"Gong" Mechanical and Gong PPT courseware

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"Gong" Mechanical and Gong PPT courseware

1. What are the effects of force?

2. The object in the picture is pulled by a rope. What is the effect of the pull?

3. What force contributes to the upward movement of the object?

The definition of work in mechanics

When a force acts on an object and the object moves a certain distance in the direction of the force, mechanics says that the force has done work.

The object is acted upon by a lifting force, but the direction of motion is always F⊥s perpendicular to the direction of the force, and the effort is in vain.

The lifting force F of the forklift moves the goods a distance s. We say that the lifting force of the forklift has done work on the goods, or simply that the forklift has done work on the goods.

Did they all do the work?

The object is acted upon by a force, but remains in a stationary state s=0, and the work is in vain.

The object is not affected by force in the direction of movement and moves due to inertia. F=0, no effort or effort.

What counts as work?

Two necessary factors for doing work

1. A force acting on an object F

2. The object moves a distance s in the direction of the force

From the above examples, can you summarize the circumstances under which an object does not perform work?

1. The object is acted upon by a force but remains at rest.

s=0, no effort

2. The object is not affected by force in the direction of movement and moves due to inertia.

F=0, no effort, no result

3. The object is acted upon by a certain force, but the direction of motion is always perpendicular to the direction of the force.

F⊥s, hard work without success

Calculation of work

Work: The product of force and the distance the object moves in the direction of the force

Calculation formula: work = force × distance moved in the direction of force W = Fs

The meaning and unit of the symbol:

W——work——Joule (J)

F——Force——Newton (N)

s——distance——meter (m)

1J = 1N·m

Example 1: A sled with a mass of 50 kg is loaded with 350 kg of goods. A horse pulls it and transports the goods to a cargo yard 3,000 m away at a constant speed. If the friction force experienced by the sled while traveling is 800 N, find the work done by the horse while transporting the goods. (g=10 N/kg)

Solution: The force used to pull the cart is equal in magnitude and opposite in direction to the frictional force.

F=FMo=800 N

The distance traveled by the horse is s=3 000 m

Ｗ＝Ｆs=800 N×3 000 m=2.4×106 J

Answer: The work done by the horse when transporting goods is 2.4×106 J.

Class summary

1. The concept of work

The product of the force and the distance the object moves in the direction of the force

2. Two necessary factors for doing work

1. Powerful effect

2. Move a certain distance in the direction of the force

3. Calculation and units of work

W＝Fs unit: 1 J＝1 N·m

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Update Time: 2024-09-12

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

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