Sections: Physics
Educational: learn how to measure the potential energy of a body raised above the ground and a deformed spring, compare two values of the potential energy of the system.
Developing: develop the ability to apply theoretical knowledge when performing laboratory work, the ability to analyze and draw conclusions.
Educational: foster the ability to self-analyze and critical of their knowledge.
Org moment - 5 minutes.
Introduction to the topic of the lesson - 5 minutes.
Study of the theoretical part of the work and design - 10 minutes.
Completion of work - 20 minutes.
Self-assessment of the findings and the final part of the lesson - 5 minutes.
Devices and materials for the lesson.
The definition of potential energy, elastic force is repeated.
Introduction to the topic of the lesson
The teacher briefly talks about the order of the work and the difference from the work described in the textbook.
Recording a lesson topic
1. Writing in a notebook.
Pupils draw up laboratory work and draw a table.
2. The teacher explains the problem using a demonstration, put on a piece of foam on the rod coming from the dynamometer spring, raise the weight by the length of the thread (5-7 cm) and lower the piece of foam against the stopper at the bottom of the dynamometer and rise up when the spring is compressed. And then, according to the work plan, we stretch the spring until the foam plastic touches the limiter of the dynamometer, we measure the maximum tension of the spring and the maximum elastic force.
3. Pupils ask questions, clarify incomprehensible points.
4. Begin to perform the practical part of the work.
5. Perform calculations, check the law of conservation of energy.
6. Draw conclusions, hand over notebooks.
Self-assessment of knowledge
Pupils announce the conclusions, the results obtained and give them an assessment.
Changes to laboratory work were made based on the available equipment.
When performing the work, the set goals are achieved.
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Laboratory work No. 7 "Study of the law of conservation of mechanical energy"
Reshebnik in physics for grade 9 (I.K. Kikoin, A.K. Kikoin, 1999),
task №7
to chapter " LABORATORY WORKS».
Purpose of the work: to compare two quantities - a decrease in the potential energy of a body attached to a spring when it falls and an increase in the potential energy of a stretched spring.
1) a dynamometer, the spring rate of which is 40 N / m; 2) ruler
measuring; 3) load from a set according to mechanics; the mass of the cargo is (0.100 ± 0.002) kg.
Materials: 1) retainer;
2) a tripod with a sleeve and a foot.
For work, the installation shown in Figure 180 is used. It is a dynamometer mounted on a tripod with a lock 1.
The dynamometer spring is terminated with a wire rod with a hook. The latch (on an enlarged scale it is shown separately - marked with the number 2) is a light cork plate (dimensions 5 X 7 X 1.5 mm) cut with a knife to its center. It is placed on the wire rod of the dynamometer. The latch should move along the shaft with little friction, but the friction must still be sufficient so that the latch does not fall down on its own. You need to make sure of this before starting work. For this, the retainer is installed at the lower end of the scale on the limiting bracket. Then they stretch and release.
The detent together with the wire rod should move up, marking the maximum extension of the spring, equal to the distance from the stop to the detent.
If you lift the load hanging on the dynamometer hook so that the spring is not stretched, then the potential energy of the load in relation to, for example, the table surface is mgH. When the load falls (lowering to a distance x = h), the potential energy of the load will decrease by
and the energy of the spring during its deformation increases by
Work order
1. Firmly attach the weight from the mechanics kit to the dynamometer hook.
2. Raise the weight by hand to relieve the spring and place the catch at the bottom of the shackle.
3. Release the load. Falling, the load will stretch the spring. Remove the weight and measure the maximum elongation x of the spring with a ruler according to the position of the retainer.
Presentation on physics for laboratory work No. 2 "Study of the law of conservation of mechanical energy" Grade 10
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Description of the presentation for individual slides:
Laboratory work No. 2 Topic: Study of the law of conservation of mechanical energy. Purpose of the work: to learn how to measure the potential energy of a body raised above the ground and a deformed spring; compare two values of the potential energy of the system. Equipment: tripod with clutch and foot; laboratory dynamometer; ruler; load of mass m on a thread of length l.
