"Two Force Balance" Force and Motion PPT Courseware 2

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"Two Force Balance" Force and Motion PPT Courseware 2

Observation: When the car is at rest, is it affected by external forces?

Observation: The plane can maintain uniform linear motion in the air. Does it receive any force?

1. Equilibrium state: When an object is acted upon by two (or more) forces, it can remain stationary or move in a straight line at a uniform speed. We say that the object is in a state of equilibrium.

Balanced state

Stationary state

Uniform linear motion state

2. Balance force: Two forces (or forces) that keep an object in equilibrium.

3. Two-force balance: If an object is in equilibrium due to only two forces, this situation is called two-force balance.

Is the following situation an equilibrium state:

child swing

Raindrops fall vertically at a constant speed

Pencil box stationary on the desk

Running second hand

Plane flying horizontally and at constant speed

Take a guess

Ask a question: When the two forces acting on an object meet what conditions can the object remain stationary?

Conditions for balance of two forces

Experimental exploration

Ask the question: What kind of force does an object have to be in equilibrium?

Conjecture, hypothesis:

A. The two forces are equal in magnitude and opposite in direction.

B. The two forces are on the same straight line, and the resultant force is zero.

C. Two forces act on the same object.

Experimental exploration

What are the conditions required for the balance of two forces?

Experimental conclusion: Conditions for the balance of two forces:

1. The two forces are equal in magnitude.

2. Opposite direction

3. Act on the same straight line

4. Act on the same object

Conditions for balance of two forces

Two forces acting on the same object balance each other if they are equal in magnitude, opposite in direction, and in the same straight line.

Application of two force balance

When using a spring dynamometer to measure the gravity of an object, it must be read when the object is stable.

The experiment explores what factors are related to sliding friction. When the object is made to move in a straight line with uniform speed in the horizontal direction

2. A pencil box is placed stationary on a horizontal table. Which of the following forces is a balancing force ( )

A. The pressure of the pencil box on the desktop and the support of the desktop on the pencil box;

B. The gravity of the pencil box and the pressure of the pencil box on the desktop;

C. The gravity of the pencil box and the support of the desk to the pencil box.

3. When the crane's wire rope lifts a heavy object, compare the pulling force of the wire rope on the heavy object when the heavy object is stationary, when the heavy object rises at a constant speed, and when the heavy object drops at a constant speed, then ( )

A. When the weight rises at a constant speed, the pulling force is maximum

B． When the weight is stationary, the pulling force is greatest

C. When a heavy object falls at a constant speed, the pulling force is maximum

D． In the above three cases, the pulling force is the same

4. True or false questions. (Pick “√” if it’s correct, “×” if it’s wrong)

(1) When an object is acted upon by a force, its state of motion must change. ( )

(2) When an object is not acted upon by force, its state of motion must remain unchanged ( )

(3) When a wooden box is pushed on a horizontal plane with a force of 5N, the friction force experienced by the wooden box is 5N. ( )

(4) The greater the speed of an object, the greater the resultant force it receives. ( )

(5) The state of motion of an object in a certain direction remains unchanged, and the resultant force it receives in this direction must be zero ( )

Summary of this lesson

1. Balance of two forces

When an object remains at rest or moves in a straight line at a constant speed under the action of two forces, we say that the two forces balance each other or the two forces are balanced.

2. Conditions for the balance of two forces (same object, equal magnitude, opposite direction, collinear)

Two forces acting on the same object must be equal in magnitude, opposite in direction, and act on the same straight line.

3. An object remains in motion under the action of a balancing force, that is, it always remains stationary or moves in a straight line at a uniform speed.

4. When an object is acted upon by an unbalanced force, its state of motion changes.

1. Use a spring dynamometer to pull an object weighing G twice to move vertically upward. The image of S-t during the two movements is as shown on the left. The corresponding spring dynamometer indications are F1\F2 and F1, respectively. F2, the size relationship is ( )

A F1

B F1=F2

C F1>F2

D All three of the above situations are possible

2. There are two objects A and B. They move in a straight line along the horizontal plane under the action of force. Its V-t image is shown in the figure. It can be seen from the figure that the force in the horizontal direction during the motion of the two objects is ( )

A. Both objects are acted upon by a balancing force

B. Neither object is acted upon by a balancing force

C. A is acted upon by a balanced force, and B is acted upon by an unbalanced force.

D. A is not affected by the balancing force, and B is affected by the balancing force.

3. As shown in the figure, a car is stationary on a horizontal road. An iron ball is fixed on the pole of its bracket. Regarding the direction of the force exerted by the pole on the iron ball, which of the following statements is correct ( )

A. Along the pole

B is perpendicular to the pole

C.Vertically upward

D. Along a certain direction between the pole and the vertical direction

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For more information about the "Force and Motion Two Force Balance" PPT courseware, please click on the Force and Motion ppt Two Force Balance ppt tag.

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Update Time: 2024-06-29

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