High School Physics Common Point Force Problem, High School Physics Common Point Force

This question is extremely simple, which shows that the basic knowledge is not solid.

Just look at Newton's first law and you'll know that it's wrong.

In an inertial frame, all objects always remain in a state of constant linear motion or a state of rest until an external force forces it to change this state.

Note the inertial frames in it. In a non-inertial frame, the velocity of an object can always be zero, but it is not balanced by forces.

Note the "total", even in the inertial frame, the velocity of the object is zero at a certain moment, which does not mean that the force is balanced.

This is called the law of physics, and it is extremely strict. Read the laws you have learned carefully, and you will be rewarded. All the knowledge in the book revolves around the laws of nature.

But if you understand enough, you don't need anything. Just say the theorem and the law will make everything clear.

Not necessarily, when a stationary train starts moving, its velocity is 0, but the resultant force it exerts is not 0.

Not necessarily. There may be acceleration.

It just happened to be 0.

For example, throwing a small ball upwards.

The velocity is 0 at the highest point

But it's not balanced.

Only by gravity.

The equilibrium state refers to: stationary or uniform linear motion, both states have one thing in common, that is, the acceleration is zero, so it can be said that the criterion for judging whether it is in an equilibrium state is whether the resultant external force on the object is zero and whether the acceleration is zero.

For example, an object moves at a uniform deceleration, and then moves in the opposite direction, when its velocity is exactly zero, the force on the object is unbalanced, and the acceleration is not zero.

No, there may be force when decelerating to zero. The imbalance of the object is seen from the state of motion.

Constant motion and stationary forces are balanced.

This view is wrong.

Let's say rocket launches.

At the beginning, the speed is 0

But the acceleration is surprisingly large.

And the so-called equilibrium is created under the condition that the resultant force is zero.

The system has acceleration, and the system must be unbalanced.

Is an object moving at zero velocity necessarily in equilibrium?

Answer: An object with zero velocity is not necessarily in equilibrium.

Study the entire system (except for the walls).

The system is in equilibrium throughout the process, and the force in its vertical direction is investigated.

In the vertical direction, only the gravity of the ball (unchanged) and the vertical component of the AB rod by the elastic force of the wall (along the AB direction).

So the magnitude of this component should be equal to the gravitational force of the ball. The pressure on AB can only be in the direction of AB (otherwise the force on AB is unbalanced). The direction of a force does not change, its vertical component does not change, and it can be pushed out of its own magnitude as well.

Rummy Principle.

If the net force of the three commonalities is zero, then a triangle can be formed by translation, because the ball is balanced by force.

Point b is balanced by force.

The elastic force of the rod is along the elastic force of the AB rope.

The pull of bf.

The pull of BC.

Translate it to form a triangle.

The length of the edge corresponds to the magnitude of the force.

The direction of the edge corresponds to the direction of the force.

The length of the rod doesn't change, so the amount of elasticity on the rod doesn't change either.

Solution: The answer is CSo the answer upstairs is wrong.

When the block is at point B, let the elongation be m, then the spring tension is km, when the block runs to point C, let the angle between the spring and the horizontal direction be n, then the spring elongation is m sin(n), and the spring tension is km sin(n), then the component of the spring tension in the vertical direction is (km sin(n))*sin(n)=km

Therefore, from the above analysis, it can be seen that the tensile force of the spring in the vertical direction is always km, so the pressure of the block on the ground is also constant, and the frictional force is also unchanged.

C just read wrong.

Excuse me. f= n n = mg k x sin (is the angle between the rubber cord and the horizontal) while k xsin = k is unchanged. So f does not change. Therefore c is correct.

f=un,n=mg-t1=mg-tsin f=u(mg-tsin), the elongation of the rubber rope is proportional to f, if the elongation is s, t=ks sin, f=u(mg-ks) c

The height difference between the two is l. A lightweight, non-extendable string is fixed at point A at one end and the other.

The end is suspended from a weight of mass m1 across a smooth nail b. At point C of the rope from end A.

There is a fixed rope loop. If the hook code with a mass of m2 is suspended on the rope loop, the AC section of the rope after balancing is positive.

At a good level, the mass ratio of the weight to the hook is ( root number 5 2) <>

Because the forces are balanced, you arbitrarily combine two forces to be the third force and other forces in the opposite direction!

It's okay to be able to pass a picture.。。。

The direction of the tension of the rope is along the rope, but the direction of the support force of the stem is not necessarily along the direction of the rod.

The resultant force that is subjected to multiple common point forces is 0The magnitude of one of the forces is 10 N.

Explain that the remaining force is in the opposite direction to the magnitude of this force.

Now rotate this force 90 degrees clockwise, leaving the other forces the same.

It is a combination of a force of 10n negative to the y-axis and a force of 10n negative to the x-axis.

The magnitude of the resultant force is (10*root number2)n

The direction is negative with the y-axis, and the x-axis is negative at 45 degrees (third quadrant), I hope it can help you!

Note: The title allows you to find the "pull", vector, and be sure to indicate the size and direction.

At this moment, it can be regarded as a balance of forces! The cargo can be regarded as a particle, which is subject to three forces: the vertical downward gravity, the vertical contact surface support force, and the rope tension.

Three-force equilibrium, orthogonal decomposition, simultaneous equations, and the solution is solved. I won't repeat the answer if someone gives me.

The techniques for force analysis are the first field force (gravitational field, electric field, magnetic field), the post-elastic force (support force, spring force), and finally the frictional force and the like (because it is the most difficult to determine). Grasp the principle, and don't be afraid of any question type. If the force is balanced, it is the same as the above solution.

If there is acceleration, use the resultant simultaneous equation.

The sliding friction force given by A to B is f= GA=2N

B has a constant velocity, then A is also at a constant velocity, A is subjected to rope tension f1 = g = 2n, so b is subject to rope garbage f2 = f1 = 2n

b is subjected to the frictional force given by the ground f2 = (ga+gb)=6nf=f+f2+f2=2n+2n+6n=10n

Take advantage of angle relationships.

Then calculate the resultant force and find the relation between them, and the root number 6 2 should be chosen

Regardless of the magnitude of the directional force, f1 = f2 = (f divided by the root number 2).

At an angle of 60° (f divided by root number 2) multiplied by root number 3, it is good.

Choose b because f1 = f2, when the angle is 90°, the resultant force is: root number 2) * f1 = f

Get f1 = root number 2) 2) f

When the angle between f1 and f2 is 60°, the resultant force is (root number 3) * f1 = root number 6) 2) * f.

The triangle rule is to translate (the current force synthesis is basically a common point force), the beginning of a force is translated to the end point of another force, from the beginning of the force that has not been translated to the end of the force that is translated is the resultant force, and the synthesis of force has the law of parallelogram!

In the synthesis of forces, it will have an impact on whether a force can be translated to a certain position and then synthesized.

In the calculation of forces, the same plane can be translated without any effect. The synthesis of forces requires the understanding of how to analyze the meaning of the problem and transform it into graphs, be familiar with graph analysis, and be able to use some theorems in mathematics to make inferences.