"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 3

Description

"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 3

1. Gravity

The force on an object due to the attraction of the earth

The object exerting force by gravity is: Earth

Water always flows from high to low

Apples always fall to the ground

2. Description of gravity

1. In daily life, the amount of gravity exerted by an object is often referred to as its weight.

2. Gravity is represented by G.

3. The unit of gravity is: Newton (N).

4. The gravity of an object is measured with a spring dynamometer.

3.Quality

1. The amount of matter an object contains is called mass.

2. Mass is represented by m (or M).

3.Unit of mass

SI unit of mass: kilogram (kg)

There are also grams (g) and tons (t)

1t=1000kg; 1kg=1000g.

4. The size of gravity

1. Size: G = mg

G — Gravity (N); g = 9.8 N/kg

2. The physical meaning of g:

It means that the gravity exerted by an object with a mass of 1 kilogram is 9.8 Newtons. The unit of g: N/kg

3. Take 10 N/kg for rough calculation.

Example: The mass of a small ball is 100g, what is the gravity N it experiences?

It is known that: m=100g=0.1kg, g=9.8N/kg.

Asking for: G＝?

Solution: According to G=mg, we get

G＝mg＝0.1kg×9.8N/kg＝0.98N

Answer: The gravity it experiences is 0.98N.

5. Direction of gravity

What is the direction of gravity on an object?

Use a thread to hang an object. When the object is stationary, the direction of the thread is called the vertical direction. The vertical direction is always perpendicular to the horizontal direction and points toward the center of the earth.

The direction of gravity is vertically downward.

6. The point of action of gravity

1. The point where gravity acts on an object is called the center of gravity

2. The center of gravity of an object with uniform mass distribution and regular shape

on its geometric center. For example: the center of gravity of a spherical object is at the center of the sphere.

7. Information window

1. Stability: The degree of stability of an object

2. Methods to improve stability:

a. Increase the support area

b. Lower the center of gravity

summary:

1. Gravity size: G = mg

2. The physical meaning of g

3. The direction of gravity is vertically downward.

4. The center of gravity of an object with uniform mass distribution and regular shape is at its geometric center.

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Update Time: 2024-11-19

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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