"Did you work?" 》Machine and Human PPT Courseware 2

Description

"Did you work?" 》Machine and Human PPT Courseware 2

Situation introduction

To understand work in physics, let's analyze a few examples.

1. The lifting force F of the forklift moves the goods a certain distance. 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.

2. The force F of the hammer on the nail moves the nail a certain distance. We say that the force of the hammer does work on the nail, or simply that the hammer does work on the nail.

collaborative inquiry

Exploration Point 1: Mechanical Work

In physics, the product of force and the distance an object moves in the direction of the force is called mechanical work, or "work" for short.

What counts as work?

The two necessary factors for doing work are:

necessary factors

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

Explore Point 2: Calculation of Work

1. In physics, it is stipulated that work is equal to the product of force and the distance traveled by the object in the direction of the force.

That is: work = force × distance

2. Calculation formula: W=F·s

3. Unit of work:

F——N

s——m special unit

W——N·m——Joule (Joule)——J symbol

1J=1N·m

Several issues that must be paid attention to when using the formula of work:

1. F and s in the formula must be on the same straight line;

2. The unit of F in the formula must be (N), the unit of s must be (m), then the unit of work is (J);

3. F and s must be simultaneous: that is, s must be the distance that the object moves in the direction of the force with F's participation;

4. F and s must be identical: that is, F and s refer to the force exerted on the same object and the distance moved in the direction of the force.

Class summary

1.What is gong?

In physics, the product of force and the distance an object moves in the direction of the force is called mechanical work, or "work" for short.

2. What counts as work?

1. The object is subject to force

2. The object must pass a certain distance in the direction of the force

3. How to calculate work

1. The formula of work: work = force × distance W = F·s or G·h

2. Unit of work: Joule (Joule) 1 Joule = 1 Newton meter

Symbol (J) 1 J=1 N·m

In-class training

1. Regarding the concept of work, which of the following statements is correct ( )

A. As long as a force acts on an object, the force does work on the object.

B. As long as the object moves a distance, the force does work.

C. A force acts on the object, and the object moves a distance in the direction of the force, then the force has done work on the object.

D. A force acts on the object and the object moves a distance. This force must have done work.

2. As shown in the figure, an object with a weight of 100 N is pulled by a horizontal force F and moves 5m to the left at a constant speed on the horizontal ground. The friction force on the ground on the object is 20 N, then ( )

A. The work done by gravity is 500 J B. The pulling force is 100 N

C. The pulling force is 120 N. D. The work done by the pulling force is 100 J.

3. Object A moves on a smooth horizontal surface, and object B moves on a rough horizontal surface. Now use the same horizontal thrust to make A and B move the same distance in the same direction. The two works are W A and W respectively. B, then

WA______WB. (Optional "<", "=" or ">")

4. The masses of two containers A and B are equal. Use a crane to lift container A by 10 m at a speed of 1 m/s, and lift container B by the same height at a speed of 2 m/s. Then we have W A ______ W B. (Optional "<", "=" or ">")

5. A student uses a force of 120 N to kick a 4 N football to a distance of 25 m. The correct work done when he kicks the ball is ( )

A. Work done 3000J B. Work done 1000J

C. No work was done D. Work was done, but the conditions were insufficient and it could not be calculated

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For more information about the PPT courseware "Have Machines and People Done Work?", please click the "Have Machines and People Done Work ppt" ppt tag.

"Did you work?" 》Machine and Human PPT courseware:

"Did you work?" 》Machine and Human PPT Courseware Mechanical Work In order to evaluate the effectiveness of machinery, people put forward the concept of work. In physics, the product of force and the distance an object moves in the direction of the force is called mechanical work, or work for short. Students carry schoolbags and walk evenly on the level road...

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Update Time: 2024-11-25

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

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