"Mechanical Energy and Its Transformation" Work and Mechanical Energy PPT Courseware 3

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"Mechanical Energy and Its Transformation" Work and Mechanical Energy PPT Courseware 3

Warm up before class

1. The ability of an object to do work is called energy, and kinetic energy and potential energy are collectively called _______.

2. Explain what form of mechanical energy the following objects have.

①Middle school students who climb mountains_______

②The water in the barrage ________

③The bird flying in the sky______

④The rotating wheel______

⑤The small tree bent by the wind_______

3. After a skydiver jumps from an airplane in the sky, during the fall before the parachute opens, the athlete’s ( )

A. Kinetic energy increases and gravitational potential energy decreases

B. Kinetic energy decreases and gravitational potential energy increases

C. Kinetic energy decreases and gravitational potential energy decreases

D. Kinetic energy increases and gravitational potential energy increases

4. When an object is acted upon by a pair of balancing forces, its ( )

A. Kinetic energy remains unchanged

B. Kinetic energy may increase or decrease

C. Gravitational potential energy must decrease

D. Gravitational potential energy must increase

Kinetic energy and potential energy can be converted into each other

Definition of mechanical energy: sum of kinetic energy and potential energy

1. During the downward movement of the pendulum, the gravitational potential energy decreases, the kinetic energy increases, and the gravitational potential energy is converted into kinetic energy.

2. During the upward movement of the roll, the kinetic energy decreases, the gravitational potential energy increases, and the kinetic energy is converted into gravitational potential energy.

Think about it, do it

think:

1. Will the iron lock touch your nose when it swings back? Is there any other energy transformation involved?

2. What would happen if there was no resistance?

Analyze the conversion of kinetic energy and potential energy

1. When a satellite moves from apogee to perigee, how do its potential energy, kinetic energy, and speed change? When a satellite moves from perigee to apogee, how do its potential energy, kinetic energy, and speed change?

2. At perigee, the satellite has the most kinetic energy and potential energy. At apogee, the satellite has the most kinetic energy and potential energy.

Conversion of kinetic energy and elastic potential energy

When the bow is stretched and the arrow is shot out, the elastic potential energy of the bow decreases, the kinetic energy of the arrow increases, and the elastic potential energy of the bow is converted into the kinetic energy of the arrow.

What other examples can you give in life?

When the iron ball compresses the spring, the kinetic energy of the iron ball decreases, the elastic potential energy of the spring increases, and the kinetic energy is converted into elastic potential energy.

During the recovery process of the spring, the elastic potential energy of the spring decreases, the kinetic energy of the iron ball increases, and the elastic potential energy is converted into kinetic energy.

conservation of mechanical energy

Kinetic energy and potential energy are collectively called mechanical energy.

If there is no frictional resistance, only kinetic energy and potential energy are converted into each other, and the total amount of mechanical energy remains unchanged.

Class exercises

1. The spring door can close by itself after being pushed open. This process will be explained from the perspective of energy conversion.

When the spring door is pushed open, the kinetic energy is converted into elastic potential energy; when the spring door is automatically closed, the elastic potential energy is converted into kinetic energy.

2. Explain the conversion of mechanical energy in the following processes:

(1) The sled slides down the hillside

Gravitational potential energy is converted into kinetic energy

(2) The cannonball is shot diagonally upward from the muzzle and then falls back to the ground in the distance.

Kinetic energy is converted into gravitational potential energy and then into kinetic energy

3. Analyze the energy transformation during the process of the ball falling and bouncing from the hand.

When the ball falls to the ground, _______ energy is converted into _____ energy; when it hits the floor, ____ energy is converted into _______ energy; when it recovers its deformation (without leaving the ground) and bounces upward, _______ is converted into _____ energy , when bouncing upward from the ground, _____ energy is converted into _______ energy.

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Update Time: 2024-09-27

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 2 industry PPT template

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