"Pressure" PPT courseware 8

Description

"Pressure" PPT courseware 8

learning target

(1) Understand the concept of stress and what factors are related to the effects of stress;

(2) Master the concept, calculation formulas, and international units of pressure, and be able to use formulas to perform simple calculations;

(3) Understand the methods of increasing and decreasing pressure;

1. Pressure

1. The force that presses vertically on the surface of an object is called pressure

The force of a child pressing vertically on the ground

The force of the thumbtack pressing vertically against the wall

The force exerted by the block vertically pressing on the incline

2. The relationship between pressure and gravity

1) Pressure is not gravity. Pressure can be caused by gravity or other forces

2) Pressure is not necessarily equal to gravity

3) The pressure is equal to the gravity only when the object is placed freely and horizontally

2. Factors affecting the effect of pressure

Do it as shown in the picture and give it a try

How do the two fingers feel different?

Observe the difference between the indentations of the two fingers?

Want to discuss

Two people exert similar pressure on the snow, but does the pressure have the same effect?

What factors do you think are related to the effect of stress?

3. Pressure

1. Definition: The ratio of the pressure on an object to the force-bearing area.

Let p represent the pressure, F represent the pressure, and S represent the stressed area.

Formula p=F/s

Pressure is numerically equal to the pressure per unit area of ​​an object. The greater the pressure, the more obvious the effect of pressure.

2. Units of pressure:

International unit: Pascal Abbreviation: Pa Symbol: Pa

Fold a piece of newspaper in half and lay it flat on the ground. The pressure on the ground is about 1 Pa.

1 Pa means that the pressure exerted by an object on an area of ​​1 m2 is 1 N.

4. Methods of increasing and decreasing pressure

Want to discuss

The tractor is working in the muddy field. In order not to sink into the soil, what methods do we use to reduce the pressure on the ground?

1. Reducing the pressure can reduce the pressure or increase the stress area.

Give it a try:

Why do we feel that sitting on a soft sofa is more comfortable than sitting on a hard bench?

That is because the sofa has a large contact area with the human body after being deformed by force; the bench does not deform very much and has a small contact area with the human body. According to the knowledge of pressure, the sofa exerts less pressure on the human body, so people feel comfortable.

2. Increasing the pressure can increase the pressure or reduce the stress area.

Summary of this lesson

What did you gain from studying this class?

1. Pressure: the force pressing vertically on the surface of an object

2. Pressure: (in physics, pressure is used to express the effect of pressure)

1. Definition of pressure: The pressure exerted on an object per unit area is called pressure.

2. Pressure formula: p=F/s

3. Methods of increasing and decreasing pressure

1. Methods to increase pressure:

(1) When the stress area remains unchanged, increase the pressure;

(2) When the pressure remains unchanged, reduce the stress area.

2. Methods to reduce pressure:

(1) When the stress area remains unchanged, reduce the pressure;

(2) When the pressure remains unchanged, increasing the stress area reduces the pressure.

Practice in class

1. As shown in the figure, the volumes and densities of three solid objects A, B, and C are the same. Their pressures on the horizontal desktop are FA, FB, and FC respectively. Their pressures on the desktop are pA, pB, and pC respectively. Then the relationship between the three pressures is __________, and the order of pressure from small to large is __________.

2. The pressure and pressure a person exerts on the ground when walking is compared to when the person is standing on the ground ( ).

A. Pressure remains unchanged, pressure changes B. The pressure remains unchanged, the pressure remains unchanged

C. Pressure changes, pressure changes D. Pressure changes, pressure remains the same

3. Xiaoli bought a watermelon. She carried it home in a plastic bag. Not long after walking, she felt her hand being strangled by the plastic bag. Based on the physics knowledge we have learned, please help her find a solution to the problem. , and explain the rationale for doing so.

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Update Time: 2024-11-05

This template belongs to Physics courseware Lu Jiao Edition Eighth Grade Physics Volume 2 industry PPT template

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