The balance of the two forces can also make a uniform linear motion without the action of the third

Examples. When the skydiver moves in a straight line at a uniform speed in the air, the gravity and resistance are balanced, since the gravity and resistance are balanced, then the skydiver should be stationary, is the two forces balance theorem wrong?

Answer: This is explained by Newton's first theorem, which is the theorem of inertia: when an object is not subjected to an external force, or the sum of the external forces is zero, the object always remains at rest, or moves in a straight line at a uniform speed.

Because, when the parachutist just jumped out of the plane window, he has a certain initial velocity, and begins to parachutist to make a uniform acceleration linear motion, and with the increase of his speed, the corresponding air resistance also increases, the air resistance is proportional to the speed, when the resistance and gravity are equal, the two forces balance is reached, therefore, the parachutist continues to maintain the original speed of the two forces balance to move in a uniform straight line, therefore, the parachutist is not stationary.

According to Newton's first law, also known as the law of inertia, it can be known.

The motion of an object does not require force to maintain, force is to change the state of motion of the object.

When the external force of the object is 0, it must be in a state of stationary or uniform linear motion.

An object with a resultant external force of not 0 must be in accelerated motion.

Because in constant motion, there is no resistance, no stop, no thrust, no fast, it's as simple as that.

It is known from Newton's first law.

Anything goes.

Maintain a uniform linear motion or stationary.

In the absence of force.

Anything goes.

Maintain a uniform linear motion or stationary.

1.An object always retains its original motion when it is subjected to two forces of equal size, opposite directions, and acting at the same point.

Analysis: If the object is in motion when the two forces are in equilibrium, then the object is not affected by external forces, and it maintains this state of motion.

When you refer to the force that is greater, then the movement is moving, and that refers to the situation when the state of motion changes, such as from stationary to motion, that is, which side has the greater force and which side it is facing.

2.This question is the same as above, if the raindrop is moving at the beginning, then the balance of the two forces only means that his state of motion does not change.

If gravity is greater than resistance, then it means that the rain is doing an accelerated motion, if gravity is equal to the resistance, it is doing a uniform motion, and if the gravity is less than the resistance, it is doing a deceleration motion.

3.Same as the question above.

Don't be confused, the two-force balance here is to maintain the original state of motion, not to change the original state of motion.

If an object at rest is balanced by two forces, then it is at rest.

If an object in motion is balanced by two forces, it is in motion, and it is at a constant velocity.

Your additional question:

When you understand it this way, you think that the hand only gives the balance of two forces, but you have to think about it, when the hands exert force on each other, they also exert a frictional force. There's friction between your hand and the object, that's why it stops.

If the contact surface between your hand and the object is absolutely smooth, the object will still be moving at a uniform speed.

It's the same thing with a rope tying the ball, you straighten the string while also exerting an upward force on the ball.

You don't believe that you can pull a stationary object with a rope, but when you straighten the rope, does the object move upward?

1.Dual-force balance is a concept.

Definition: An object is said to be in equilibrium if it can remain at rest or in a uniform linear motion when it is subjected to two forces. (That is to say, at this time, the two forces are balanced, and the resultant force is 0).

2.There is a little contradiction in your question, a little boy pushes a box to move in a uniform linear motion, and of course the box will move (the net force of the object at rest and in a uniform linear motion is 0, refer to the definition).

3.The point of action is necessary in the middle, and we define that point as the center of gravity, which means that the force on the object is uniform. If you really don't understand it, just memorize it.

luck

We might as well use the way of counter-proof, if the net force is zero, the object cannot move in a straight line at a uniform speed, then it is obviously wrong to say that the force is the cause of the object's motion; And it is precisely because there is no other force or when the two forces are in balance that the object will remain at rest or move in a uniform linear motion, that is to say, the net force of zero will not necessarily make the box rest, but may also make the box move in a uniform linear motion.

In addition, if the net force is not zero, if the thrust is greater than the drag, an acceleration will be generated, and then the box will push faster and faster, breaking the uniform motion.

When the three forces acting on a rigid body are balanced with each other, the lines of action of the three forces are fixed on the same plane.

The rigid body is balanced under the action of three forces, in which the resultant force of any two forces is equal in magnitude and opposite to the third force, and the three forces must be in the same plane, and the resultant force is 0. So, when the three forces acting on the rigid body are balanced with each other, the lines of action of the three forces are fixed on the same plane.

False] When a rigid body is balanced by the action of three forces that are not parallel, the lines of action of the three forces must be coplanar and converge at one point, and this theorem is called hypertonic chaos as the intersection of three forces theorem.

Ganghe Youshu is in balance under the action of three forces, and these three forces must converge at one point.

a.That's right. b.Mistake.

The answer is: a

The three forces of the fixed pulley are balanced when they are parallel, but the three forces do not converge at one point.

A two-force equilibrium is when an object experiences two forces with zero net force, and these two forces are in equal reverse. According to Newton's second law, the acceleration of an object is zero;

The acceleration of the object is zero, and its motion or remains stationary; Or do a uniform linear motion.

Therefore, when the two forces are balanced, the object can move in a straight line at a uniform velocity.

1. First of all, we must correct one of your common sense mistakes: force is not the cause of the motion of the object, but the cause of changing the state of motion of the object. If an object is not subjected to a force (equivalent to force equilibrium), it will either be stationary or will always move in a uniform straight line.

Usually you see an object slipping on the ground for a while and then stop because the ground has friction on the object, and if there is no friction, the object will keep moving. Therefore, in the elevator, people move in a straight line at a uniform speed, which means that there is a force that cancels out the gravity of people, that is, the pulling force. Otherwise, if there is only gravity and no pull, the person will accelerate downward, as if falling from above.

The tensile force of the elevator is not a fixed value, at the beginning of the tensile force should be greater than the gravity, then the elevator can change from stationary to upward motion, and then the tensile force becomes smaller and becomes the same as gravity, then the elevator begins to do uniform motion (it can't be accelerated forever).

2. It's still 10n. You should remember that as long as the good motion of an object is a uniform linear motion, no matter what its speed is, then it is in equilibrium, and the pulling force must be equal to the frictional force.

3. Because at the beginning, the speed of you and the boat relative to the surface of the water is the same. That is, you and the boat are moving in a straight line at the same speed, and in the process of jumping up and falling, no other force acts on you, that is, without force, the motion of the object will not change. You're still moving with the boat as you jump on deck.

So it must have been in the same spot on the deck when it fell.

1) The law of inertia is based on an ideal environment, ideally there is no resistance, that is to say, there is no friction, there is no air friction, and the ground friction slows down the body, so it can move in a straight line at a uniform speed.

You ask whether an object needs to be subjected to force in order to move, and I think we should give you the answer in two aspects, first, the object itself is stationary and destroys, so that it needs a force to change its motion state, so it needs a force to have an instantaneous effect on it. But it's just a moment, in fact, the law of inertia just says that the motion of an object does not need to be maintained, that is, once the object is in motion, it does not need to continue to exert force on it.

Second, the object itself is in motion, and such an object does not need force to continue moving, because it can remain in motion under ideal conditions.

Do you understand? First of all, it is necessary to understand that the law of inertia is based on ideal conditions!

2) If you understand the first one I said separately, you can easily understand the second question you asked, there are two kinds of states of motion, motion and rest, a thing that is placed on the ground and does not move, the two forces are balanced (gravity and the earth's supporting force against it are balanced and balanced), and motion is the same but only in a straight line at a uniform speed.

It should be noted that there is no reality in true uniform linear motion, only in ideal cases.