The question of the first chapter of physics in the second year of junior high school, as long as th

1.The eardrum of the human ear is a thin, elastic membrane like the membrane of the drum, and when sound waves pass through the ear canal to the eardrum, the eardrum vibrates and transmits this (vibration) to the cochlea

2.Since the distance from the sound source to the human ear is different, the difference in the time, intensity, and other characteristics (differences) of the sound to the human ear is an important basis for judging the sound source (location), which is called the binaural effect

3.Musical instruments such as the erhu, violin, and guitar all have a sound box, and their role is to create resonance, and through the resonance of the sound box and the internal air, the sound of the vibration of the strings is amplified.

In order to play the role of the sound box, you can pluck the strings without the sound box, and then pluck the strings with the sound box 1, and compare the difference between the loudness of the two, the latter has a louder voice, indicating that the sound box has the effect of amplifying the sound.

1. Liquid: water, juice. It has fluidity and does not have a certain volume.

Solid: wood, books. There is a certain volume.

Gaseous state: air, water vapor. It has fluidity and does not have a certain volume. 2. First of all, molecules are made of atoms, and the physical properties are different because of the different ways in which their atoms are arranged! Hope it helps you ( o ) !

First of all, molecules are made up of atoms, and the physical properties are different because of their different atomic arrangements, and the microscopic explanation 、、、

Liquids: water, oil, etc. are free-flowing, solids: ice, iron, glass, etc. have a fixed form.

Gas: oxygen, nitrogen, some rare gases, etc. Note: Smoke is not a gas, it is a solid small particle without a certain shape.

The order in which the atoms are arranged and the structure of space are different...

Liquids such as water have volume and no fixed shape; Gases such as air have neither a fixed volume nor a fixed shape; Solids such as ice cubes have both a fixed volume and a fixed shape, and their physical properties differ due to the different ways in which their molecules are arranged and the forces that act between them.

The first chapter of this ninth grade has a very detailed explanation of the value that was found to give me.

v0=90km/h=25m/s

The distance in the reaction time is s1 = v0 * t1 = 25 *

Braking distance s2 = 60s

Average velocity v=(s1+s2) (t1+t2)=(15+60) (

First of all, v=s t is required, and then the total time and total distance are required.

s total = 90 km h*

t, total = v=s t=210m, the final answer is calculated by yourself].

There are two methods, one is to find the pressure of the tank according to its weight, and then compare it with the pressure that the ice can bear, if it is greater than the pressure that the ice can bear, it will not pass. One is to calculate how many tanks can pass through based on the pressure that the ice can bear, and compared to the mass of the tank, it cannot pass if it is smaller than the mass of the tank. Let's use the first one:

p=f s=25*1000*<, can pass.

The second type: g=f=p*s=>25000kgTherefore, it can still be passed.

3000r min is equivalent to 3000 revolutions of the flywheel in one minute, with an average of 50r s, which is 50 revolutions in one second.

For an internal combustion engine, it uses four strokes to complete one cycle, in which it does only one work, that is, its work stroke, and to complete one cycle, the flywheel has to make two turns.

It is equivalent to saying that if the flywheel rotates twice, it can complete one work, and now, in one second, if the flywheel turns 50 times, it will complete 25 cycles, that is, it has done 25 work.

The title says that it does 1000J of work once, so in one second, 25 times of work, this internal combustion engine does 25000J of work, and these works are completed in one second.

According to the formula of power: p=w t, it can be calculated that p=25000w, which is 25kw

3000r/min÷2=1500

There are 2 duty cycles per revolution).

1500 60 seconds = 25 times (1 minute = 60 seconds) one power stroke is 1000J

So the power is 25 1000J = 25000W

of the fourth power kw

The process is very detailed