Work progress: Note: The difficulty of the experiment lies in the exact determination of the maximum deformation of the spring, since the body moves quickly. P, N h1, m h2, m F, H x, m | ΔEgr |, J Epr, J Epr / | ΔEgr |
Instructions for work: To carry out the work, assemble the installation shown in the figure. The dynamometer is attached to the tripod leg.
1. Tie the weight on the threads to the hook of the dynamometer. Mount the dynamometer in the tripod clamp at such a height that the load raised to the hook does not reach the table when it falls. Measure the weight of the weight P, N. 2. Raise the weight up to the point of the thread attachment. Place the retainer on the dynamometer rod near the restraining bracket. 3. Raise the load almost to the dynamometer hook and measure the height h1, of the load above the table (it is convenient to measure the height at which the lower edge of the load is located).
4. Release the load without jolting. Falling, the weight will stretch the spring, and the retainer will move up the rod. Then, by hand stretching the spring so that the catch is against the limit bracket, measure F, x and h2.
5. Calculate: a) the increase in the potential energy of the spring: Епр = F x / 2; b) a decrease in the potential energy of the cargo: | ΔEgr | = P (h1 - h2). 6. Record the results of measurements and calculations in the table. 7. Make a conclusion: Why is the ratio Епр / | ΔЕгр | can't be equal to 1?
Literature: 1. Textbook: Physics. Grade 10: textbook. for general education. institutions with adj. to the electron. carrier: base and profile. levels / G. Ya. Myakishev, B. B. Bukhovtsev, N. N. Sotsky; ed. V. I. Nikolaeva, N. A. Parfentieva. - M: Enlightenment, 2011. 2.http: //yandex.ru/images 3.http: //mirfiziki.rf lessons
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Laboratory work No. 2 "Study of the law of conservation of mechanical energy" in grade 10.
Textbook: Physics. Grade 10: textbook. for general education. institutions with adj. to the electron. carrier: base and profile. levels / G. Ya. Myakishev, B. B. Bukhovtsev, N. N. Sotsky; ed. V. I. Nikolaeva, N. A. Parfentieva. - M: Enlightenment, 2011.
Description of work: A load of weight P is tied on threads to the hook of the dynamometer spring and, having raised it to a height h1 above the table surface, is released. The height of the load h2 is measured at the moment when the speed of the load becomes equal to 0, as well as the elongation x of the spring at this moment... The decrease in the potential energy of the load and the increase in the potential energy of the spring are calculated.
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Presentation on physics "Study of the law of conservation of mechanical energy" Grade 10
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Selected document for viewing Lab 2.docx
MBOU SOSH r.p. Lazarev Nikolaevsky district Khabarovsk Territory
Completed by: teacher of physics T.A. Knyazeva
Laboratory work No. 2. Grade 10
Study of the law of conservation of mechanical energy.
Objective: learn to measure the potential energy of a body raised above the ground and an elastically deformed spring, to compare two values of the potential energy of the system.
Equipment: a tripod with a coupling and a foot, a laboratory dynamometer with a clamp, a measuring tape, a weight on a thread about 25 cm long.
Determine the weight of the ball F 1 = 1 N.
Distance l from the dynamometer hook to the center of gravity of the ball is 40 cm.
Maximum spring elongation l = 5 cm.
Force F = 20 N, F / 2 = 10 N.
Fall height h = l + l = 40 + 5 = 45cm = 0.45m.
E p1 = F 1 x (l + l) = 1Hx0.45m = 0.45J.
E p2 = F / 2x L = 10Hx0.05m = 0.5J.
The results of measurements and calculations will be entered into the table:
Study of the law of conservation of mechanical energy.
compare the changes in the potential energy of the load and the potential energy of the spring.
tripod with coupling and clamp, dynamometer with fixation, weight, strong thread, measuring tape or ruler with millimeter divisions.
