"Elastic Force and Spring Dynamometer" Familiar and Unfamiliar Force PPT Courseware

Description

"Elastic Force and Spring Dynamometer" Familiar and Unfamiliar Force PPT Courseware

【Experience】Feel the elasticity

Activity: Prepare plasticine and a small spring (take your used ballpoint pen), fix one end of the spring, pull the spring with different forces, observe the degree of deformation of the spring, and feel the magnitude of the pulling force with your hands.

Activity 1: Knead the plasticine.

Activity 2: Use a small force F1 to pull a small spring as shown in Figure B.

Activity 3: Use slightly larger force F2 to pull the small spring as shown in Figure C.

Activity 4: Use greater force to pull the small spring into a straight line as shown in Figure D.

(1) In the above activities, the object that can return to its original shape after letting go is _______________________________.

(2) In the above activities, the object that cannot return to its original shape after letting go is ____________________________.

(3) In the figure above, the length of the spring when there is no tension is _______. In Figure B, the length of the spring when it is under tension is _______. Comparing Figures B and C, the length of the spring in Figure _______ changes more. big. The spring in picture D is damaged.

Tips: (1) A small spring stretched with a small force (2) Plasticine, a spring stretched in a straight line (3) L　L1　C

Doubtful about preview

1.What is elasticity?

2. What is the manufacturing principle of spring dynamometer?

3. How to use spring dynamometer correctly?

Explore 1 Elasticity

Combined with "experience", think about the following questions:

1. Why can’t plasticine return to its original shape after deformation, but a spring can?

Reference answer: Plasticine is not elastic, but springs are elastic.

2. When the hand pulls the spring, the hand is also pulled by the spring. How does the spring exert the pulling force on the hand?

Reference answer: The spring is elastic. After elastic deformation, it restores its deformation and exerts a pulling force on the hand.

3. As shown in the picture, the diver jumps upward. Why does he press down on the springboard?

Tip: The answer is from the perspective that the springboard deforms after being stressed and needs to restore the deformation to produce elasticity.

Reference answer: When a diver presses down on the springboard, the springboard bends and deforms under pressure. The deformed springboard pushes the athlete upward, causing the athlete to jump higher.

Exploration 2 Spring dynamometer

Combined with "experience", think about the following questions:

1. Analyze the stretching of the spring in activities 2, 3, and 4, and draw the conclusion: _______________.

Based on this property of the spring, force measuring tools such as _______________ are made.

Tip: The phenomena in activities 2 and 3 show that the greater the force, the greater the change in the length of the spring, that is, the longer it stretches; in activity 4, the pulling force is too large, damaging the spring and causing the spring to lose its elasticity, indicating that the spring can withstand The ability is limited; it can be concluded that within a certain range, the greater the tension on the spring, the longer it stretches. Based on this property of springs, spring dynamometers, grip dynamometers, tension gauges, etc. are made.

Reference answer: Within a certain range, the greater the tension on the spring, the longer it stretches. Spring dynamometer, grip dynamometer, tension meter, etc.

2. Point out the main parts of the spring dynamometer in the picture.

Reference answer: It is mainly composed of springs, hooks, pointers and dials.

3. Why do the numbers on the dial get bigger and bigger downwards?

Tip: Answer based on the manufacturing principle of springs. When it reaches the lower end of the dial of the spring dynamometer, the spring has the longest extension, and the greater the tension on the spring, so the numbers on the dial get larger as it goes downwards.

Reference answer: The greater the tension on the spring, the longer it stretches.

Knowledge summary

1. Elasticity

1. Elastic force: The force generated by an object due to ________. Such as pressure and support.

2. Elastic deformation: An object will ________ after being subjected to force. After the force is removed, the object can deform ________.

2. Spring dynamometer

1.Purpose: To measure _________.

2. Structure: (as shown in the picture)

3. Principle: When the spring is stretched within ________, the greater the tension on the spring, the elongation of the spring will be _____.

Test Points Measuring force with a spring dynamometer

[Typical example] (2012·Dali High School Entrance Examination) The indication of the spring dynamometer in the picture is _________N.

[Idea Guide] The key to solving the problem: clarify the range and graduation value of the spring dynamometer, and observe the position of the pointer.

[Concise Lecture and Analysis] This question tests the reading of the spring dynamometer. The measuring range of the spring dynamometer in the picture is 0~6N. One large grid of the spring dynamometer represents 1N, and there are 5 small grids inside. One small grid represents 0.2N, that is, its graduation value is 0.2N. Therefore, the indication of the spring dynamometer is 3N+1×0.2N=3.2N.

Answer: 3.2

[Method Summary] How to read spring dynamometer

1. The picture shows the event icon of the 2012 London Olympics. In the following competition scenarios, elasticity is not applied to ()

[Analysis] Choose B. This question tests your understanding of elasticity. When a diver jumps off a springboard, the springboard's elastic force exerts on the athlete. Swimmers move forward in the water using the principle that the forces between objects are mutual. Archery athletes rely on the elasticity of the bow to shoot arrows. The lift of trampoline athletes from the trampoline is accomplished by the elasticity of the trampoline on the athletes. So choose B.

2. The process of measuring force using a spring dynamometer involves the following operations:

① Gently pull the hook back and forth twice.

②Add the force to be measured on the hook.

③Observe the measuring range of the spring dynamometer and find out its scale value, that is, how many cattle each small grid represents.

④Adjust the pointer position of the spring dynamometer.

⑤Read the number after the pointer stabilizes.

The correct order for the above operations is ()

A.①②③④⑤ B.②③④①⑤

C.④①②③⑤ D.③④①②⑤

[Analysis] Choose D. This question mainly tests the correct use of spring dynamometer. When using a spring dynamometer, follow the sequence of first observing, then adjusting, and then measuring.

3. The picture shows several students using a spring dynamometer. The wrong measurement method is ()

[Analysis] Choose D. This question tests the correct use of a spring dynamometer. When using a spring dynamometer to measure the force, the direction of the force must be along the axis of the spring dynamometer. Items A and B are correct; item C measures the pulling force on the object when the object is pulled up along the incline. The method is Correct; the direction of the force being measured in item D is not along the axis of the spring dynamometer, and the hand also blocks the display of the dynamometer. Item D is wrong.

Find out where you tend to go wrong?

As shown in the picture, what is the reading of the spring dynamometer?

[Students’ own answers]

400N

[Teacher Comments]

① Analyze that the spring dynamometer is subjected to two forces, which is correct.

②Error: Not understanding the reciprocity of power.

【standard answer】

200N

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Update Time: 2024-06-30

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