservation of mechanical energy is that "only ___________ does work", so the research process must meet this condition. In this experiment, we will study the process in which only gravity does work.

2. Measurement and data analysis of physical quantities

When only gravity does work, only the conversion of gravitational potential energy and kinetic energy occurs.

(1) The expression to be verified: 12mv22+mgh2=__________ or: 12mv22-12mv12=__________.

(2) Physical quantities to be measured: ________ between the two positions of the object, and ________ of the object.

3. Reference cases

Case 1: Studying the mechanical energy of freely falling objects

1. Experimental equipment

Iron stand (with iron clamp), ______________, weight (with clamp), ________, carbon paper (or toner disk), wires, millimeter scale, AC power supply.

2. Experimental steps

(1) Installation device: Install the dotting timer on the iron stand as shown in Figure 1A, and connect the dotting timer and the power supply with wires.

(2) Paper tape: Fix the heavy object with a clip on one end of the paper tape, and pass the other end through the limit hole of the dot timer. Lift the paper tape vertically with your hands to make the heavy object stop near the dot timer. First After turning on the power, release the paper tape and let the heavy object pull the paper tape to fall freely. Repeat several times to get 3 to 5 dotted paper tapes.

(3) Select a paper tape and measure: Select a paper tape with clear dots, determine the start and end positions to be studied, measure the distance Δh between the two positions and the speed at the two positions, and substitute it into the expression for verification.

3.Data processing

(1) Calculate the instantaneous velocity corresponding to each point: As shown in Figure B, according to the formula vn=hn+1-hn-12T, calculate the instantaneous velocity vn of a certain point.

(2) Verification of the law of conservation of mechanical energy

Method 1: Use the starting point and the nth point.

Select a paper strip with a distance between the first two points close to 2 mm, and the first point is the starting point. If mghn=12mvn2 is within the allowable range of the experimental error, the law of conservation of mechanical energy has been verified.

Method 2: Pick any two points A and B.

If mghAB=12mvB2-12mvA2 is within the allowable range of experimental error, the mechanical conservation law is verified.

Method 3: Image method (as shown in Figure 2).

If the graph is a straight line passing through the origin and with a slope of g within the allowable range of experimental errors, the law of conservation of mechanical energy is verified.

4.Error analysis

The error in this experiment is mainly caused by the accidental error caused by the measurement of the paper tape, the air resistance in the movement of the weight and paper tape, and the systematic error caused by the ____________ of the dotting timer.

5. Experimental precautions

(1) When installing the dot timer, make sure that the center lines of the two limit holes are on the same ______ line to reduce frictional resistance.

(2) Heavy objects with higher mass and density should be selected. ______ density can reduce the volume and relatively reduce the impact of air resistance.

(3) During the experiment, the power should be turned on first, let the dotting timer work normally, and then the paper tape should be released to let the heavy object fall.

(4) Several verification methods in this experiment all ______ (fill in “required” or “unnecessary”) to measure the mass m of the weight.

Verification of the Law of Conservation of Mechanical Energy PPT, the third part of the content: 02 refined analysis of classic questions to improve capabilities

1. Study the mechanical energy of freely falling objects

Example 1 (End of the first semester of 2018·Shuangfeng No. 1 Middle School) When a student used the device shown in Figure 4A to "verify the law of conservation of mechanical energy", the frequency of the AC power supply used was 50 Hz, and the paper tape shown in Figure B was obtained. Select five consecutive points A, B, C, D, and E printed on the paper tape, and measure the distance between point A and the starting point O to be s0 = 19.00 cm, the distance between points A and C to be s1 = 8.36 cm, and the distance between point C to The distance between , E is s2=9.88 cm, g is 9.8 m/s2, and the measured mass of the heavy object is m=1 kg.

(1) Which of the following practices is correct _________.

A. The mass of the weight and the clamp must be weighed

B. The two limit holes in the picture must be on the same vertical line

C. Pass the paper tape with the heavy object through the limit hole, hold it with your hand, and keep your hand as close to the dotting timer as possible

D. During the experiment, first release the paper tape, and then turn on the power of the dotting timer.

E. When processing data, two points that are closer to each other on the paper should be selected as the initial and final positions.

(2) Select points O and C as the initial and final positions to verify the law of conservation of mechanical energy. The gravitational potential energy reduced by the weight is _____J, and the speed of the weight when hitting point C is _____ m/s. (Retain all three results. (significant digits)

(3) Calculate the speed v of the weight when dropping each point based on the paper tape, and measure the falling distance s. Then the image drawn with as the ordinate and s as the abscissa should be ________ among the following options.

2. Study the mechanical energy of an object sliding along an inclined plane

Example 2: Now use the device shown in Figure 5 to "verify the law of conservation of mechanical energy". In the figure, AB is a fixed smooth inclined plane, the inclination angle of the inclined plane is 30°, 1 and 2 are two photoelectric gates fixed at appropriate positions on the inclined plane, and The photoelectric timers they are connected to are not shown. Let the slider slide down from the top of the slope. The photoelectric timers connected to photoelectric gates 1 and 2 display the light blocking time of 5.00×10-2 s and 2.00×10- respectively. 2 s. It is known that the mass of the slider is 2.00 kg, the length of the slider along the inclined plane is 5.00 cm, the distance between photogate 1 and 2 is 0.54 m, g is 9.80 m/s2, and when the slider passes the photogate The speed of is its average speed. (Results retain three significant figures)

(1) The speed v1 when the slider passes through photoelectric gate 1 =________ m/s, and the speed v2 when it passes through photoelectric gate 2 = ______ m/s.

(2) The increase in kinetic energy of the slider when it passes between photogates 1 and 2 is ______ J, and the decrease in gravitational potential energy is _________ J.

Verification of the law of conservation of mechanical energy PPT, part 4: 03 in-class drills, point-by-point implementation

1. Figure 8 is a schematic diagram of the experimental device for "verifying the law of conservation of mechanical energy". The existing equipment is: an iron stand with a clamp, an electromagnetic dotting timer, paper tape, and a weight with a clamp. Answer the following questions:

(1) In order to complete this experiment, in addition to the equipment provided, the equipment also needed is _____.

(Insert the letter before the correct option)

A.Meter stick

B. Stopwatch

C. Low voltage DC power supply

D. Low voltage AC power supply

(2) The reasons for the errors in the experiment are: ① There is friction between the paper tape and the dotting timer. ② There is an error in the reading when measuring the position of the point on the paper tape with a meter ruler. ③ When calculating the change of potential energy, the beginning and end of the selected The position is too close. ④ There is air resistance (choose any two)

(Just write down two reasons).

(3) In the experiment, because the two limit holes of the dotting timer are not on the same vertical line, the paper tape will encounter greater resistance when passing through, which will cause ________.

2. (At the end of the first semester of high school in Guiyang City, 2018) A student used the experimental device shown in Figure 9(a) to "verify the law of conservation of mechanical energy". Figure (b) is a line recorded with a 6 V, 50 Hz dot timer. Paper tape, point O is the starting point of the weight's fall. The distances from the selected counting points A, B, C, D to point O are marked in the figure. The acceleration of gravity g is 9.8 m/s2, and the mass of the weight is 1 kg. (Calculation results retain two significant figures)

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Update Time: 2024-11-22

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