"Rational Utilization of Mechanical Energy" Machinery and Human PPT Courseware

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"Rational Utilization of Mechanical Energy" Machinery and Human PPT Courseware

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What is "doing work"?

When a force acting on an object causes the object to pass a certain distance in the direction of the force, it is said that the force has done work on the object.

Observe and think

Observation and comparison: Think about the fact that the small ball, the heavy hammer, and the bow and arrow can all do work to the outside world, but are the reasons for doing work (having energy) the same?

The small ball in Figure 1 has energy due to the work done by ________ on the wooden block.

The heavy hammer in Figure 2 has energy due to the work done by ________ on the wooden pile.

The bow in Figure 3 has energy due to the work done by ________ on the arrow.

The moving ball has the ability to do work

A lifted weight has the ability to do work

The deformed bow string has the ability to do work

In physics, the ability of an object to do work is called energy.

How much work an object can do is how much energy it has.

Experimental conclusion: If an object can do work on other objects, we say that the object has energy.

Consider whether the following objects have energy

Moving water, open bow, moving air - wind, moving train, people,

Note: As long as an object can do work on other objects, then this object has energy; if an object cannot do work on other objects, then this object does not have energy.

Unit of energy - Joule

Since energy and work are closely related, the process of doing work is the process of energy conversion. The more work an object does, the more one type of energy is converted into another type of energy. Therefore, the unit of energy is the same as the unit of work, which is also the joule. .

Moreover, energy cannot be generated or destroyed out of thin air. It is only converted from one form of energy into another form of energy.

Design experimental plan:

Information: Small balls with different masses are released from the same height of an inclined plane and have the same speed when moving to the horizontal plane.

1. Select the instrument:

2. Experimental ideas:

The more work an object can do, the more energy it has

To compare the magnitude of kinetic energy, compare the distance the block moves

3. Experimental methods:

Since the magnitude of kinetic energy may be related to multiple factors, the control variable method should be used during the experiment.

First control the speed to be the same and study the relationship between kinetic energy and mass.

Then control the mass to be the same and study the relationship between kinetic energy and speed.

4. Steps and records:

potential energy

Potential energy: The energy an object possesses when it is lifted up or elastically deformed.

When a shot put on a sponge, the soft sponge will be deformed by pressure, which shows that the shot has energy. The energy that an object like a shot put has because it is lifted up is called gravitational potential energy.

An expanded bow can shoot arrows from the bow, which means that the expanded bow has energy. The energy that an expanded bow has due to the deformation of an object is called elastic potential energy.

think about it

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

Height generally refers to the height above the ground unless otherwise specified.

What factors may determine the magnitude of gravitational potential energy?

guess:

1. The magnitude of gravitational potential energy is related to the height at which the object is lifted.

2. The magnitude of gravitational potential energy is related to the mass of the object

1. What is elastic potential energy?

The energy an object possesses due to elastic deformation

After the external force is removed, the deformation can be completely restored to the original shape.

2. What factors are related to the size of elastic potential energy?

The magnitude of elastic potential energy may be related to elastic deformation. For example: draw a bow and shoot an arrow

in conclusion:

The size of the elastic potential energy is related to the size of the deformation. The greater the deformation of the object, the greater the elastic potential energy.

3. Mutual conversion of kinetic energy and potential energy

1. A table tennis ball thrown vertically, the speed and height changes of the ball as it rises and falls.

During the rising process of the table tennis ball, it moves slower and slower, the gravitational potential energy increases and the kinetic energy decreases; during the falling process, the table tennis ball moves faster and faster, the gravitational potential energy decreases and the kinetic energy increases.

Therefore, the kinetic energy of the table tennis ball is converted into potential energy during the rising process; the potential energy is converted into kinetic energy during the falling process.

2. Move the pendulum up and down, observe the speed and height changes of the roll, and analyze the conversion of kinetic energy and potential energy.

When the roll falls, it rolls faster, the gravitational potential energy decreases, and the kinetic energy increases; when the roll rises, it rolls slower, the gravitational potential energy increases, and the kinetic energy decreases.

Therefore, when the roll falls, gravitational potential energy is converted into kinetic energy; when the roll rises, kinetic energy is converted into gravitational potential energy.

Practice in class

1. Fill in the blanks

1. The sum of kinetic energy and potential energy is called ________. Kinetic energy is the energy that an object has when it ________, and potential energy is the energy that an object has when it ______________.

2. The factors that affect kinetic energy are ________ and _________.

3. Factors that affect gravitational potential energy include __________ and ___________.

4. The same object ____________, the greater its elastic potential energy.

2. Judgment

1. As long as it is a spring, it has elastic potential energy. ( )

2. A bird flying at high altitude only has kinetic energy. ( )

3. Objects with high speed must have high kinetic energy. ( )

4. An object hung from the ceiling by a thin wire does no work, but it also has energy ( )

5. A moving object must have kinetic energy. ( )

6. Things on the second floor must have less gravitational potential energy than things on the third floor. ( )

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"Rational Utilization of Mechanical Energy" Machinery and Human PPT Courseware 2:

"Rational Utilization of Mechanical Energy" Machinery and Human PPT Courseware 2 1. Understanding Energy 1. If an object can do work, we say it has energy. 2. The more work an object can do, the more energy it has. 3. Unit of energy: joule (J) The following objects have energy...

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Update Time: 2024-11-18

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