"Simple Machines" PPT (Lesson 3)

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"Simple Machines" PPT (Lesson 3)

Part One: Learning Objectives

1. Understand fixed pulleys and movable pulleys.

2. Be able to describe the characteristics of the fixed pulley and the movable pulley, and explain that the fixed pulley is essentially a lever

3. Understand the characteristics of pulley blocks

Simple Machinery PPT, Part 2: Pulley

A wheel with grooves on the periphery that can rotate around a central axis.

Question: How many ways can you use a pulley, a thin wire, or an iron platform to lift an object? And through experiments, study the characteristics of the pulley you use?

An exploration of pulleys

Exploration 1: What are the advantages of fixed pulleys?

1. Use a spring scale to measure the weight G1 of the hook code.

2. Use the spring scale to pull the hook code at a constant speed through the fixed pulley. The spring scale reads F1 and compares it with G1.

3. Change the direction of the pulling force, as shown in Figure C. Pay attention to whether the reading F of the spring scale changes. At the same time, pay attention to the relationship between the pulling distance of F1 and the rising height of the weight.

Fixed pulleys cannot save labor; why are they still used?

Conclusion: Using fixed pulleys cannot save effort; but it can change the direction of force.

Exploration 2: What are the advantages of moving pulleys?

1. Use a spring scale to measure the total weight G2 of the hook code and pulley, pull the hook code through the movable pulley with a spring scale at a constant speed, and compare the reading F2 of the spring scale with G2. At the same time, pay attention to the relationship between the F2 pull distance and the lifting height of the weight.

Conclusion: The moving pulley saves half the effort, but requires more movement.

Simple Machinery PPT, Part 3: Fixed Pulley and Moving Pulley

1. Fixed pulley: a pulley with a fixed shaft.

Features: It cannot save effort, but it can change the direction of force.

2. Moving pulley: a pulley in which the rotating shaft moves together with the weight.

Features: It can save half the effort, but cannot change the direction of the force.

The moving distance of the pulling force is 2 times the distance the object rises s = 2h

Why can't the fixed pulley save effort, but the movable pulley can save half the effort?

Simple Machinery PPT, Part 4: Pulley Block

It consists of a fixed pulley and a movable pulley.

Conclusion: The magnitude of the pulling force F is related to the number n of the rope strands used to lift the movable pulley.

Study 3: Labor saving of pulley block

The method to determine n: make a crosscut between the fixed pulley and the movable pulley, and the number of ropes hanging the movable pulley is n

When using a pulley block, the movable pulley is hoisted by several strands of rope, and the force used is a fraction of the weight of the object and the movable pulley, that is, F = 1/n (G object + G motion)

The distance the pull moves is several times the distance the weight moves. (Although using a pulley block saves effort, it costs distance) S=nh

Simple Machinery PPT, Part 5: Consolidation Exercises:

1: As shown in the figure (a) below, object B weighs 100N. When it rises at a constant speed under the action of force F, F should be equal to ____N. (excluding friction)

2: As shown in the figure (b) above, the weight of object A is 100N, and the pulling force of the hook hanging the heavy object is __N. The force of a person pulling the rope at a constant speed is __N (the dead weight of the movable pulley is not included)

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Update Time: 2024-10-02

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

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