"Gravity" Motion and Force PPT Courseware

Description

"Gravity" Motion and Force PPT Courseware

Thinking: Why don’t apples, water, people, etc. fall to the sky? Is the earth's gravity attracting it?

1. Gravity

Observe and think

Observing the above scene, what characteristics do the movements of the diver and the thrown basketball have in common?

Concept: The force exerted by an object due to the attraction of the earth is called gravity.

All objects near the Earth are affected by gravity.

Notice

1. The object exerting force by gravity is the earth

2. The objects affected by gravity are all objects on the earth.

2. Direction of gravity

Direction: vertically downward

Application: Heavy vertical line

When laying bricks, construction workers often use thin wires hanging heavy objects to determine the vertical direction to check whether the wall they are building is vertical.

Want to discuss

We stand on the ground, feet down, standing very firmly. But the earth is spherical, and the Argentinians "under our feet" seem to have their feet pointing upward. Why do they also stand firm? What is the direction that we usually refer to as "down"?

3. The relationship between gravity and mass

Experimental exploration: What factors are related to the magnitude of gravity?

Guess the magnitude of gravity is related to ______________?

design experiment

Use a spring dynamometer to measure the mass of different hook codes, as shown in the picture on the right.

The relationship between gravity and mass

1. The gravity exerted on an object is proportional to its mass

2. The ratio of gravity to mass is approximately 9.8N/kg

3. If g is used to represent this ratio, the relationship between gravity and mass can be written as G/m=g or G=mg

The physical meaning of g =9.8N/kg

An object with a mass of 1kg experiences a gravitational force of 9.8N

4. Center of gravity

Concept: Equivalent point of action of gravity

The center of gravity of an object with uniform texture and regular shape is at its geometric center

The center of gravity of a disc with uniform mass and regular shape is at the center of its circle

How to determine the center of gravity of an object with uneven and irregular masses?

Find the center of gravity using the hanging method

Class summary

1. Gravity: the force exerted on an object due to the attraction of the earth, symbol G

2. Direction of gravity: vertically downward

3. The relationship between gravity and mass:

The gravitational force on an object is proportional to the mass of the object.

G=mg G—Gravity—Newton (N)

m—mass—kilogram (kg)

4. The point of action of gravity: center of gravity

self-test

1. When a high jumper jumps into the air, if the air resistance is not considered, the athlete will be affected by ______, and this force is exerted by ______.

2. The force exerted on objects due to the attraction of the earth is called _____; all objects on the earth are affected by _____.

3. The secret of the toy "tumbler" standing up automatically after being knocked down is ( )

A. The gravity is too small and can be ignored. B. The center of gravity is low and it is not easy to tip over.

C. The direction of gravity is always vertically downward. D. There is an automatic lifting device inside.

4. Which of the following statements about gravity is correct ( )

A. The direction of gravity is vertically downward

B. Only objects in contact with the ground are affected by gravity.

C. The direction of gravity is vertically downward

D. The apple falls due to the greater gravity on the apple.

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Update Time: 2024-09-17

This template belongs to Physics courseware Beijing Normal University eighth grade physics volume 2 industry PPT template

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