A physics problem in the second year of junior high school! Ace enter!

Decline. The principle of this thermometer is the thermal expansion and contraction of gas, and under the same conditions, under normal circumstances, the expansion degree of gas is the largest, which is greater than the expansion degree of liquid, so if the temperature rises, the gas will be liquid"Press"goes down, so the liquid column falls. (Definitely yes, 08-09 Yangzhou City eighth grade first semester final research paper penultimate question 2).

As the temperature rises, the liquid level in the tube drops.

Today's thermometers are made according to the thermal expansion and contraction properties of liquids, while Galileo gas thermometers are made according to the thermal expansion and contraction of gases, when the air temperature rises, the gas expands, and the liquid column falls. (Sure, our teacher told you).

Descent (I did this).

Principle: thermal expansion and cold contraction.

will go down. Because the Galileo gas thermometer is made according to the principle of thermal expansion and contraction of air. When the temperature rises, the thermometer air will expand hotly and the liquid will naturally fall. The higher the temperature, the lower the length of the liquid column. If the temperature is low, the opposite is true.

His thermometer was the opposite of the current liquid thermometer and was more troublesome, so it was not widely used.

Decline. As the temperature rises, the air in the spherical flask expands, and the air pressure inside the flask increases, pressing the water downward.

Let's go up. Does this pressure have anything to do with it?

f=ps .When the temperature rises, the pressure increases, the area remains the same, and the pressure increases.

The air presses the liquid upwards.

The liquid column will drop the handlebar

Thermal expansion and cold contraction

I guess.

As the temperature rises, the liquid level in the tube drops.

When the temperature increases, the gas expands, and the gas pressure increases, and the pressure generated by the difference between the height of the water in the tube and the height of the water surface = atmospheric pressure.

The atmospheric pressure is considered to be constant, and the pressure of the gas increases, and the pressure of the water in the tube decreases for a long time, and its height decreases, and the level of the tube decreases.

Before the detonation, the switch S is closed, at this time the circuit diagram can be equivalent to the initiator and the section of wire at the switch in parallel, then the detonator is short-circuited, there will be current through point B, not through point A, so, at this time, there is no current through the detonator. If you want to detonate, you need to disconnect the switch S, then the detonator will not be short-circuited, and there will be a current through point A. Therefore, whether the initiator will be ** depends on whether there is an electric current passing through point A.

Well, the bomb disposal specialist should cut the wire at A.

In the figure, the initiator is short-circuited by the switch and the B circuit, when the detonation time is set, the timing switch S will be automatically disconnected which means that it will no longer be short-circuited, so that the detonator has a current and can work.

The current starts from the positive pole of the power supply, passes through the bulb, A, and then divides into two paths, one through the initiator, the other through the switch and B, and finally converges to the negative pole of the power supply. Then in the two roads, the resistance of the switch and B is very small (in junior high school, I think there is no resistance), and the current is very large; The other one has resistance, and the current is very small, and it can be considered that there is no [commonly known as the detonator being short-circuited].

Before dismantling, the switch is closed, and the initiator is short-circuited by the switch and the wire at point B, so no current flows.

If the switch is disconnected, the detonator and the power supply will be connected in series, and there will be a current flowing through it, and the bomb will **.

The purpose of defusing the bomb was to hope that no current would flow through the detonator.

After cutting A, the initiator only forms a circuit with the switch and point B, and the branch of the power supply is disconnected, so there is no power supply in the circuit of the initiator, and there is no current.

It must be cut point A, and if point B is cut off, it means that the current will flow to the initiator. As shown in the figure, because the resistance between the battery positive --- switch S --- point B--- the negative electrode of the battery is smaller than that between the positive electrode of the battery --- the initiator --- the negative electrode of the battery, according to the characteristics of the current, the smaller the resistance, the greater the circulation. Therefore, when the switch S is disconnected, the current will flow to the initiator, if the A point is cut, there is no loop between the positive electrode of the battery--- the initiator --- the negative electrode of the battery, and there will be no current.

