"Synthesis of Two Forces on the Same Straight Line" Motion and Force PPT Courseware 3

Description

"Synthesis of Two Forces on the Same Straight Line" Motion and Force PPT Courseware 3

learning target

1. Understand the concept of combined force.

2. Understand the synthesis of two forces on the same straight line; be able to flexibly use it to analyze and solve simple problems.

1. Resultant force and synthesis of force

When several forces act together on an object, their effect can be replaced by one force, which is called the resultant force of those forces. If the magnitude and direction of several forces are known, finding the magnitude and direction of the resultant force is called the synthesis of forces.

For example: two children can lift a bucket, and an adult can also lift it. Then the force of the adult to lift the bucket is the combined force of the two children to lift the bucket. In turn, the force of the two children to lift the bucket is the force of the adult. Two components of the force carrying the bucket. Therefore, the resultant force and component force are based on "equivalent substitution".

If a force produces the same effect as two forces acting together, the force is called the resultant of those two forces.

2. The resultant force on the same straight line.

Force not only has magnitude, but also direction. The resultant force of two forces is not only related to the magnitude of the two component forces, but also related to the direction of the two component forces.

When two forces acting on the same object on the same straight line have the same direction, the magnitude of the resultant force is equal to the sum of the two forces, the direction of the resultant force is the same as the direction of the two forces, and the resultant force is greater than any of the component forces.

When two forces acting on the same object on the same straight line have opposite directions, the magnitude of the resultant force is equal to the difference between the two forces, and the direction of the resultant force is the same as the direction of the larger force. If the two forces are equal in magnitude at this time, the resultant force is zero and is smaller than any of the component forces.

It can be seen that the resultant force can be greater than any component force, or it can be smaller than any component force, or it can be greater than one of the component forces and less than the other component force.

Analysis of typical examples

For example, if a person lifts a 250N object vertically upward with a force of 300 N, what is the resultant force on the object? What is the direction?

Analysis: The resultant force of two forces is required to be performed in the following order.

① Determine whether these two forces act on the same object.

② Determine whether the directions of the two forces are the same or opposite.

③ Calculate the magnitude and direction of the resultant force according to the synthesis method of the same direction or the opposite direction. The answer to this question is that the pulling force F is in the opposite direction to the object's gravity G;

The resultant force F=F-C=300 N—250 N=50 N;

Resultant force direction: vertically upward.

feedback reinforcement

1. If a force produces the same effect as two forces, the force is called the _____ of the two forces.

2. A spring balance is used to pull an object upward. The indication of the spring balance is 10 N, and the gravity of the object is 8 N. The resultant force on the object is _____N, and the direction is _____.

3． An object weighing 10 N is placed on a horizontal table, and a 100 g weight is placed on the object. At this time, the pressure on the table is _____N.

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Update Time: 2024-07-22

This template belongs to Physics courseware Beijing Normal University eighth grade physics volume 2 industry PPT template

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