"Internal Energy and Its Changes" Heat and Energy PPT Courseware 4

"Internal Energy and Its Changes" Heat and Energy PPT Courseware 4

1. Internal energy

Since ancient times, people have been searching for some kind of energy related to heat.

Is "heat" a kind of energy? Does it work?

1. Molecules have kinetic and potential energy

The molecules that make up matter are constantly undergoing thermal motion and also have kinetic energy, and the interaction between molecules gives them 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.

Because the molecules of all objects are constantly moving irregularly, all objects have internal energy.

2. Changes in the internal energy of an object

1. The internal energy of an object decreases when its temperature decreases, and increases when its temperature increases.

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.

(2) Doing work can change internal energy

in conclusion:

When work is done on an object, the internal energy increases and the temperature rises.

When an object performs work on the outside, its internal energy decreases and its temperature decreases.

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

practice

1. During the experiment of "pumping air into a bottle containing a small amount of water", the teacher continued to pump 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 _________.

2. Among the following options, the change in the internal energy of an object is achieved through work ( )

A． On a hot summer day, put some ice cubes in your beer and it will become cooler

B． The water in the solar water heater tank is heated by the sun

C. When a car is running, the tires get hot

D. Strike a match, burn a match

3. NASA scientists believe that the "fireball" phenomenon that appeared on the East Coast of the United States is due to an asteroid entering the Earth's atmosphere. Ask students to try to explain this rare phenomenon.

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