"Newton's First Law" Motion and Force PPT Courseware 7

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"Newton's First Law" Motion and Force PPT Courseware 7

1. Force is what changes the state of motion of an object

The perspective of the ancient Greek scholar Aristotle - maintaining motion requires force

If an object is to continue to move, a force must be exerted on it. If this force is removed, the object stops moving.

Italian scientist Galileo's point of view - no force is needed to maintain motion

The motion of an object does not require force to maintain it. The reason why the motion stops is because of frictional resistance.

Reasoning: If a moving object receives no force, it will move in a straight line at a constant speed (move forever at a constant speed)

Ideal state: If the surface is absolutely smooth, the resistance to the object is zero.

2.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.

explain:

The object is not subject to external forces or the sum of the external forces is zero: a state of rest or a state of uniform linear motion (equilibrium state)

The object is subject to an external force and the sum of the external forces is not zero: the object changes state of motion

1. Contents of 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.

Notice:

(1) Newton's first law is obtained by analyzing facts and then further generalizing and reasoning.

(2) Newton's first law clarifies the relationship between force and motion. Therefore, force is the reason for changing the motion state of an object, not the reason for maintaining the motion of the object.

3.Inertia

All objects have the characteristic of maintaining their original state of motion under any circumstances.

All objects: solid, liquid, gas

Inertia is an inherent property of an object.

Any situation: stationary or moving, fast or slow, constant speed or variable speed...

Motion state: stationary, uniform linear motion

Please explain using inertial knowledge:

When a car brakes, the soles of the person's feet stop due to friction. The person's upper body will continue to move forward due to inertia, so when braking or decelerating, the person will lean forward.

So what does the car do in the picture below?

When a car accelerates, the soles of the person's feet become stationary due to friction, and the person's upper body still maintains its original slow-speed motion due to inertia, so when accelerating, the person will lean back.

Summary

1. Contents of 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.

Note: (1) Newton's first law is obtained by analyzing facts and then further generalizing and reasoning.

(2) Newton's first law clarifies the relationship between force and motion. Therefore, force is the reason for changing the motion state of an object, not the reason for maintaining the motion of the object.

2. Inertia:

The property that an object maintains its original state of motion is called inertia.

Notice

(1) Inertia is a property of objects. All objects have inertia at any time and under any conditions. It has nothing to do with whether the object is subject to force, whether it is moving, whether the state of motion changes, etc.

(2) Inertia is not a force. It cannot be said to be "inertial force", "inertial force", "inertial action" or "an object is subject to inertia"

(3) The size of inertia is only related to the mass of the object. Objects with greater mass also have greater inertia.

3. Explain the phenomenon of inertia

(1) Analyze the original motion state of the research object

(2) Analyze who exerts force to change the state of motion

(3) Explain who maintains the original state of motion due to inertia

(4) Finally explain what happened

Consolidation exercises

Regarding inertia, which of the following statements is correct ( )

A. The property that all objects always maintain a state of uniform linear motion or rest when not acted upon by external forces is called inertia.

B. The fired bullet leaves the muzzle and continues to move forward at high speed because the bullet is affected by inertia.

C. The car can continue to move forward after turning off the engine because the car's inertia is greater than the resistance it encounters.

D. All objects have inertia under any circumstances.

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Update Time: 2024-09-07

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