"Motion and Stillness" Simple Movement of Matter PPT Courseware 6

Description

"Motion and Stillness" Simple Movement of Matter PPT Courseware 6

Key points focus on test points

The test points covered in this class include: the conditions for the balance of two forces, how an object moves under the action of a balancing force, the understanding of Newton's first law, understanding of inertia and being able to use inertial phenomena to explain daily life phenomena, and the synthesis of two forces on the same straight line. Objects Changes in motion state under the action of unbalanced forces. Judging from the questions in the high school entrance examination, the above test points mostly appear in the form of fill-in-the-blank and multiple-choice questions. The synthesis of two forces on the same straight line may appear in the form of drawing questions, such as drawing a diagram of the composite force of an object. The derivation of Newton's first law may appear as an experimental question. This lesson focuses on connecting the force on an object with its motion. The object's motion will be judged based on the force on the object, and conversely, its motion will be judged based on the object's motion. Stress conditions.

Warm up before class

1. An object is in equilibrium means that the object is in a ____ state or a __________ state.

2. As shown in Figure 4-3-1, the object that can be in a stationary state is __ in the figure.

3. A middle school student with a mass of 50 kg is standing still on the ground. He is acted upon by __ force and ____ force. The objects exerting these two forces are ____ and ____ respectively. These two The relationship between forces is ________.

4. Someone uses a horizontal pulling force of 40 N to the right to pull a weight of 100 N to move in a straight line at a uniform speed on the horizontal plane. The speed is 1 m/s. Then the sliding friction force between the weight and the ground is __ N, the direction is ____; when the weight makes a uniform linear motion to the right at a speed of 0.5 m/s on the same horizontal plane, the sliding friction force between the weight and the ground is ___ N, and the direction is left , the resultant force on the object at this time is __N.

5. The magnitudes of the two forces on the same straight line are F1=15 N and F2=20 N respectively. If the directions of the two forces are the same, the resultant force is __ N; if the directions of the two forces are opposite, the resultant force is The magnitude is __N and the direction is the same as the direction of ___ force.

Analysis of typical examples

[Example 1] An ink bottle is placed on a horizontal table. When it is stationary, which of the following pairs of forces is a balanced force ( )

A. The pressure of the ink bottle on the desktop and the support of the desktop on the ink bottle

B. The gravity of the table and the support force of the ground facing the table

C. The gravity of the ink bottle and the pressure of the ink bottle on the table

D. The gravity on the ink bottle and the support force of the table on the ink bottle

[Example 2] As shown in Figure 4-3-3, a car is placed on a level ground with a smooth surface. Two small balls with masses m1 and m2 (m1＜m2) are placed at rest. When the car suddenly When moving to the left from rest, two small balls ( )

A. The relative car moves to the left, and the speed of m2 is greater than the speed of m1, and the two balls move closer.

B. The relative car moves to the right, and the speed of m2 is greater than the speed of m1, and the two balls move closer.

C. The relative car moves to the right, and the speeds of m1 and m2 are equal

D. It is stationary relative to the car and moves to the left with the car.

Method summary

The equilibrium state of an object means that the object is at rest or moving in a straight line at a uniform speed. The resultant force on the object in the equilibrium state is zero. The conditions for the balance of the two forces are: congruent, equal, opposite, and collinear. The lack of one of the four is different. , the resultant force is zero. If one component is known, the other component can be found, because F1 = F2. When finding the resultant of two forces on the same straight line, first determine the direction relationship between the two components, and then perform the calculation. , when the direction of the component forces is the same, F sum = F1 + F2, the direction of the resultant force is the same as that of F1 and F2. When the direction of the component forces is opposite, F sum = F1-F2 (F1>F2), the direction of the resultant force is the same as the direction of the largest component force. The same. Determine the motion state of the object according to the force on the object. The specific rule is: when the object is subject to a balance force or is not acted upon by an external force, it is still stationary. It is originally in motion and will move in a straight line at a uniform speed. When the object is in motion, it will move in a straight line at a uniform speed. When acted upon by an unbalanced force, the object's motion state must change. If the direction of the resultant force is the same as the direction of motion, the object will accelerate. If the direction of the resultant force is opposite to the direction of motion, the object will decelerate. If the direction of the resultant force is not in a straight line with the direction of motion, The object moves in a curve. The force is determined according to the movement of the object.

Class training

1. An iron block weighing 10 N is placed at rest on a horizontal ground. The force supported by the ground is __ N, and the resultant force it receives is __ N.

2. As shown in Figure 4-3-7, a car weighing 5 N is placed on the horizontal ground. The horizontal force to the left is F1 and the horizontal force to the right is F2. Then the resultant force on the car in the horizontal direction is ___ N, direction________, the resultant force in the vertical direction is __ N.

3. In a moving car, there is a small ball hanging. If the ball swings in the direction of travel, it means that the speed of the car is ____ (fill in "get bigger", "get smaller" or "unchanged"). If it is small The ball swings to the right, indicating that the car is turning in the __ direction.

4. Hang an object with a mass of 1 kg on the hook of the spring dynamometer. When the object is stationary, read the reading of the spring dynamometer as ___N; if the spring dynamometer is held at 0.1 m/ If the spring dynamometer makes a uniform straight line motion upward at a speed of 0.2 m/s, then the reading of the spring dynamometer is ___ N; if the spring dynamometer makes a uniform straight line motion downward at a speed of 0.2 m/s, then the reading of the spring dynamometer for ___ N.

5. Hold the oil bottle in the air with a force of 20 N. If the grip force of the hand is increased to 30 N, the friction force between the hand and the oil bottle will ____(fill in "increase" ”, “decrease” or “unchange”).

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Update Time: 2024-10-12

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