The world of sound and the movement of forces High forces and movements.

1, B in the family hears the actor's voice first.

2. When the water level rises, the pitch gradually increases, and the loudness decreases.

3. It's a rope, not an earth or a bucket.

4. The selected references are the ship and the ground.

Let me explain, 1, A is in the field, 34m distance, the sound to A needs.

Obviously, B heard the voice first.

2. Fill the thermos flask with boiling water, the sound we hear is generated by the vibration of the air column in the thermos flask, as the water level rises, the air column becomes shorter, the tone gradually increases, and the frequency becomes larger, and the loudness decreases.

3. When lifting the rope, the hand is subjected to the action of a vertical downward force, and it is the rope that is in direct contact with the hand, not the earth or the bucket!!

The force on which the bucket is subjected by its own gravity is acted upon by the earth, the force exerted on the rope is acted upon by the bucket of the earth, and the force exerted on the hand is acted upon by the rope.

If you are carrying a bucket, then the force on your hand is the bucket

4. The scenery is full of flashes, and the mountains are just like walking to welcome:

Please note: there is a poet who takes a boat and looks out from afar! So you have to admit that the boat is moving opposite the shore!!

Also, you have to admit that the mountain is not moving against the shore!!

If you take the mountain as a reference, it is obvious that it is not moving, ** what is "looking at the mountain just like walking to welcome"?

This is what you see on the ship, that is, the ship as a reference!

Look carefully at the mountains and mountains not moving, it is a boat line.

As mentioned earlier, "If you take the mountain as a reference, it is obvious that it will not move itself", so the reference is the shore (ground)!!

It's so tiring to type

1.Because the air spreads slowly.

2.I don't know.

After the parachute is opened in motion, the air resistance is related to the falling speed of the person, and the greater the falling speed, the greater the air resistance.

Eventually the air resistance is equal to the force of gravity, so do the motion at a constant speed.

2. The object moves in a curvilinear motion.

You can write a 100,000 word essay to discuss the relationship between force and motion involving motion mechanics. Elastic mechanics, molecular mechanics.

Force has the effect of accelerating or decelerating the movement Specific situation Specific analysis.

1 None can't, because the original hot air balloon and the earth are in a state of motion (the earth rotates), when the hot air balloon lifts off, due to inertia, it still maintains the original state of motion (moving at the same speed as the earth), and is stationary relative to the ground, so the hot air balloon is still in place, so his idea cannot be realized.

2. What is the motion of the object when the force and motion of the object are not in the same direction? 1 When the parachute is not opened, the gravity is greater than the air resistance So do the acceleration exercise After the parachute is opened, the air resistance is related to the person falling.

In some cases, when there is no friction, the object will move in a straight line at a uniform speed, or at rest.

Can you be more detailed? f=ma, the force is equal to the mass multiplied by the acceleration. There is no direct correlation between force and speed. Alternatively, reference can be made to the momentum theorem.

Of course, it matters, if you exercise regularly, then your strength will gradually increase!

Wrong. For example, if an object is moving in a circular motion at a uniform velocity, the net force is not zero, and the velocity is constant.

The correct option is d

Because the interaction force is characterized by two forces of equal magnitude and opposite directions, acting on a straight line and acting on two objects respectively.

In addition, the nature of these two forces is the same. In this way, both forces are elastic forces.

d b was chosen because of the different nature of the force.

c is because the point of action of the force is not on the same object.

Let the initial kinetic energy e of the ball be thrown upwards, the maximum height h, and the air resistance f is a uniform deceleration motion when the ball is thrown upwards, and the kinetic energy at h 2 must be e 2 (which can be deduced from 2as=v 2).

According to the relationship of energy conversion, there is e - e 2 = mgh 2 + fh 2 It can be seen that the kinetic energy e 2 is greater than the gravitational potential energy mgh 2 at this time, and the kinetic energy can only be equal to the potential energy if it continues to rise for a certain distance.

So such a point is above H2 when it rises;

When falling to h 2, the kinetic energy is e'=mgh 2 - fh 2, which shows that the kinetic energy e' is less than the gravitational potential energy mgh 2, and the kinetic energy can be equal to the potential energy if it continues to fall for a certain distance.

So when falling, such a point is below H2.

There is a mantra

Up and down, the first up is the ascent process

The second is above the midpoint

The first one is the descent process

The second lower is below the midpoint.

It's more annoying to push... I'm lazy.

c The definition in the book says that force and acceleration are necessarily related.

There is no diagram to tell you the specific steps, and it should be able to be solved.

1. Set the angle between the thin rod and the ground r small ring weight m universal gravitational force g f1 = f2 = 5n2, and obtain f2 = m * g * sinr3 by uniform linear motion under the force of 5n, and obtain f1-f2 = m * 4 and m = 1kg under the force of uniform acceleration

5、sinr=1/2 r=60°

The questions are not difficult, and if you do more physics, your grades will improve.