"Law of Conservation of Mechanical Energy" PPT quality courseware

Description

"Law of Conservation of Mechanical Energy" PPT quality courseware

Part One: Core Competency Goals

physical concepts

Know that energy conservation is an important law of nature, know what mechanical energy is, and understand the content and conditions of the law of conservation of mechanical energy.

scientific thinking

Understand the method of analyzing problems from the perspective of conservation, be able to judge whether mechanical energy is conserved based on the conditions for the conservation of mechanical energy, and be able to use the law of conservation of mechanical energy to solve related problems.

Scientific attitude and responsibility

Understand the impact of the law of conservation of mechanical energy on daily life, and appreciate the role of conservation ideas in promoting physics.

Law of conservation of mechanical energy PPT, part 2 content: pre-class learning

Knowledge point 1: Pursuing conserved quantities

Knowledge point 2: Mutual conversion of kinetic energy and potential energy

[Viewing pictures to help students]

In the above three scenarios, what are the energy transformations of children, pole vaulters, and divers?

1. Gravitational potential energy and kinetic energy: When only gravity does work, if gravity does positive work on the object, the object's gravitational potential energy ________, kinetic energy _______, and _____________ are converted into kinetic energy; if gravity does negative work, then _______ is converted into kinetic energy. for_____________.

2. Elastic potential energy and kinetic energy: When only the elastic force of the spring does work, if the elastic force does positive work, then the elastic potential energy of the spring _______, and the kinetic energy of the object _______, _____________ is converted into kinetic energy.

3. Mechanical energy

(1)Definition: ______________, elastic potential energy and _______ are all forms of energy in mechanical motion, collectively referred to as mechanical energy.

(2) Change of mechanical energy: Mechanical energy can be converted from one form to another through work done by _______ or elastic force.

[Thinking and Judging]

(1) Through work done by gravity, kinetic energy and gravitational potential energy can be converted into each other. ( )

(2) Through elastic force doing work, kinetic energy and elastic potential energy can be converted into each other. ( )

(3) The mechanical energy of the object must be positive. ( )

(4) Mechanical energy can be converted into other energy through work done by gravity or elastic force. ( )

Knowledge point three: Law of conservation of mechanical energy

1. Law of conservation of mechanical energy

In an object system where only _______ or _______ do work, kinetic energy and potential energy can be converted into each other, and the total mechanical energy ______________.

2. Expression: Ek2+Ep2=Ek1+Ep1.

3. Mechanical energy conservation condition: Only _______ or elastic force does work.

[Thinking and Judging]

(1) The mechanical energy of an object moving in a straight line at a uniform speed must be conserved. ( )

(2) The mechanical energy of an object moving at variable speeds may be conserved. ( )

(3) When the work done by the external force on the object is zero, mechanical energy must be conserved. ( )

(4) When mechanical energy is conserved, the object may experience resistance. ( )

(5) The external force on the object is not equal to zero, and its mechanical energy is definitely not conserved. ( )

(6) When the speed of an object increases, its mechanical energy may decrease. ( )

Law of Conservation of Mechanical Energy PPT, Part 3: Core Research

Core Point 1: Understanding and Judgment of Mechanical Energy Conservation Conditions

1. Research objects

(1) When only gravity does work, an object (actually a system composed of the object and the earth) can be taken as the research object.

(2) When the elastic force between objects does work, the system composed of these objects must be taken as the research object (making these elastic forces become the internal forces of the system).

2. Understanding conservation conditions

(1) From the analysis of energy conversion, only the mutual conversion of kinetic energy and potential energy occurs inside the system, and there is no conversion between other forms of energy (such as internal energy). The mechanical energy of the system is conserved.

(2) From the analysis of work conditions, the condition for conservation of mechanical energy is

It can be understood from the following three situations:

① Only affected by gravity: such as various projectile motions (free fall, vertical upward throw, horizontal throw, oblique throw, etc.) without considering air resistance.

②Subject to other forces, but other forces do not do work, only gravity or elasticity does work. For example: an object slides along a smooth curved surface, affected by gravity and the supporting force of the curved surface, but the supporting force of the curved surface does no work on the object.

③There are systematic internal forces doing work, but the algebraic sum of the work done is zero.

[Examination Cases]

[Example 1] (Multiple choice) As shown in the figure, in the following situations, the mechanical energy of the system is conserved ()

A. In picture A, a projectile moves in a complex curve in a smooth bowl.

B. In Picture B, the athlete jumps higher and higher on the trampoline.

C. In Figure C, a wooden block is placed on the trolley, and the left side of the trolley is connected to the wall by a spring. When the car moves left and right, the wooden block does not slide relative to the car (the friction between the wheels and the ground is not counted)

D. In Figure C, if the car moves, the wooden block slides relative to the car.

Summary of methods Methods for judging conservation of mechanical energy

(1) Work analysis method (commonly used for single objects)

(2) Energy analysis method (commonly used in systems composed of multiple objects)

[For training 2] (Multiple choice) As shown in the picture, an inclined plane is placed on a smooth horizontal surface, and a small object slides freely from the top of the inclined plane without friction. During the sliding process ()

A. The work done by the slope on the elastic force of the small object is zero.

B. The gravitational potential energy of small objects is completely converted into the kinetic energy of small objects

C. The mechanical energy of small objects is not conserved

D. Conservation of mechanical energy in the system composed of small objects, inclined planes and the earth

Core Point 2 Application of the Law of Conservation of Mechanical Energy

[Problem exploration]

As shown in the figure, a small ball of mass m slides down from a smooth surface. When it reaches position A with a height of h1, the velocity is v1. When it slides to position B with a height of h2, the velocity is v2. In the process of sliding from height h1 to height h2 (not counting air resistance):

(1) How much has the ball’s gravitational potential energy been reduced?

(2) How much has the ball’s kinetic energy increased?

(3) Is the mechanical energy conserved during the ball's descent? If conserved, list the expression.

(4) Is the decrease in gravitational potential energy of the ball equal to the increase in kinetic energy?

Core Point Three: Mechanical Energy Conservation of Non-Particle Objects

1. When applying the law of conservation of mechanical energy to deal with practical problems, we often encounter objects such as "chains" and "liquid columns". They will deform during the movement and their center of gravity relative to the object will also change. Therefore, such objects cannot Then treat it as a particle.

2. Although the object cannot be treated as a particle, because only gravity does work, the overall mechanical energy of the object is conserved. In general, the object can be processed in segments, the center of gravity position of each part of the regular object with uniform mass distribution can be determined, and the solution can be solved based on the changes in the gravitational potential energy of the object in the initial and final states.

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Update Time: 2024-09-16

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