"Lever" Simple Machine Function PPT Courseware 2

Description

"Lever" Simple Machine Function PPT Courseware 2

Review of old knowledge

The concept of leverage

A hard rod that can rotate about a fixed point under the action of force.

Elements of Leverage

Fulcrum, power, power arm, resistance, resistance arm

Schematic diagram of lever

(1) Find the fulcrum

(2) Draw the extension line of the force

(3) Mark the shortest distance from the extension line to the fulcrum

learning target

(1) Master the balancing conditions of leverage;

(2) Understand the classification and application of leverage.

1. Conditions for leverage balance

Think about it: How do you keep a seesaw level?

What are your thoughts?

1) Let two students with the same weight sit at the same distance from the axis of rotation.

2) Let students who don’t use their weight adjust the distance to the rotating axis according to the status of the seesaw.

When the lever is stationary or rotates at a constant speed under the action of power and resistance, we call it lever balance.

Observation and Experimentation

Ask a question

What conditions must be met for leverage balance?

Conjectures and Assumptions

When the lever is balanced, what is the relationship between power and power arm and resistance and resistance arm?

Design experiments and develop plans

Step 1: Adjust the nuts at both ends of the lever so that the lever is in a horizontal balance state.

Step 2: Hang different numbers of hook codes on both sides of the lever.

Step 3: Move the position of the hook code so that the lever is in a balanced state.

Step 4: Organize each experimental data and fill in the table below.

Analysis and Demonstration

Analyze the data in the table in conjunction with the demonstration to find out the relationships between them. What conclusions can you draw about the equilibrium conditions for leverage?

Evaluate

Leverage balance conditions:

Power × power arm = resistance × resistance arm, that is

F1 x L1=F2 x L2

2. Application of leverage

Thoughts and Summary

We can divide leverage into three categories

(1) Labor-saving lever: The power arm is larger than the resistance arm, so this kind of lever is labor-saving to use;

(2) Equal-arm lever: The power arm is equal to the resistance arm. This kind of lever is neither labor-saving nor labor-intensive to use;

(3) Effortless lever: The power arm is smaller than the resistance arm, so this type of lever is laborious to use.

Summary of this lesson

What did you gain from studying this class?

Leverage balance condition

Content: Power times power arm equals resistance times resistance arm

Expression: F1×L1=F2×L2

Classification and application of leverage

Labor-saving lever: the power arm is larger than the resistance arm, saving effort

Equal-arm lever: power arm equals resistance arm

Effortless lever: the power arm is smaller than the resistance arm, effortful

Practice in class

1. Two children sit on the seesaw and are balanced horizontally. At this time ( )

A. The gravity of the two children must be equal

B. The distance between the two children and the fulcrum must be equal

C. The moment arms of the two children must be equal.

D. The child's gravity is equal to the product of their respective distances from the fulcrum.

2. Among the following statements about leverage, which one is correct ( )

A. The fulcrum is always located between the power action point and the resistance action point

B． The longer the power arm, the less effort is always required

C． The greater the ratio of the power arm to the resistance arm, the less effort is required

D. The direction of action of power is always opposite to the direction of action of resistance

3. During the holidays, Xiaolan participated in a family game activity with her father and mother. The activity requirements are: any two members of the family stand on the wooden board as shown in the picture, so that the wooden board is balanced horizontally. If Xiaolan and her father weigh 400 N and 800 N respectively, and Xiaolan stands on one side 2 m away from the central fulcrum, how far away from the fulcrum should her father stand to balance the board horizontally?

Solution: The forces exerted by Xiaolan and her father on the lever are F1=400 N and F2=800 N respectively. The moment arm of F1 is l1=2 m. Adjust F1L1=F2L2 according to the balance of the lever, so l2=F1l1/F2=1 m. That is, dad should stand on the other side 1 m away from the fulcrum.

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For more information about the "Lever Simple Mechanical Work" PPT courseware, please click the Lever PPT Simple Mechanical Work PPT tab.

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Update Time: 2024-09-12

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