Beijing Normal University Ninth Grade Physics Volume 1

Description

"Mechanical Energy" Mechanical energy, internal energy and their transformation PPT courseware 2

Knowledge review

1. What form of mechanical energy does each of the following objects have?

(1) Football rolling on the ground

(2) A stone on the top of a mountain

(3) A bow bent on the ground

(4) Planes flying forward in the sky

2. Regarding the concept of energy, which of the following statements is correct ( )

A. Objects with equal potential energy must be at the same height

B. Since the hanging object does no work, it cannot

C. Bullets flying in the air have the ability to do work, so they have the ability to

D. If an object has mechanical energy, then the object must have both kinetic energy and potential energy.

3. When a bicycle goes downhill, its speed will increase without pedaling. During this process, the kinetic energy of the bicycle gradually ________, and the gravitational potential energy of the bicycle gradually ________.

4. An aircraft flies horizontally and at a constant speed over the disaster area and continuously drops relief supplies to the disaster area. During this process, the aircraft's kinetic energy _____ and gravitational potential energy ____ (fill in "get bigger" or "get smaller")

5. After the hydrogen balloon is released, if its movement can be seen as rising at a constant speed, then the hydrogen balloon will

The kinetic energy of ________(increases/changes/decreases),

Gravitational potential energy ________(increase/change/decrease),

Mechanical energy ________(increase/change/decrease)

Kinetic energy and potential energy can be converted into each other

Example 1: Observe the movement of a pendulum

When the pendulum ball swings downward from point A, its speed becomes larger and larger, its kinetic energy gradually ____, and its potential energy gradually _____

When the pendulum ball reaches the lowest point O’: its kinetic energy is the most___ and its potential energy is the most___

From A to O’: The potential energy of the pendulum ball gradually transforms into ___ energy.

After that, the pendulum ball moves to the other side of OO/. As the pendulum ball rises, its speed becomes more and more ____, and the kinetic energy is gradually converted into ____ energy.

When the pendulum ball reaches the highest point B, its kinetic energy is ____ and its potential energy is ____.

Example 2: Roll

____ ability gradually transforms into ____ ability.

When falling: gravitational potential energy - kinetic energy

____ ability gradually transforms into ____ ability.

When rising: kinetic energy - gravitational potential energy

Example 3: Roller coaster

From the highest point to the lowest point: ______ energy gradually transforms into ______ energy.

From the lowest point to the highest point: ______ energy gradually transforms into ______ energy.

Practice in class

1. Shown is the design plan of a light rail station on Shanghai's "Pearl Line". The track connected to the platform has a certain slope. Please analyze the advantages of this design from the perspective of energy saving.

This method can make the train go uphill when entering the station, converting kinetic energy into potential energy, and the speed decreases; when leaving the station, go downhill, convert potential energy into kinetic energy, and increase the speed, thereby saving energy.

2. Spread a piece of paper on the level ground and paint the surface of the ball black so that when it falls freely from different heights, it will leave black round spots A and B on the paper. The circles formed by the ball falling from a higher place Which one is the spot shown in the picture? What is the basis for your judgment?

The ball has greater gravitational potential energy at a higher place. During the falling process, the gravitational potential energy is converted into kinetic energy. The ball has greater kinetic energy before it touches the ground. During the contact with the ground, the kinetic energy is converted into elastic potential energy. Therefore, the deformation of the ball is larger, and the circular spots formed on the ground are larger.

3. As shown in the figure, when the object a placed at the top of the inclined plane slides to the three positions b, c, and d along three different paths ab, ac, and ad, respectively, if friction and air resistance are not considered, compare their kinetic energies. Size, the correct one is ( )

A. The kinetic energy of point b is large

B. The kinetic energy of point c is large

C. The kinetic energy at point d is large

D. The kinetic energy of the three points is the same

4. The picture shows the scene of a diver diving from a springboard. From the moment the athlete jumps into the air and moves upwards and then falls downwards into the water, if air resistance is not taken into account, during the whole process ( )

A. The athlete's kinetic energy keeps increasing, but the mechanical energy remains unchanged.

B. The athlete's gravitational potential energy has been decreasing, and the mechanical energy has decreased.

C. The athlete's kinetic energy first decreases and then increases, while the mechanical energy remains unchanged.

D. The athlete's gravitational potential energy first decreases and then increases, and the mechanical energy increases.

5. Figure 6 shows the scene of playing with a slingshot. Experience shows that the longer the rubber band is stretched, the farther the same "bullet" shoots, which shows that the elastic potential energy of the rubber band is related to ___________;

If the rubber bands are stretched to the same length but the masses of the "bullets" used are different, then the "bullet" with greater mass will be ejected from a smaller distance because the "bullet" with greater mass will have a smaller ______ when ejected.

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For more information about the PPT courseware "Mechanical Energy, Mechanical Energy, Internal Energy and Its Transformation", please click on the Mechanical Energy ppt, Mechanical Energy, Internal Energy and its Transformation ppt tag.

"Mechanical Energy" PPT (second lesson):

"Mechanical Energy" PPT (Lesson 2) Part One: Teaching Objectives 1. Know that kinetic energy and potential energy can be converted into each other. 2. Know that mechanical energy is conserved... Mechanical energy PPT, part 2 content: Classroom experiment Experiment 1: Simple pendulum experiment divided into small...

"Mechanical Energy" PPT (first lesson):

"Mechanical Energy" PPT Part One Content: Teaching Objectives 1. Know the concept of kinetic energy and understand the two factors that affect the size of kinetic energy. 2. Know the concept of potential energy and understand the factors that affect the magnitude of gravitational potential energy and elastic potential energy. 3. Understand the concept of mechanical energy. 4. Take advantage of the machine..

"Understanding Kinetic Energy and Potential Energy" Mechanical Work and Mechanical Energy PPT Courseware 2:

"Understanding Kinetic Energy and Potential Energy" Mechanical Work and Mechanical Energy PPT Courseware 2 1: What is energy? (a) A stretched bow can shoot out arrows (b) Waves hit the surfboard (c) The deformed springboard bounces the athlete up (d) The diver falls into the water and splashes 1. Objects can do things to the outside world..

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Update Time: 2024-07-03

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