"Simple Machinery" PPT courseware

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"Simple Machinery" PPT courseware

Part One: The Concept of Leverage

A hard rod that can rotate around a fixed point under the action of force is called a lever.

The lever can be straight or curved.

But it must be hard, not soft.

Five Elements of Leverage

Fulcrum, power, resistance, power arm, resistance arm

Special attention should be paid to the fact that the moment arm is not the distance from the fulcrum to the point of action of the force, but the vertical distance from the fulcrum to the line of action of the force. Don't be careless when doing the questions, keep them in mind.

Simple Machinery PPT, Part 2 Content: Thinking and Discussion:

1. Does the moment arm have to be on the lever?

Answer: No

2 Are the levers all straight?

Answer: The lever can be straight or curved

3. If a force acts on a lever and the point of action remains unchanged but the direction of action changes, does the moment arm change?

Answer: To change

How to draw the lever arm:

(1) Identify leverage;

(2) First find the fulcrum O;

(3) Draw power and resistance;

(4) Draw the line of action of the force;

(5) The vertical segment L of the line of action of the force passing through the fulcrum 0 is the moment arm.

Simple Machinery PPT, Part 3: Classroom Exploration

Explore Under what conditions does leverage balance?

There are two adjustable nuts at both ends of the lever. What do they do?

Why is the lever required to be in a horizontal position when it is at rest?

Function: Adjust the lever to balance in the horizontal position before the experiment

Because in this way the value of the force arm can be read or measured directly on the lever.

Simple Machinery PPT, Part 4: Fixed Pulley and Moving Pulley

fixed pulley

Characteristics of fixed pulley

The essence of the fixed pulley is an equal-arm lever

A: The fulcrum is at the axis O.

B: Power arm l1 is equal to resistance arm l2

It doesn’t save effort or distance, but it can change the direction of the force.

moving pulley

Moving pulley: A pulley that moves with the hook code.

1. The essence of the moving pulley: an unequal arm lever that saves half the force

2. The characteristics of the moving pulley are as follows:

① When using the movable pulley, the direction of force cannot be changed. The direction of force used to lift a heavy object using a movable pulley is the same as that of lifting a heavy object directly by hand.

②The function of the movable pulley is to save half the force (F=G/2), but according to the characteristics of the labor-saving lever, it saves effort and distance, when using the movable pulley to lift heavy objects, it takes twice the distance. That is, to make the weight rise (or fall) to a height h, the free end of the rope needs to rise (or fall) a distance of 2h.

③When using a movable pulley to lift heavy objects, if the dead weight of the movable pulley cannot be ignored, the free end tension F = (G + G motion)/2

(Excluding rope weight and mechanical friction)

Pulley block:

1. Connect the fixed pulley and the movable pulley together to form a pulley system, also called a pulley block.

2. The role of the pulley set: Using the pulley set can save effort (the amount of effort saved depends on how many sections of rope share the resistance); in some cases, the use of the pulley set can also change the direction of the force.

Simple Machinery PPT, Part 5: Mechanical Efficiency:

1. Useful work, useless work (extra work) and total work: total work = useful work + extra work

2. Mechanical efficiency: the ratio of useful work to total work, which reflects the proportion of useful work in the total work.

The greater the mechanical efficiency, the higher the energy utilization rate when the machine is working.

η=W useful/W total

The mechanical efficiency of general pulley blocks is 50%~70%, that of cranes is 40%~50%, and that of water pumps is 60%~80%. When using machinery, always minimize additional work to improve mechanical efficiency.

3. The relationship between mechanical efficiency and power

There is no necessary connection between mechanical efficiency and power. Power is a physical quantity that expresses the speed of work, while mechanical efficiency indicates the utilization rate of the total work of the machine. A machine with high power may not necessarily be efficient. For example, a diesel locomotive has a power of tens of thousands of watts, but its efficiency is only 30% to 40%, while an electric toy car has a power of only a few watts, but its efficiency can reach 80%.

4. How to improve mechanical efficiency: Mechanical efficiency depends on two factors: useful work and total work. To improve mechanical efficiency, generally consider the following aspects:

①When the total work is constant, the more useful work (that is, the less extra work), the higher the mechanical efficiency. ②When the useful work is constant, the less the total work (that is, the less the extra work), the higher the mechanical efficiency. ③When the additional work is constant, the more the total work (that is, the more useful work), the higher the mechanical efficiency.

Keywords: Zhejiang Education Edition ninth grade science PPT courseware free download, simple machinery PPT download, .PPT format;

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Update Time: 2024-11-03

This template belongs to science courseware Zhejiang Education Edition Ninth Grade Science Volume 1 industry PPT template

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