"Gong" Simple Machinery Gong PPT Courseware

Description

"Gong" Simple Machinery Gong PPT Courseware

learning target

(1) Know the concept of mechanical work;

(2) Master the two necessary factors for doing work;

(3) Understand the calculation of work.

Want to discuss

Observe the two situations below and find what their activities have in common.

(1) All forces act on objects;

(2) All moved distance in the direction of force.

1. The concept of work in physics

Thoughts and Summary

Through the above example analysis, what are the necessary conditions for one object to do work on another object?

necessary conditions

F (force acting on an object)

s (distance the object moves in the direction of the force)

Three typical situations where no work is done

(1) There is a force, but the distance traveled in the direction of the force is zero.

(2) There is distance, but there is no force acting in the same direction as the distance.

(3) There is force and distance, but the directions of force and distance are perpendicular to each other.

2. The size of work

1. Work is equal to the product of the force and the distance the object moves in the direction of the force.

2. Calculation formula of work

Work = Force × Distance W = Fs

3. Units and physical meaning of work

Unit: Joule

That is: 1 J=1N·m

Meaning: The work done by a force of 1 N when the object passes through a distance of 1 m in the direction of the force is 1 J.

Summary of this lesson

What did you gain from studying this class?

1. Mechanical work

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

2. What counts as doing work?

Two necessary factors are met:

(1) A force acting on an object

(2) The distance the object moves in the direction of the force

3. How to calculate work

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 (formula: W=Fs)

Practice in class

1. A football player uses a force of 25 N in the horizontal direction to kick a 10 N ball along the horizontal ground. After being kicked out, the ball rolled on the ground for 30 m before stopping. When the ball rolls, the work done by the foot on the ball is ( ).

A. 750JB. 300 J

C. 450 JD． 0

2. A person is holding a thick stack of books and walking from one end of the corridor to the other. He is exhausted and sweating profusely. Has the person done any work on the ball?

3. After the crane lifted 2×104 kg of goods 3 m high from the ground, it moved 5 m in the horizontal direction. How much work did the crane do?

Solution: The pulling force of the crane is equal to the gravity of the cargo. When moving in the horizontal direction, the pulling force does no work. Therefore, the work done by the crane is:

W＝Fs＝Gh＝mgh

＝2×104 kg×10 N/kg×3 m＝6×105 J

4. On flat ground, a box weighing 100 N is pushed forward 10 m with a horizontal thrust of 50 N. How much work does the child pushing the box do? If the box is lifted 1.5 m at a constant speed, how much work does it do?

Solution: W1＝Fs＝50 N×10 m＝500 J

W2＝ F's '＝Gh=100 N×1.5 m＝150 J

Answer: He does 500 J of work by pushing the box and 150 J by lifting the box.

When the box is pushed forward horizontally, does the weight of the box do any work?

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Update Time: 2024-10-29

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

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