A load of weight P is tied on threads to the hook of the dynamometer spring and, having raised to a height h 1 above the table surface, is released.
Measure the height of the load h 2 at the moment when the speed of the load becomes zero (at the maximum elongation of the spring), as well as the elongation x of the spring at this moment. The potential energy of the load has decreased by
| ΔE gr | = P (h 1 - h 2), and the potential energy of the spring increased by, where k is the coefficient of stiffness of the spring, x is the maximum elongation of the spring corresponding to the lowest position of the load.
Since part of the mechanical energy is transferred to the internal energy due to friction in the dynamometer and air resistance, the ratio
E pr / | ΔE gr | less than one. In this work, it is required to determine how close this ratio is to unity.
The modulus of elasticity and the modulus of elongation are related by the ratio F = kx, therefore, where F is the elastic force corresponding to the maximum elongation of the spring. Thus, to find the ratio E pr / | ΔE gr |, it is necessary to measure P, h 1, h 2, F and x.
To measure F, x and h 2, it is necessary to note the state corresponding to the maximum elongation of the spring. To do this, a piece of cardboard (clamp) is put on the rod of the dynamometer, which can move along the rod with little friction. When the load moves down, the dynamometer restraint bracket will move the retainer, and it will move up the dynamometer rod. Then, stretching the dynamometer by hand so that the retainer is again at the limit bracket, read the value of F, and also measure x and h 2.
Autonomous institution
vocational education
Khanty-Mansiysk Autonomous Okrug - Ugra
"SURGUTSK POLYTECHNICAL COLLEGE"
Kuzmaul Maria Sergeevna, physics teacher
Lesson topic: Laboratory work No. 3 " Study of the law of conservation of mechanical energy ".
Lesson type: laboratory-practical
Techniques: "Log book", explanatory and illustrative, algorithmization.
The purpose of the lesson: study the law of conservation of energy in the course of practical work
Lesson Objectives:
Educational:
teach how to use devices and take readings from devices
teach how to measure the potential energy of a body raised above the ground and a deformed spring; compare two values of the potential energy of the system.
Developing:
development of students' thinking, the formation of them to independently acquire and apply knowledge, observe and explain physical phenomena;
development of the ability to analyze and draw conclusions based on experimental data.
Educational:
encourage students to overcome difficulties in the process of mental activity, encourage tolerance and collectivism;
the formation of a cognitive interest in physics and technology.
Forms of organization learning activities: frontal; individual; group.
Expected result of the lesson:
As a result of educational activities, in a planned lesson, students should:
To consolidate knowledge on the topic "The law of conservation of energy and its application."
Show the skills of individual work, group work;
Improve the previously acquired skills and abilities during the experience through the use of physical devices and measuring instruments to measure physical quantities: friction force, body weight.
To develop the ability to analyze, draw up a report on the work done and draw conclusions based on the result obtained.
UMK: multimedia projector, tripod with clutch and foot; laboratory dynamometer; ruler; load of mass m on a thread of length l, descriptions of laboratory work.
Lesson plan:
1. Organizational moment - 2 minutes(Topic name, goals)
2. Updating - 8 minutes
Checking d / z - frontal survey - 3 min.
What is Potential Energy? Her types?
What is kinetic energy?
What is called total mechanical energy?
What is the law of conservation of mechanical energy?
Reception "Log book" - filling in the column that I know! (Group discussion) - 5min
3. Performing laboratory work - 50 minutes
Conducting safety briefing;
Studying l / r (to acquaint students with devices, pay attention to the order of work).
registration of work by students in notebooks: topic, purpose, equipment, order of work.
students' performance of work, the teacher supervises the work in groups.
Analysis and conclusion on work.
4. Anchoring - 10 min.
Students answer questions individually in writing.
5. Reflection. - 8 minutes
Return to lesson objective: discussion of how frictional force depends on body weight?
Filling in the "logbook".
Questions to groups:
"Who thinks they worked actively in class? Raise your hands."
Do you think you have achieved the correct result?
