"Force" Motion and Force PPT Courseware 2

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"Force" Motion and Force PPT Courseware 2

All objects always remain at rest or move in a straight line at a uniform speed when no force is acted upon.

1. How to seek synergy

1. When the directions are the same

2. When the direction is opposite

Introduction of phenomena

1. Keep the textbook still on the table.

2. A skydiver falling at a constant speed.

3. Hanging electric lights.

4. A car that moves in a straight line at a constant speed.

New course teaching

(1) Balance of forces

If an object remains at rest or moves in a straight line at a uniform speed when acted upon by several forces, we say that these forces are balanced. The state the object is in at this time is called equilibrium state. If an object is acted upon by only two forces and is in equilibrium, this situation is called two-force equilibrium.

Demonstration experiment 1

Hold the wooden block still with your hand and add different hook codes on both sides. After letting go, you can see that the wooden block accelerates towards the side with more hook codes.

Hold the wood block still with your hands, add equal hooks on both sides, and when you let go, you can see: the wood block is still. (is a state of equilibrium)

Conclusion: Only when the two forces on an object are equal in magnitude can it continue to maintain a state of equilibrium.

Demonstration experiment 2

Hold the wooden block still with your hand, tie two strings to the same side of the wooden block, and hang equal hooks on the two ropes. After you let go, you can see that the wooden block moves in the direction of the force.

Conclusion: The two forces on an object must be in opposite directions to maintain equilibrium.

Demonstration experiment 3

Rotate the wooden block by hand to a certain angle and hang equal hooks on both sides so that the two forces do not act on the same straight line. After letting go, you can see that the wooden block is rotating and cannot be balanced.

Conclusion: The two forces on an object must act on the same straight line for the object to be balanced.

Note organization

1. Calculation of resultant force

When the direction is the same

When the direction is opposite

2. Two force balance conditions: congruent, collinear, opposite, equal magnitude

3. The state of an object under the action of a balancing force: it always remains in a ______ state or a __________ state

Application of two force equilibrium conditions

1. Please draw a schematic diagram of the force on the object in Figure 9-3-2.

And analyze whether the object is subject to a balancing force and which pair of forces is a two-force balance.

1) Stationary hanging electric lamp.

2) The teacup resting on the table.

3) A trailer moving at a constant speed.

2. Which of the following four figures reflect the balance of two forces?

4. Exercise in a clear and dignified manner

1. The wooden block placed on a horizontal table is at rest. Which of the following pairs of forces is a balanced force ( )

A. The gravity of the wooden block and the pressure of the wooden block on the tabletop

B. The pressure of the wooden block on the tabletop and the support of the tabletop on the wooden block

C. The gravity of the wooden block and the support force of the tabletop on the wooden block

D. The gravity of the wood block and the attraction of the wood block to the earth

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

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

3. Someone is holding a fish stationary with a rope. At this time, the balancing force on the fish is the pair of ____________ and ____________.

4. When the hook code hanging on the spring scale is at rest, the two forces that balance each other for the hook code are ____________.

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For more information about the "Movement and Force" PPT courseware, please click the "Movement and Force ppt Force ppt" tab.

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Update Time: 2024-11-25

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