Now you see this circuit, there is no current through the detonator, because there is a wire that short-circuits the detonator, if you cut B, then there is a current flowing through, the detonator will heat up, and then it will **.

As can be seen from the diagram given in the title, the switch S and the initiator are connected in parallel. When the switch S is closed, the initiator is short-circuited, i.e., no current passes: when S is disconnected, the initiator has a current, that is, the initiator is turned on, which will trigger **.

Therefore, the key to this problem is to let the initiator have no current to pass, that is, the circuit diagram is not passable, that is, cut off point A in the question.

Before detonation, the initiator is short-circuited and the current starts from the positive pole of the power supply and passes through wire B, switch S, wire A, and the small bulb back to the negative pole of the power supply.

Cut-off s the current from the positive pole of the power supply through the detonator, and the wire A small bulb returns to the negative pole of the mains.

When A is cut off, the circuit becomes an open circuit, and there is no current passing through the circuit.

Before dismantling, the circuit path is s a power supply b does not pass through the initiator, so the initiator has no current.

After a shear, one pole of the power supply is disconnected and there will be no path so there is no current.

Simply think about it, if there is an electric current through the detonator, wouldn't it be ** haha.

Fill in a, b is the same as s disconnecting, no difference.

There is also no current before the detonator is dismantled, because the S is closed, a short circuit is formed, and the current will not pass through the detonator.

Cut off A, disconnect the circuit, the initiator does not detonate, S is closed before detonation, the wire at B shorts the initiator, and the current flows back to the negative pole of the power supply from the wire B. There is no current in the initiator. If there is an electric current, it will explode.

In the beginning, the detonator was short-circuited, so there would be no current. If there is to be an electric current flowing through, it will be **.

When the switch is closed, the detonator is short-circuited, so no current is passing through!

The initiator is short-circuited before S is disconnected, and the current starts from the positive pole of the power supply and returns to the negative pole through the bulb, A, S, and B, and there is no current on the initiator.

The upper 4 fixed pulleys have a force arm ratio of 1:1 so it does not save effort, and the lower 2 force arm ratios are 2:1, so the arithmetic formula is 50 4=

As shown in the figure, the wire where 1 and B are located can be regarded as being connected in parallel with the initiator; 2. In parallel circuits, the voltage is equal, and the current is inversely proportional to the resistance. Third, the initiator resistance is large, the wire resistance is very small, and the two can be regarded as infinity compared with the initiator resistance, so there is almost no current passing through it, and the current is almost divided by the circuit where B is located.

PS: In fact, the initiator should also have a weak current, but this current is too weak, too small to start the detonator, in order to avoid confusion, this negligible current is called "no current".

Dialectically, there is no absolute thing in physics, it is like saying that rubber does not conduct electricity, strictly speaking, it also has a certain conductivity, but the resistance is very large, and the conductivity is so bad that it is negligible!

I think C should be chosen

Usually the formula for solving the leverage problem is f1l1=f2l2 at this time, f1, f2, is equivalent to the mass of two ants, l1, l2 is equivalent to the distance, according to the formula s=vt, the time is the same, so the distance depends on their speed, look at the formula f1l1 again, the problem is the mass and speed of the ants.

The mass of ant A can be greater than the mass of b, but the velocity of ant A must be less than the velocity of b.

Conversely: if the quality of Ant A... The same is true but their product must be the same for their final effect to be the same, i.e., always maintain a balanced qq connection: 391467819

Choose C, the leverage problem is only, F1L1=F2L2, F1=M1G, F2=M2G, L1=V1T, L2=V2T, sort it out: M1V1=M2V2

c. Power multiplied by power arm = resistance by resistance arm.

Choose C, because of balance, so m*l=m*l, and because of the constant velocity, v is proportional to l, so the product of the mass of the two ants and the crawling speed must be equal.

The c process is not easy to explain, read the question slowly.

Select c with the condition of conservation of momentum.

In one system.

The system maintains its original state of motion.

Then the positive and negative momentum of this system are equal.

Momentum p=mv

The constant velocity in the question means that the velocity of the ants is constant, but it does not mean that the velocity of the two ants is the same.