6. Homework: learn § - 2 minutes.
Laboratory work No. 3 Annex 1.
Topic: Study of the law of conservation of mechanical energy.
Objective: learn to measure the potential energy of a body raised above the ground and a deformed spring; compare two values of the potential energy of the system.
Equipment: tripod with clutch and foot; laboratory dynamometer; ruler; mass weight m on a thread long l.
Theoretical part
The experiment is carried out with a weight attached to one end of a thread of length l... The other end of the thread is tied to the hook of the dynamometer. If the load is lifted, the dynamometer spring becomes undeformed and the dynamometer needle shows zero, while the potential energy of the load is due only to the force of gravity. The load is released and it falls down, stretching the spring. If for the zero level of reference of the potential energy of the interaction of a body with the Earth we take the lower point, which it reaches during the fall, then it is obvious that the potential energy of the body in the field of gravity is converted into the potential energy of deformation of the dynamometer spring:
mg (l + Δl) = kΔl 2
/2
, where Δl- maximum elongation of the spring, k- its rigidity.
The difficulty of the experiment lies in accurately determining the maximum deformation of the spring, since the body moves quickly.
Directions for work
To perform the work, assemble the installation shown in the figure. The dynamometer is attached to the tripod leg.
1. Tie the weight to the thread, tie the other end of the thread to the hook of the dynamometer and measure the weight of the weight F T = mg(v in this case the weight of the load is equal to its gravity).
2. Measure the length l the thread on which the load is tied.
3. Raise the load to point 0 (marked on the dynamometer).
4. Release the load, measure the maximum elastic force with a dynamometer F ynp and a ruler maximum spring tension Δl, counting it from the zero division of the dynamometer.
5. Calculate the height from which the load falls: h = l + Δl(this is the height by which the center of gravity of the load is shifted).
6. Calculate the potential energy of the lifted load E " P = mg (l + Δl).
7. Calculate the energy of the deformed spring E " P = kΔl 2 /2, where k = F control / Δl
Substituting the expression for k into the formula for energy E " P get E " P =; F control Δl / 2
8. Enter the results of measurements and calculations in the table.
| F T = mg | F control | h = l + Δl | E " P = mg (l + Δl) | E " P = F control Δl / 2 |
||
9. Compare the values of energies E " P and E " P... Think about why the values of these energies do not coincide exactly.
10. Make a conclusion about the work done.
Tasks
Educational:
· To form knowledge, abilities, skills on the topic “Work of power. Conservation laws in mechanics "
· To generalize and systematize the knowledge of students on the topic “Work of power. Conservation laws in mechanics "
· Carry out preparation for the final certification, in the course of repeating previously studied topics
Educational:
To foster independence through the organization of independent work in the classroom
To foster the desire to master knowledge, to search interesting facts
To educate attentiveness, accuracy
Developing:
To form students' assessment skills, a critical attitude to the level of their training through self-examination of the tasks performed in the lesson
To develop the ability to select the necessary knowledge from a large amount of information, the ability to generalize facts, draw conclusions (draw up a synopsis on the previous topic, which reflects all the concepts, phenomena and laws of this section and their relationship)
Improve the skills of independent work (independent problem solving)
Main subtopics
Structural and logical analysis of the topic
Main subtopics.
Law of energy conservation
Section 43. Work of power
Section 44. Power
Section 45. Energy
§ 46. Kinetic energy and its change
Section 47. Work of gravity
§ 48. Work of elastic force
§ 49. Potential energy
§ 50. The law of conservation of energy in mechanics
§ 51. Reduction of the mechanical energy of the system under the action of friction forces
Thematic planning basic and specialized level
in physics grade 10 (2h / week and 5h / week)
In this topic, the following formulas are introduced:
Here A is the work, F is the modulus of the force performing the work, S is the modulus of displacement, α is the angle between the vectors of force and displacement, k is stiffness, x is deformation, N is power, v is speed, t is time.
