"Scientific Inquiry: Balance Conditions of Lever" Machinery and Human PPT Courseware 4

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"Scientific Inquiry: Balance Conditions of Lever" Machinery and Human PPT Courseware 4

Activity 1 Observation experience

Do this: ① Clamp things with tweezers ② Cut paper with scissors ③ Use a ruler to pry the stationery box

Take a look at: the tools in the picture, think about and discuss the common characteristics of how they work

Activity 2 Explore the balance of levers

1. Ask questions

What are the factors that influence the seesaw to remain stationary in a horizontal position?

Influencing factors

1. The force exerted on the lever

2. Distance

2. Make plans and design experiments

3. Conduct experiments and collect evidence

4. Analysis and demonstration

Thinking: The conditions for balanced leverage levels are:

(1) What are the factors that affect the balance of leverage levels?

(2) When observing experimental data and analyzing leverage balance, what is the relationship between these factors?

How to draw a lever arm

Find the point (find the fulcrum)

2. Draw the line (draw the line of action of the force)

Draw three vertical line segments (draw a vertical line segment from the fulcrum to the line of action of the force)

Mark the four symbols next to them (mark the vertical foot - the right angle symbol, mark the force arm - the distance from the fulcrum to the vertical foot, use ι1 to represent the power arm, and ι2 to represent the resistance arm.)

training ground

1. Regarding the drawing of F moment arm in the figure, the correct one is ( )

2. As shown in the figure, the lever is just balanced after being hung with hooks. The mass of each hook is the same. In the following situations, the lever can still maintain balance ( )

A. The left and right hook codes move one space each toward the fulcrum.

B. Reduce one hook code on each side

C. Reduce the hook code by half on each side

D. Add two hook codes on the left and right sides

3. Happy competition

"A small weight can weigh a thousand pounds", let's compare who can say it faster and who can say it better!

Review the past and learn the new

Find the point (find the fulcrum)

2. Draw the line (draw the line of action of the force)

Draw three vertical line segments (draw a vertical line from the fulcrum to the line of action of the force)

Write the four-hand symbol next to it (the force arm symbol)

Please take the water well handle as an example to find out the five elements of leverage

Classification of leverage

Activity 1: Please combine the lever balance conditions to analyze the relationship between power F1 and resistance F2 when l1>l2, l1

Leverage balance condition: F1l1=F2l2 when the leverage is balanced

Three types of leverage:

If l1>l2, then F1

If l1F2

If l1=l2, then F1=F2

Summary: To determine the type of lever, you actually need to compare the size of the power arm and the resistance arm.

Various scissors

Thinking: Are scissors all labor-saving levers? Under what circumstances do people use hard leverage? What are the benefits of using effortful leverage? Are there any disadvantages to labor-saving levers?

When the resistance is small, people will use the effort lever.

Using a laborious lever saves distance and is very convenient.

The disadvantage of labor-saving levers is the distance required.

Class exercises

1. Two forces act on both ends of the lever to balance the lever, then ( )

A. The magnitude of these two forces must be equal

B. The moment arm lengths of these two forces must be equal

C. The one with the longer moment arm has greater force.

D. The one with the longer moment arm has smaller force

2. To balance the lever AOB, draw the direction of the minimum force F acting at point A in the figure:

1. Find the point (find the point A farthest from the fulcrum O)

2. Draw a line (draw a line connecting OA)

Make three vertical line segments (make OA vertical line from point A in a reasonable direction)

Write the four symbol next to it (Force F symbol)

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For more information about the PPT courseware "Machine and Human Science Exploring the Balance Conditions of Levers", please click the "Machines and Humans ppt Science Exploring the Balance Conditions of Levers ppt" tag.

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Update Time: 2024-11-13

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

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