Pick C because it keeps the balance.

C choose C answer in the name of the physics teacher!

How can this question be the question of the second year of junior high school, it should be the second year of high school!

Straw equilibrium means that the resultant force on the straw is zero, and the two ants exert a frictional force on the straw in the horizontal direction that is opposite to their direction of movement but equal in magnitude. We can also say that the sum of the impulses of these two frictional forces is zero. According to the relationship between the action force and the reaction force, the wheat straw also has frictional force on the ants, and of course there is also a frictional impulse, and the impulse for each ant is equal in magnitude and opposite in direction.

The impulse of the force is equal to the change in momentum, and momentum happens to be the product of mass and velocity...

The time is all the same ...

So choose c my God, the current junior high school questions are too scary...

Choose C. Moment balance! It's just the distance of the ant from the center multiplied by the same mass. But the time is the same, so the speed of the two ants multiplied by the mass is the same!

c, to ensure that the torque on both sides is equal!

It's like when you sing, it's true and falsetto. It is the pitch of the pitch. Broken porcelain is equivalent to you switching from real voice to falsetto singing、

And the male singing and the female singing are the timbre. Different objects have different timbres.

Timbre: Different substances emit a fixed sound (just like you can tell who it is when a friend around you speaks, this is timbre).

Tone: Focus on the "key". Objects are all vibrating and emitting different frequencies (i.e., the speed of vibration, which we generally do not feel), which is related to the internal density and structure of matter (you will learn this later, so let's note it for now).

First of all, there is only one substance in your topic: ceramics (the timbre does not meet the requirements), and secondly, the question is to judge whether the ceramics are good or not according to the damage, and "breakage" is the key, because the density is different, the vibration is different, and therefore the tone is different.

You can follow the above analysis method for such a topic, but you still need to distinguish the respective definitions first, and then use your own understanding to elaborate.

Timbre is a property specific to matter, and the timbre of each object is different, e.g. male and female.

And the pitch is just the frequency of the sound, such as male and female voices can sing high notes, singing 123456 notes.

That's the difference between them.

1. All set the maximum value of sliding rheostat r to r, and the power supply voltage e

then (e-4) 4=2r1 r

e-4-2)/6=r1/r

Divide by the two formulas to give e=12v

So r1=9 r=9

So AB is wrong.

The ratio of the electrical power consumed by C to R1 is (E-4) 2:(E-6) 2=16:9d.

It should be a kilogram of Celsius with a high density of water.

In fact, the question is to ask you which is the denser ice or water?

The answer is that water is dense, and the fact that ice can float on water illustrates this.

The density of water ice is lower than that of water when the mass is the same.

The density of water is high! It has nothing to do with quality

For example, who is more dense than a ton of cotton or a gram of iron?

For an object to move in a straight line at a uniform velocity, then the traction force is equal to the frictional force.

For an object to accelerate, the traction force must be greater than the frictional force.

Regardless of the speed, as long as the speed is moving in a straight line at a constant speed, the traction force is always equal to the friction force.

1. The object needs to receive an external force to change the state of motion.

Two: non-smooth surface contact friction will produce friction.

Three: Uniform linear motion is that the traction force is equal to the frictional force between the ground and the wheels.

Hope it helps.

1.Car start-up is an accelerated process.

2.The starting power of the car is greater than the resistance.

3.The force is balanced when the car moves in a straight line at a constant speed.

4.Rolling friction is much less than sliding friction.

That's all I can think of, and if some of them don't fit well, I really can't think of anything closer to the example!

First of all, the title is wrong. It should be elongated centimeters.

Because the four are connected in parallel, the pulling force is evenly shared.

There is also a misunderstanding that both hands are pulled with 2 Newtons, and the elongation of the spring is only the effect of 2 Newton force. Niu Sanlu is slippery.

It's simple. Each stretch of the rice to the point of the mountain is a Newton's force, so it is equal to 2

Because there are four springs, each elongated to the centimeter requires a Newton's force, so it is equal to 2

There are four springs, and when you pull one you stretch to centimeters, and one one uses Newton's force, so it is equal to 2n