In the formulas, a certain body performs work or develops power, which acts on a given body with a certain force F. This can be a traction force or a tension force or a friction force, etc., but not a resultant of all the forces acting on a given body.
When studying the topic “Work of power. Conservation laws in mechanics "are introduced as follows concepts:
Physical concepts: Mechanical work, power, energy, kinetic energy, potential energy, work of gravity, work of elastic force, absolutely elastic impact, absolutely inelastic impact.
The laws: the law of conservation of momentum, the law of conservation of energy.
Frontal laboratory work
Study of the law of conservation of mechanical energy
Objective: learn to measure the potential energy of a body raised above the ground and a deformed spring, compare two values of the potential energy of the system.
Equipment: a tripod with a clutch and a foot, a laboratory dynamometer, a ruler, a load of mass m on a thread of length l, a set of cardboard boxes about 2 mm thick, paint and a brush.
Task
The driver turned off the engine at the moment when the car's speed was. After ∆t = 2 s, the car's speed dropped to What was the momentum of the car at the moment the engine was turned off? What is the change in the momentum of the vehicle ∆p? What is the impulse of the force of resistance to the movement of the car? The force of resistance to movement during the time ∆t was constant and is
According to the basic equation of dynamics, the impulse of the force acting on the body is equal to the change in the impulse of this body, which means that ∆p =.
The change in impulse ∆p is equal to the difference between the final p impulse and the initial one. By definition of momentum and, where m is the mass of the car.
Let us take into account that the change in impulse ∆p is less than zero, because the final speed is less than the initial one. Then -∆p = -, whence the mass of the car
Now we will find the initial impulse of the car
Substituting the data into the equations, we get:
∆p = = 1.2 N ∙ s,
Answer:∆p = = 1.2 N ∙ s, kg
Qualitative task:
Why does a cyclist increase his speed when approaching an incline?
If there is no friction, then the kinetic energy during the ascent of the cyclist turns into potential, and the speed must first be increased so that the kinetic energy is sufficient for the ascent to the upper point (the total energy remains constant).
If the kinetic energy does not decrease, this means that someone is sure to do the work, and this compensates for the loss of kinetic energy. In this problem, the work must of course be done by a cyclist, i.e. when climbing uphill, the cyclist pedals so hard that the work he does exactly compensates for the loss of kinetic energy. If you use formulas, then you need to use the mechanical energy theorem; the final mechanical energy, minus the initial mechanical energy is equal to the work of the external non-conservative forces, plus the work of the friction force (if any). Only when the cyclist performs pedaling work during the ascent, the kinetic energy can remain constant.
Used methodological literature:
Kamenetsky “theory and methods of teaching physics at school. Private questions. "
Myakishev grade 11
Kasatkina "Physics Tutor"
Popular non-fiction literature and Internet resources recommended for students:
Kvant magazine
Potential Magazine
Physics for schoolchildren magazine
Appendix
Concepts
Mechanical work Is a physical quantity equal to the product of the modules of force and displacement by the cosine of the angle between them.
Power- a physical quantity equal to the ratio of work to the period of time during which it was performed.
Energy- a physical quantity, which is a quantitative measure of the movement and interaction of all types of matter. It is equal to the work that a body or a system of bodies can perform during the transition from this state to the zero level.
Kinetic energy- the energy that the body possesses due to its movement.
Potential energy- energy due to the interaction of various bodies or parts of one body. Depends on the relative position of the bodies or the amount of deformation of the body.
Work of gravity- does not depend on the trajectory of the body and is always equal to the change in the potential energy of the body, taken with the opposite sign.
Elastic force work- is equal to the change in potential energy, taken with the opposite sign.
Absolutely resilient impact- collision, in which the mechanical energy of the system of bodies is conserved.
Absolutely inelastic blow- such impact interaction, in which the bodies are connected (stick together) with each other and move on as one body.
Selected document for viewing Lab 2.docx
MBOU SOSH r.p. Lazarev Nikolaevsky district Khabarovsk Territory
Completed by: teacher of physics T.A. Knyazeva
Laboratory work No. 2. Grade 10
Study of the law of conservation of mechanical energy.
