"Internal Energy" Mechanical energy, internal energy and their transformation PPT courseware 6

Description

"Internal Energy" Mechanical energy, internal energy and their transformation PPT courseware 6

teaching objectives

1. Know the molecular kinetic theory.

2. Know the concept and units of internal energy.

3. Understand the relationship between internal energy and temperature, and know the two methods of changing internal energy.

1. Basic image of material structure

1. Matter is composed of a large number of molecules

2. Molecules are constantly moving irregularly

Summarize the phenomenon:

Solids, liquids, and gases all have this phenomenon: when different substances come into contact with each other, they will enter each other. In physics, this phenomenon is called diffusion.

Think: What does the diffusion phenomenon indicate?

Conclusion 1: The molecules of all objects are constantly moving irregularly.

Observe and think

What did you see?

What does this phenomenon indicate?

Conclusion 2: The higher the temperature, the more intense the molecular motion.

3. There are interactions between molecules

Common substances are composed of a large number of molecules. The molecules are constantly moving irregularly. There are attraction and repulsion forces between the molecules.

2. Characteristics of solids, liquids and gases

3. Internal energy of an object

We know that when half a cup of hot water is poured into half a cup of cold water, it becomes a cup of warm water. This is because the hot water loses an energy and the cold water gains an energy. From the perspective that objects are composed of molecules, what exactly is this? What form of energy is it?

Observe and compare:

①The moving basketball has kinetic energy, but what about the moving molecules?

Conclusion: Moving molecules also have kinetic energy.

②The apple and the earth attract each other with potential energy

Do molecules that attract each other also have potential energy?

Conclusion: Molecules that attract each other have potential energy

③ Each part of the compressed spring repels each other and has potential energy.

Discussion: Is there potential energy between molecules that repel each other?

Conclusion: Molecules that repel each other also have potential energy. Because there are interactions between molecules, there is potential energy between molecules.

Internal energy

1. Definition: The sum of the kinetic energy and molecular potential energy of a large number of molecules in an object undergoing thermal motion.

2. Thermal motion: the irregular motion of a large number of molecules inside an object.

3. The relationship between thermal motion and internal energy: the higher the temperature of the object, the more intense the thermal motion of the molecules, and the greater the internal energy.

Do the following two objects have internal energy?

The temperature is very high, the molecules move fiercely, and it has internal energy.

Although the temperature is low, the internal molecules are still moving irregularly, and it also has internal energy.

Conclusion: Any object has internal energy. Because the molecules in the object are constantly moving irregularly.

think about it

1. What happens to the internal energy of an object when its temperature increases or decreases?

As the temperature of an object increases, the internal energy increases. As the temperature of an object decreases, the internal energy decreases.

2. What is the difference between internal energy and mechanical energy?

Internal energy is energy related to microscopic motion and related to changes in temperature;

Mechanical energy is energy related to macroscopic motion, and is related to the speed and height of motion.

3. A small glass of water and a large bucket of water have the same temperature. Do they have the same internal energy? If different, which one has greater internal energy? What does it mean?

Different, there can be more in a bucket of water. It shows that the internal energy of an object is also related to the number of molecules.

How to change internal energy

Your hands get cold in winter, how do you usually keep them warm?

Both of the above methods can increase the internal energy of the hand.

①Heat transfer changes internal energy

Heat transfer can change the internal energy of an object

High-temperature objects release heat and their internal energy decreases; low-temperature objects absorb heat and their internal energy increases.

②Work changes internal energy

What examples do the ancients use to drill wood to make fire have the same principle?

Energy transformation: mechanical energy → internal energy;

Temperature changes: all are warming;

Whether to do work: to overcome friction and do work.

Doing work can change internal energy

Scientific inquiry: Doing work changes the internal energy of an object

Experiment 1, as shown in the picture, inject a small amount of ether into the thin-walled metal cylinder, plug it in, and wrap a rope around the outer wall of the metal cylinder 1-2 times. Then press the arrow in the picture

Pull the rope back and forth in the direction.

(1) What happened:

The rubber stopper will pop up and white mist will appear.

(2) In the process of pulling the rope back and forth, is there any work done?

Work against friction

(3) How is energy transformed?

mechanical energy→internal energy

(4) What changes happen to ether?

The internal energy increases, the temperature rises, and the ether vaporizes.

(5) What is the reason for the increase in internal energy of ether?

When the outside world does work on an object, the internal energy of the object increases.

Experiment 2, compression ignition nitrocellulose

(1) Why choose nitrocellulose?

Because nitrocellulose contains ether, ether has a low ignition point and is flammable.

(2) When depressing the piston, is there any work done? Who does work on whom in the device?

Work is done, the piston does work on the air

(3) How is energy transformed?

Mechanical energy → Internal energy The internal energy of the air in the cylinder increases and the temperature rises.

(4) What causes cotton to burn?

Reaching the ignition point of ether

(5) How to increase the internal energy of air?

When work is done on the air, the internal energy of the air increases

Summary of this lesson

1.Definition of internal energy

The sum of the kinetic energy and potential energy of all molecules inside an object is called the internal energy of the object.

2. Methods of changing internal energy

(1) Heat transfer (2) Work

3. Law of conservation of energy

Energy neither disappears nor is created out of thin air. It only transforms from one form to another, or transfers from one object to another. In the process of transformation and transfer, the total amount of energy constant.

Class exercises

1. The ways to change the internal energy of an object are _______ and _____.

2. The sum of __________________ and _________ inside an object is called the internal energy of the object. As the temperature of the object increases, the internal energy of the object ______.

3. In winter, breathing into your hands with your mouth will warm your hands. This is a ______ method to increase the internal energy of your hands. Rubbing your hands can also warm your hands. This is a ____ method to increase the internal energy of your hands. .

4.Judgement questions:

A The internal energy of ice at 0°C is zero ( )

B An object with zero mechanical energy must have zero internal energy ( )

C As the temperature of an object increases, the internal energy must increase ( )

D An object with a high temperature must have a large internal energy ( )

E When an object absorbs heat, its internal energy must increase ( )

5. The following process is the conversion of internal energy into mechanical energy ( )

A Use the grinding wheel to sharpen the knife. B The gas stove boils water and the water temperature rises.

C The rocket soars into the sky D The meteorite falls into the atmosphere and becomes a meteor

6. Point out how most of the energy is converted in the following phenomena?

When an electric fan works, ____ energy is converted into ______ energy

A lit candle’s ______ energy is converted into ____ energy

Rubbing your hands together ______ energy is converted into ____ energy

Incandescent lamps emit light that converts ____ energy into _____ energy

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

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Update Time: 2024-12-01

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