The synthesis of physical forces in high school, the synthesis of physical forces in high school

If you don't know much about this, you really have to draw a diagram, because it is a regular hexagon, so there are many properties of plane geometry that can be used.

As for the resultant force part of physics, it is enough to apply the parallelogram rule, or the triangle rule.

To put it simply, the resultant force of f and f is to translate the force f, that is, the line segment of of, so that the o' point and f coincide. Then the 'line segment is the direction and magnitude of the resultant force.

After translating according to the law of triangles, you can use the angle to calculate, but you are not doing it very well.

The resultant force of f2 and f5 should be taken (i.e., f5 should be shifted to the dotted line between f2 and f3) so that at a glance the resultant force of f2 and f5 is equal to f3

In the same way, the resultant force of f1 and f4 is equal to f3

So the sum of these five forces is three times f3

Hope it helps

This is already a math problem.

Pro, the vector synthesis of f1 and f5 is a multiple of f3, which is in the same direction as f3;

The vector synthesis of f2 and f4 is a multiple of f3, which is in the same direction as f3;

It adds up to 3 times f3

From the synthesis of forces, the law of parallelograms can be known. Combined with the graphic properties of a regular hexagon. It can be obtained.

Translate the force to get the parallelogram.

It can be obtained by drawing, and it is very simple to use vector determination.

1. Select people as the research object, people are subjected to three forces, gravity, and the pull of the arm to the person is not parallel, there are angles. When the gravity is constant and the angle is not zero, the angle between the arm and the vertical plane is &

mg=2fcos&

Because cos&<1, F greater than mg2 is not the minimum.

2. This is the same as the previous question.

When the angle becomes smaller, the net force of the rope increases, so c pairs.

1. The first question should choose B, when the two forces are combined, the colinear co-directional resultant force is the largest; Now the resultant force is a certain weight g of the person, then the two components are naturally collinear and the smallest in the same direction at this time; Hence B

It can also be synthesized according to the two-force method mg=2fcos&, when &=0 cos&=1, at this time the maximum, then f is the smallest.

b only increase the weight of the weight c move the fingers down.

It can be explained by the composite relation of two equal forces f=2mgcos&, only moving the finger downwards then & decreases and cos& increases; f also becomes larger.

Only the weight of the heavy object is increased, m increases, and f also increases.

Do you understand? I hope it helps.

A is not a 90-degree vertical upward pull, B is.

Question 2 selects B and C

It's not easy to draw.

Question 1: In option A, the hands are too close together and there is a certain angle between the arms, so the force on each arm is greater than half of its own gravity when the pull-ups are pull-ups.

Question 2: Option A, increase the length of the thin line if it is only the length between the weight and the fixed pulley, the angle

It doesn't change, so the force on the fingers doesn't change; Option d: The angle becomes larger, and the force on the finger decreases; Option b The angle remains the same, but the weight becomes heavier and the fingers are stressed; Option C becomes smaller, and the force on the fingers increases.

3 All Answers: a, c

Use the triangle rule.

F1 is 30 degrees to f, what is the size?

f2 is the magnitude (root number 3 3) f, direction?

And because: fsin30=f 2< (root number 3 3)f. There are two solutions.

Then solve it with mathematical knowledge.

If you don't understand, I'm writing in detail.

- -Now that you're a freshman in high school, you'll learn vectors.

Directly use the addition and subtraction of vectors to make a triangle of force, knowing the force is equivalent to knowing the length of the line segment.

The angle is equal to the angle of the force, and that's it.

6f ...... correctly

It is easy to get F3=2F, and the resultant force of F1 and F4 is F3, and the resultant force of F2 and F5 is also F3, so the resultant force of F1, F2, F3, and F4 and F5 is 3 F3, that is, 3*2F=6F

Answer: BC

I drew 4 drawings for you, please wait for review.

Proof: Nowhere is it most evident with the triangular rule.

Draw f1 and f2 so that f1 and f2 follow each other.

When the angle is 0°, the resultant force f will increase if f1 and f2 increase.

When the angle is obtuse (as is the right angle).

a. When the small force F2 increases, F increases first and then decreases; (There will be a situation where f does not change) b. When the vigorous force f1 increases, f must increase.

When the angle is an acute angle, whichever increases f1 and f2, the resultant force f must increase.

When the included angle is 180°.

a. When the small force F2 increases, F decreases first and then increases; (There will be a situation where f does not change) b. When the vigorous force f1 increases, f must increase.

There will be a situation where f does not change" The figure can be seen, and I will say the following.

For example: f1 = 10n f2 = 5n

Then the magnitude of the resultant force is f1 - f2 = 10-5 = 5n and if f2 becomes 15n, f1 = 10n

The magnitude of the resultant force is f2 - f1 = 15-10 = 5na The magnitude of the resultant force f must increase (

b The magnitude of the resultant force f may not change (

c The resultant force f may be larger or smaller (

d When zero degrees < ninety degrees, the magnitude of f must increase (

Take the angle between f1 and f2 at 127° (180-53) as an example. If f1 = 3n and f2 = 5n, then f is 4n. At this point, increase or decrease f1, and f will both increase. and bc correct.

In the d answer, the two forces are connected end to end to form an obtuse triangle, and the resultant force is the length of the opposite side of the obtuse angle. Therefore, if f is greater than f1+f2, then f1 increases and f also increases.

The final answer is BCD

cd, draw a parallelogram, f1f2 is the adjacent sides, f is a diagonal.

cd This is not easy to explain... I can only draw pictures and consider different situations...

This method is particularly convenient for the synthesis of more than two forces, as shown in Figure C, where the point p is affected by the four common point forces of F1, F2, F3 and F4, and their resultant forces are found. It is possible to translate the forces one by one and connect them head to tail.

Because it is a constant downward spiral, m,n are in equilibrium.

It is subjected to gravity by all means, so it is subjected to elastic force and friction force of n (along the inclined direction) to balance it.

n The whole is subject to gravity in order to balance, so it is also supported by friction (along the inclined plane) and inclined planes.

3.As there is no acceleration in the inclined plane and m,n as there is no acceleration, it is in equilibrium and is only supported by gravity and the ground.

To sum up, select the db option, the slider is subjected to friction along the inclined plane, and the inclined plane is driven downward by the frictional force of the slider along the inclined plane.

As for the C touch, I didn't touch the force from anywhere.

AD's center of gravity shifts to the left, so it is affected by elastic force.

m balance, so the friction force is upward along the inclined plane.