Objective: learn to measure the potential energy of a body raised above the ground and an elastically deformed spring, to compare two values of the potential energy of the system.
Equipment: a tripod with a coupling and a foot, a laboratory dynamometer with a clamp, a measuring tape, a weight on a thread about 25 cm long.
Determine the weight of the ball F 1 = 1 N.
Distance l from the dynamometer hook to the center of gravity of the ball is 40 cm.
Maximum spring elongation l = 5 cm.
Force F = 20 N, F / 2 = 10 N.
Fall height h = l + l = 40 + 5 = 45cm = 0.45m.
E p1 = F 1 x (l + l) = 1Hx0.45m = 0.45J.
E p2 = F / 2x L = 10Hx0.05m = 0.5J.
The results of measurements and calculations will be entered into the table:
Laboratory work "Study of the law of conservation of mechanical energy"
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STUDYING THE LAW OF CONSERVATION OF MECHANICAL ENERGY
Objective: to establish experimentally that the total mechanical energy of a closed system remains unchanged if only the forces of gravity and elasticity act between the bodies.
Equipment: a device for demonstrating the independence of the action of forces; scales, weights, measuring ruler; plumb line; white and carbon paper; tripod for frontal work.
The setup for the experiment is shown in the figure. When the rod A deviates from the vertical position, the ball at its end will rise to a certain height h relative to the initial level. In this case, the system of interacting bodies "Earth-ball" acquires an additional supply of potential energy ? E p = mgh .
If the rod is released, it will return to the vertical position, where it will be stopped by a special stop. Assuming the friction force is very small, it can be assumed that during the movement of the rod, only gravitational and elastic forces act on the ball. Based on the law of conservation of mechanical energy, it can be expected that the kinetic energy of the ball at the moment of passing the initial position will be equal to the change in its potential energy: 
Having calculated the kinetic energy of the sphere and the change in its potential energy, and comparing the results obtained, it is possible to experimentally verify the law of conservation of mechanical energy. To calculate the change in the potential energy of the ball, you need to determine its mass m on the scales and measure the height h of the ball rise with a ruler.
To determine the kinetic energy of the ball, it is necessary to measure its velocity modulus?. To do this, the device is fixed above the table surface, the rod with the ball is pulled aside to the height H + h and then released. When the rod hits the stop, the ball jumps off the rod.
The speed of the ball changes during the fall, but the horizontal component of the speed remains unchanged and equal in magnitude to the speed? ball at the moment the rod hits the stop. So the speed? the ball at the moment of breaking off the rod can be determined from the expression
V = l / t, where l is the range of the ball, t is the time of its fall.
The time t of free fall from a height H (see Fig. 1) is equal to:, therefore
V = l / v 2H / g. Knowing the mass of the ball, you can find its kinetic energy: E k = mv 2/2 and compare it with the potential energy.
Work order
1. Mount the device in a tripod at a height of 20-30 cm above the table, as shown in the figure. Place the ball with the hole on the rod and do a preliminary experiment. At the place of the fall
ball, tape a piece of white paper with duct tape and cover it with a sheet of carbon paper.
3. Putting the ball on the rod again, move the rod to the side, measure the height of the ball rise h in relation to the initial level and release the rod. Having removed a sheet of carbon paper, determine the distance l between the point on the table under the ball in its initial position, found by the plumb line, and the mark on the sheet of paper at the point where the ball falls.
4. Measure the height of the ball above the table in the starting position. Weigh the ball and calculate the change in its potential energy? E p and kinetic energy Ek at the moment the ball passes the equilibrium position.
5. Repeat the experiment with two other values of the height h and make measurements and calculations. Enter the results in the table.
