"Internal Energy of Objects" Internal Energy and Heat Engine PPT Courseware 3

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"Internal Energy of Objects" Internal Energy and Heat Engine PPT Courseware 3

Knowledge review

The concept of kinetic energy and potential energy

The energy an object possesses due to motion is called kinetic energy;

The energy an object has due to being lifted up is called gravitational potential energy

The energy an object possesses due to elastic deformation is called elastic potential energy.

Preliminary knowledge of molecular kinetic theory

Objects are made up of a large number of molecules

Molecules are constantly making irregular movements

There are interaction forces between molecules.

1. Internal energy

1. Molecules have kinetic and potential energy

①The moving basketball has kinetic energy

Conclusion: Moving molecules also have kinetic energy.

The energy possessed by molecules due to their irregular motion is called molecular kinetic energy.

②The stone and the earth attract each other and have potential energy

Do molecules that attract each other also have potential energy?

Conclusion: Molecules that attract each other also have potential energy

The parts of a compressed spring repel each other and have potential energy.

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

Conclusion: Molecules that repel each other also have potential energy.

The energy due to the interaction between molecules is called molecular potential energy

2. internal energy of object

The sum of the kinetic energy of thermal motion and the potential energy of molecules of all the molecules that make up an object is called the internal energy of the object.

The unit of internal energy is Joule (J)

Mechanical energy is related to the mechanical motion of the entire object, and internal energy is related to the thermal motion of the molecules inside the object and the interaction between molecules, so internal energy is another form of energy different from mechanical energy.

2. Changes in the internal energy of an object

(1) Heat transfer:

1. Direction: from high temperature to low temperature

2. Condition: temperature difference

3. Termination: The temperature is consistent

4.Essence: transfer of internal energy

2. How to change the internal energy of an object

(1) Heat transfer can change internal energy

When heat transfer occurs, the energy in a high-temperature object decreases and the energy in a low-temperature object increases.

In the process of heat transfer, the amount of energy transferred is called heat, and the unit of heat is joules.

The internal energy of an object increases when it absorbs heat and decreases when it releases heat.

The more heat it absorbs or releases, the greater its internal energy changes.

The essence of heat transfer: the transfer of internal energy from one object to another.

small experiment

As shown in Figure 1, a small ball of cotton dipped in ether is placed in a thick glass tube equipped with a piston. What will happen when the piston is pressed down quickly? Why?

Cotton can catch fire.

Because the piston does work to compress the air, the internal energy of the air increases and the temperature rises, reaching the ignition point of ether, causing the cotton to burn.

There is some water in a large-mouth glass bottle, and there is water vapor above the water. Inflate the bottle. When the cork jumps up, observe what changes happen inside the bottle? Why?

When the cork jumps up, white mist appears inside the bottle.

When the cork jumps up, the air pushes the cork to do work on the cork. The internal energy decreases, the temperature decreases, and the water vapor in the air liquefies when it is cold.

Case Analysis

A. Do work on an object

B. The object does external work and its internal energy decreases.

Thinking: What is the essence of work changing internal energy?

Conversion between internal energy and mechanical energy

(2) Doing work can change internal energy

The nature of work changing internal energy: the mutual conversion of mechanical energy and internal energy.

Class summary

1. Internal energy

The sum of the _______ caused by the random movement of all molecules inside an object and the _______ caused by molecular interactions is called the internal energy of the object.

2. Changes in internal energy

1.Method

A. Heat transfer. B. Work

2. A measure of how much internal energy changes

A. Heat Transfer Measured by the amount of heat transferred

B. Work is measured by the amount of work done.

3. Heat transfer and work change are equivalent to changing the internal energy of an object.

practice

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 an object increases, _______________ must increase, so the internal energy of this object _________.

3. In winter, breathing into your hands with your mouth will warm your hands. This is to increase the internal energy of the hands in a _______ method, and its essence is that the internal energy is _______ between objects. Rubbing your hands can also warm your hands. , this is to increase the internal energy of the hand using _______ method. In this process, ______________ energy is converted into internal energy.

4. During the experiment of "pumping air into a bottle containing a small amount of water", the teacher kept pumping air into the bottle, so that the pressure of the water vapor in the bottle increased, and the internal energy of the water vapor _______ (fill in "increase" or "decrease"), temperature_______ (fill in "increase" or "decrease").

When the cork jumps up, you can see ________ inside the bottle. This is because water vapor _________ on the cork, and the internal energy ________ (fill in "increase" or "less"). Temperature_______ (fill in “increase” or “decrease”). Water vapor ________ to form small droplets. When the white mist does not disappear, if you immediately close the stopper and pump air into the bottle again, you will see ________.

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For more information about the PPT courseware "Internal Energy of Objects, Internal Energy and Heat Engines", please click the "Internal Energy of Objects ppt Internal Energy and Heat Engines ppt" tab.

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Update Time: 2024-11-24

This template belongs to Physics courseware Shanghai Science Edition Ninth Grade Physics industry PPT template

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