"Newton's First Law" Motion and Force PPT Courseware 6

Description

"Newton's First Law" Motion and Force PPT Courseware 6

Introduction of new courses

Since moving objects have the property of maintaining a uniform linear motion, why does a car moving at a uniform speed along a horizontal ground still need power?

Students think, why is this?

think

Does movement require force to maintain?

Aristotle's thought: If you want an object to continue to move, you must exert a force on it; if the force is removed, the object will stop moving.

Galileo's thought: Experiments have shown that the movement of an object does not require force to maintain it. The reason why the movement stops is due to the action of frictional resistance.

Which statement is correct?

Observation and Experimentation

Experimental design purpose: To explore whether the movement of an object requires force to maintain

Experimental design idea: Take the car as an example, try to minimize the impact of force on the movement of the car, and observe the movement of the car. (How to make the car move farther?)

The same conditions: the same car, the car starts moving at the same speed (the same slope, stops at the same height and starts to slide)

Different conditions: different surfaces mean different resistances

Experimental equipment: wooden board, trolley, cotton cloth, towel, slope

Experimental methods: controlled variable method, ideal experiment method

Newton's first law

Galileo's Thrust: If the surface is relatively smooth and the resistance to the object is zero, the object will not move at a constant speed and will continue to move at a constant speed forever.

Newton's first law: All objects always remain at rest or move in a straight line at a uniform speed when no force is acted upon. Also called the law of inertia.

Law interpretation

1) "Newton's first law" expresses the law of motion of an object when there is no force.

2) The motion of an object does not require force to maintain it.

3) Force is what changes the state of motion of an object

4) Newton's first law is not an experimental law.

Notice

1) All objects

Refers to all objects in the universe, whether solid, liquid or gas. It can be seen that Newton's first law is a universal law in nature.

2) Not affected by external force

is the condition for the establishment of the law, which is an ideal situation

3) time

It emphasizes the instantaneous correspondence between "not being acted upon by force" and "maintaining a state of rest or a state of uniform linear motion". When an object is not acted upon by an external force, the object remains in a state of rest or in an instantaneous state of uniform motion in a straight line.

4) Always means "always".

5) Maintain means "unchanged".

6) Or refers to an object that can only be in one state. Which state it is in is determined by the original state. If it was originally stationary, it will remain stationary, and if it was originally moving, it will maintain a state of uniform linear motion.

Typical examples

[Example 1] A small ball is tied with a rope and moves in a circular motion on a smooth horizontal surface. When the rope suddenly breaks, the small ball will [ ]

A. Maintain the original circular motion.

B． Keep the speed at which the rope was broken and move in a straight line at a constant speed.

C. The speed of the ball decreases but remains straight.

D． All three of the above are possible.

[Analysis] It turns out that the ball is moving in a circle due to the tension of the rope. When the rope suddenly breaks, the ball no longer receives force in the smooth horizontal direction, so the ball will keep the speed and direction at the moment when the rope breaks.

【Answer】B

[Example 2] The following statement is correct: [ ]

A. An object must be at rest if no force acts on it.

B． If an object is not acted upon by any force, it must move in a straight line with uniform velocity.

C. Objects can move only when they are acted upon by force.

D． The above statements are all wrong.

[Analysis] Newton's first law states that when an object is not acted upon by an external force, it will remain at rest or move in a straight line at a constant speed. It shows that objects can have two states of expression, and it also shows that objects can move without force. Force is not the reason for maintaining the motion of objects.

Practice in class

1. Regarding the relationship between force and motion, which of the following statements is correct ( )

A. Objects move only when they are acted upon by force

B. Force changes the motion state of an object

C. Stop exerting force and the moving object will stop.

D. Force is what keeps an object at rest or moving in a straight line at a uniform speed.

2. If the external force on a moving object suddenly disappears, it will ( )

A. Stop immediately

B. The speed decreases and finally stops.

C. The direction of movement becomes opposite to the original one

D. Make uniform linear motion

3. If the object is not affected by external forces, which of the following statements is correct ( )

A. A stationary object remains stationary forever.

B. Moving objects will not stop

C. The object’s motion state will remain unchanged

D. The object will maintain uniform linear motion or be at rest.

4. If an object is moving in a straight line at a constant speed and is suddenly acted upon by an external force, will its state of motion definitely change?

Analysis: The original motion state of the object is a uniform linear motion, and the corresponding force situation is "no force" or "the resultant force is zero". On this basis, an external force is applied to the object. At this time, the resultant force on the object must not be zero, and the motion state of the object will definitely change.

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Update Time: 2024-09-07

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