7. Compare the values of changes in the potential energy of the ball with its kinetic energy and draw a conclusion about the results of your experiment
Reshebnik in physics for grade 9 (I.K. Kikoin, A.K. Kikoin, 1999),
task №7
to chapter " LABORATORY WORKS».
measuring; 3) load from a set according to mechanics; the mass of the cargo is (0.100 ± 0.002) kg.
Materials: 1) retainer;
2) a tripod with a sleeve and a foot.
and the energy of the spring during its deformation increases by
Work order
Laboratory work No. 7 "Study of the law of conservation of mechanical energy"
LABORATORY WORKS> number 7
Purpose of the work: to compare two quantities - a decrease in the potential energy of a body attached to a spring when it falls and an increase in the potential energy of a stretched spring.
1) a dynamometer, the spring rate of which is 40 N / m; 2) ruler
Measuring; 3) load from a set according to mechanics; the mass of the cargo is (0.100 ± 0.002) kg.
Materials: 1) retainer;
2) a tripod with a sleeve and a foot.
For work, the installation shown in Figure 180 is used. It is a dynamometer mounted on a tripod with a lock 1.
The dynamometer spring is terminated with a wire rod with a hook. The latch (on an enlarged scale it is shown separately - marked with the number 2) is a light cork plate (dimensions 5 X 7 X 1.5 mm) cut with a knife to its center. It is placed on the wire rod of the dynamometer. The latch should move along the shaft with little friction, but the friction must still be sufficient so that the latch does not fall down on its own. You need to make sure of this before starting work. For this, the retainer is installed at the lower end of the scale on the limiting bracket. Then they stretch and release.
The detent together with the wire rod should move up, marking the maximum extension of the spring, equal to the distance from the stop to the detent.
If you lift the load hanging on the dynamometer hook so that the spring is not stretched, then the potential energy of the load in relation to, for example, the table surface is mgH. When the load falls (lowering to a distance x = h), the potential energy of the load will decrease by
And the energy of the spring during its deformation increases by
Work order
1. Firmly attach the weight from the mechanics kit to the dynamometer hook.
2. Raise the weight by hand to relieve the spring and place the catch at the bottom of the shackle.
3. Release the load. Falling, the load will stretch the spring. Remove the weight and measure the maximum elongation x of the spring with a ruler according to the position of the retainer.
4. Repeat the experiment five times.
6. Enter the results in the table:
7. Compare attitude
With the unit and draw a conclusion about the error with which the law of conservation of energy was verified.
The law of conservation of mechanical energy. The total mechanical energy of a closed system of bodies interacting with gravitational forces or elastic forces remains unchanged for any motions of the bodies of the system
Consider such a body (in our case, a lever). Two forces act on it: the weight of the loads P and the force F (elasticity of the dynamometer spring), so that the lever is in equilibrium and the moments of these forces must be equal in modulus to their honey. We define the absolute values of the moments of forces F and P, respectively:
Consider a weight attached to an elastic spring as shown in the figure. First, we hold the body in position 1, the spring is not tensioned and the elastic force acting on the body is zero. Then we release the body and it falls under the action of gravity to position 2, in which the force of gravity is fully compensated by the elastic force of the spring when it is lengthened by h (the body is at rest at this moment in time).
Let us consider the change in the potential energy of the system when the body moves from position 1 to position 2. When moving from position 1 to position 2, the potential energy of the body decreases by mgh, and the potential energy of the spring increases by
The aim of the work is to compare these two values. Measuring instruments: a dynamometer with a predetermined spring rate of 40 N / m, a ruler, a weight from a set according to mechanics.
Laboratory work 5. Study of the law of conservation of mechanical energy
1. Assemble the installation shown in the figure.
2. Tie the weight on the threads to the hook of the dynamometer (thread length 12-15 cm). Mount the dynamometer in the tripod clamp at such a height that the load raised to the hook does not reach the table when it falls.
3. After lifting the weight so that the thread is slack, place the stopper on the dynamometer rod near the restraining bracket.
4. Raise the load almost to the hook of the dynamometer and measure the height of the load above the table (it is convenient to measure the height at which the lower edge of the load is located).
