"How to Understand Force" Force and Machinery PPT Courseware 2

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"How to Understand Force" Force and Machinery PPT Courseware 2

Force There is force everywhere around us.

(a) Ants are carrying food

(b) A weightlifter lifts a barbell

(c) Crane lifting heavy objects

(d) Because the magnetic poles with the same name repel each other, the magnetic ring levitates.

How to recognize power

ants carry food

athlete lifts barbell

crane lifting heavy objects

Magnetic poles with the same name repel each other.

In physics, force is the action of an object on an object.

Activity 1: Study the effects of force

Analysis: The force-exerting object acts on the force-receiving object and the object changes (action effect)

1. Human hands pull the tensioner to lengthen the spring. The spring lengthens and changes its shape.

2. Tennis presses the racket, the racket’s net deforms, and the racket’s net string becomes concave and changes its shape.

3. The panda’s paws pull the bamboo pole, the bamboo trunk bends, and the bamboo trunk changes shape from straight to curved.

Conclusion: Force can change the shape of an object

The effect of force:

Force can cause an object to ___________; it can also cause an object to ___________.

Note: Changes in the motion state include changes in the speed and direction of motion. As long as one of the two changes, we say "the motion state of the object changes."

The effect that force can change the state of motion of an object can be clearly seen, and the effect of force that deforms an object is sometimes invisible to the eyes. Therefore, if the state of motion has not changed, it must have deformed.

Think about it: How do you tell if a force is acting on an object.

Criteria for the role of judgment:

There must be two or more objects

When an object is acted upon by a force, there must be another object exerting this effect on it.

Forced object: An object that is acted upon by a force

force-exerting object: object that exerts force

Are the effects of forces reciprocal?

Question: A takes the initiative to push B hard. How do A and B feel at this time?

A feels that B is pushing him, and B feels that A is pushing him.

How will A and B move?

A and B both move towards their backs

If B takes the initiative to push A hard, how will A and B feel?

How will A and B behave?

A and B both feel the same,

It’s also A who feels that B is pushing him,

And B feels that A is pushing him.

A and B both move towards their backs

Class summary:

1. Definition of force: Force is the effect of one object on another object.

2. When a force occurs, there must be an object exerting force and an object receiving force. Force cannot exist apart from objects.

3. Force is usually represented by the letter F, and the unit of force is Newton (N).

4. The effect of force: Force can deform an object and change its motion state.

5. The effects of forces between objects are mutual.

6. The size, direction and point of action of force are called the three elements of force. They all affect the effect of force.

3. Among the following examples, it cannot be said that "the effects of forces between objects are mutual" ( )

A. When swimming, you can move forward by paddling your hands and feet backwards

B. Throw the shot put from your hand

C. Pull the rubber band with your hand and feel that the rubber band is also pulling on your hand.

D. When jumping high, push down hard and the person can jump up.

4. Pull the elastic piece in the direction of the arrow with your hand to make it bend, as shown in the picture. It is known that the force in B, C, and D is the same, and the force in A is smaller.

Explain that the effect of force is related to the size of the force. Choose _________

Explain that the effect of force is related to the direction of the force. Choose _________

Explain that the effect of force is related to the point of action of the force. Choose _________

5. The three elements of force refer to __________, __, and __, and they all affect __________.

6. The student wearing roller skates pushed hard against the wall, and the student retreated. This phenomenon shows that __________, __________.

7. Short answer: When swimming, if you paddle backwards, you will move forward. Why?

Answer: When swimming, you paddle backwards and your hands and feet exert force backward on the water. Because the forces between objects are mutual, the water force exerts force on your hands and feet forward at the same time, making the person move forward.

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Update Time: 2024-11-21

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