9. Compare this ratio with one and write the conclusion in your laboratory notebook; indicate what transformations of energy occurred during the downward movement of the load.
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Ufa State Aviation Technical University
Laboratory work No. 13
(in physics)
Study of the law of conservation of mechanical energy
Faculty: IRT
Group: T28-120
Completed by: V. V. Dymov
Checked:
1. Purpose of work: Study of the law of conservation of mechanical energy and verification of its validity using Maxwell's pendulum.
2. Devices and accessories: Maxwell's pendulum.
Replaced rings
Millisecond watch
Base
Adjustable feet
Column, millimeter scale
Fixed bottom bracket
Movable bracket
Electromagnet
Photoelectric sensor No. 1
Collar for adjusting the length of the bifilar suspension of the pendulum
Photoelectric sensor No. 2
3. Table with the results of measurements and calculations
3.1 Measurement results
|
t, sec |
m, kg |
h max , m |
t cp , With |
J, kg * m 2 |
a, m / s 2 |
|
t 1 =2,185 t 2 =3,163 t 3 =2,167 |
m d =0,124 m O =0,033 m To =0,258 |
h max =0,4025 |
t Wed =2,1717 t Wed = 2.171 ± 0.008 |
J = 7.368 * 10 -4 |
a= 0,1707 a =0.1707 ± 0.001 |
3.2 Test results
|
№ experience |
t, sec |
h, m |
E n , J |
E n , J |
E k , J |
E k , J |
|
t’=1,55 |
h’=0,205 |
E n ’=0,8337 |
E n ’=2,8138*10 -2 |
E k ’= 1,288 |
||
|
t’’= 0 |
h’’=0,4025 |
E n ’’= 2,121 6 |
E k ’’= 0 |
|||
|
t’ ’ ’=2,1717 |
h’ ’ ’=0 |
E n ’’’=0 |
E k ’’ ’ = 2,12 19 |
4. Calculation of measurement results and errors
4.1. Direct measurement of the time of full fall of the pendulum
t 1 = 2.185c.
t 2 = 3.163c.
t 3 = 2.167c.
4.2. Calculation of the mean time to full fall
4.3. Calculation of the acceleration of the translational movement of the pendulum
l= 0.465m - thread length
R= 0.0525m- ring radius
h= l- R-0.01m = 0.4025m- path when the pendulum falls
4.4. Calculation of the height of the position of the pendulum at the moment of time t’
;
;
;
v’ - the speed of translational motion at the moment of time t’
- the speed of the rotational movement of the pendulum axis at the moment of time t’
r= 0.0045m- radius of the pendulum axis
4.5. Calculation of the moment of inertia of a pendulum
J 0 – moment of inertia of the pendulum axis
m 0 = 0.033kg – pendulum axis mass
D 0
=
–
axle diameter
pendulum
J d – disk moment of inertia
m d = 0.124kg – disk mass
D d =
–
disc diameter
J To – moment of inertia of the trim ring
m To = 0.258kg – weight of the attachment ring
D To = 0.11m - diameter of the attachment ring
4.6. Calculation of the potential energy of the pendulum relative to the axis passing along the axis
pendulum, at position at the moment of time t’
4.7. Calculation of the kinetic energy of the pendulum at the moment of time t’
- kinetic energy of translational motion
- kinetic energy of rotational motion
4.8. Calculation of the error of direct measurements
4.9. Calculation of indirect measurement errors
5. End results:
The total mechanical energy of the pendulum at some point in time is equal to E= E n + E k
For experiment # 1: E’= E n ’+ E k '= 0.8337J + 1.288J = 2.1217J
For experiment number 2: E’’= E n ’’+ E k '' = 2.1216J + 0 = 2.1216J
For experiment number 3: E’’’= E n ’’’+ E k '' '' = 0 + 2.1219J = 2.1219J
From these experiments it follows that 
(difference in 10
-3
J due to the imperfection of measuring instruments), therefore, the law of conservation of total mechanical energy is correct.