Physics in the second year of junior high school I Physics in the second year of junior high schoo

1.Motion is absolute, which means that in fact everything is in motion, from the planet to the atoms and molecules in matter, all of which are in constant motion, and there is no real stationary object!

2.Motion is relative, meaning that the same object has different forms of motion due to the different frames of reference. For example, if you take a car as a reference, the tree is moving; With the earth as a reference, the tree is stationary (of course, the tree is actually moving, because the earth is rotating, so there is no contradiction with 1).

And you say that if you close your eyes, you don't know who is moving, but in fact this is an idealist philosophy. Natural science, on the other hand, is based on a materialist philosophical outlook. That is, the object is moving, and it doesn't stop because you close your eyes or don't think about it!

Motion is absolute, rest is relative, there is no absolute stillness; That is to say, an object can be stationary relative to another object, but there must be a situation where it is in motion relative to some other object, and an object is in motion relative to another object, and it may be in motion relative to other objects, that is, an object must be able to find one or more objects that are in relative motion with it, but it is not necessarily possible to find an object at rest with it.

If a person walks on it, then the person is in motion relative to the raft and the shore, and there is nothing stationary with it (other objects are not considered for the time being, and the specific situation is analyzed when considered).

The compressor sometimes works and sometimes rests during the day. It only consumes power and does work when it works, so according to p=w t, w=, there is no problem with this calculation, and t is less than, and far less than 24h, so the calculation of power p is small.

The true power should be calculated by dividing the W by the operating time of the compressor. Because the refrigeration effect of each refrigerator is not the same, it is not easy to calculate. You can use another formula for calculating the power of electricity, p=ui, (u is the voltage, i is the current, these two data can be found from the nameplate or description in the refrigerator) to calculate the power of the refrigerator.

Hope it works for you!

The refrigerator does not work 24 hours a day, there are intermittent ones, and it will stop working when the temperature is lower than the set temperature, and start working again when the temperature rises to the corresponding temperature.

If A's image is larger than B's, the image distance is larger, i.e., A's negative is farther away from the lens.

The relationship between the size of the image and the image distance, the larger the image distance, the larger the image.

As can be seen from the figure, b moves downward (the car has to drive on the right) and moves a pole position.

cDownward movement Movement of one pole position.

aUpward movement, movement 2 pole positions.

So the velocity a>b=c; If there's a speeding thing, it's an a.

Verify this: 60 2=30m s==30*

A car is speeding. B**The negative is far away from the lens.

From the analysis of **, B and C always maintain the distance between 2 street lights, and car A exceeds the distance from 1 street lamp to 2 street lights from car B. Therefore, the speed of car A is at least (the speed of car B +45m s) is significantly more than 80km h; So the first blank fills in a.

The magnification of image A is larger than that of image B. Because the cameras are all real images, the magnification is v u, v is the image distance, and u is the object distance, so the image distance of the first is large, and the negative is far away from the lens, so the second blank fills the nails.

First, the answer.

1. Electrical appliances.

2. Power supply, switch, wire, electrical appliances; Power supply, electrical appliances, wires, switches3, circuit diagrams.

4. Energy; Chemistry, Electricity; Electricity, chemistry.

5. Path, open circuit (or open circuit), short circuit.

6. There is a power supply and the circuit is the path.

2. 1. Current, heat.

2. (1) strings; (2) positive and negative; (3) Measuring range; (4) Power supply, current, ammeter 3, test touch, maximum, touch, smaller.

4. Equal. 5, negative binding post.

6. The current is equal everywhere, and the trunk current is equal to the sum of the currents of each branch.

Surely it is!!

1.with electrical appliances.

2.Power supplies, switches, wires, electrical appliances.

3.Circuit diagram.

4.Chemical energy within electricity and electricity.

5.Path: Short circuit or open circuit Short circuit.

6.One: There is an electric current passing through the two: There is a useful electrical appliance.

II, 1The current heat.

2.(1) Skewers.

3) Maximum range.

4) Power current power supply.

3.Try to touch the large access small.

4.Equal. 5.-6.The currents are equal everywhere The power supply (trunk) current is equal to the sum of the currents of each branch.

1 （1) 24w

2）240r/3000r=

3)w=t=3min=3*60s=180s

p=w\t=160w

4) U=IR=Euro=240V

2-column equation R1(6-2U1) = (6-U1)R22R1(3-U1) = (6-U1)R2

2r1/r2=(6-u1)/(3-u1)

r1/r2=3-u1/2/3-u1

r1/r2=1/u1/2

r1/r2=2/u1

Because p1 = p2

So r1=r2

So the total resistance of the rheostat is at least 2 ohms.

1)24w2)240/3000=

3) (411-240 3*5) 3000*4) old electric water heater resistance = 220 2 44-600 = 500 ohms.

u 2 = pr u = open root 12000

Formula: :p=U2R

The spot will move to the left. Please see**.

It's moving to the right, you can draw a straight line above the water surface to simulate the water surface rising, and then you draw the method, the angle of incidence is already there, and then you draw the reflection angle, and you will find that the reflection angle of the water rises and moves to the right.

Move to the left.

You can draw a normal.

The angle of incidence and the angle of reflection are equal.

Left, the liquid level rises and the normal moves to the left, the angle of incidence and reflection remain unchanged, and the reflected spot moves to the left.

1.Echolocation, or echo shaping.

2.Because the glass resonates with the horn. In other words, the horn transmitted his vibrations through the air to the glass, and the glass vibrated so that it shattered.

3.Because the frequency of the flying bee's flight vibration is within the range of the human ear's hearing frequency, that is, within 20-20000Hz, it can be heard; And when the butterfly flies, the frequency of flapping its wings is outside this frequency, so it cannot be heard.

4.The appearance of the snow is uneven, and the sound is gradually weakened as it travels over the surface of the snow, and if it is far enough away, the sound disappears completely. That's why the walls of the General Assembly Hall are uneven, not just for aesthetics, but also to dampen the echo.

1.Dolphins are judged by the timbre of the vocal body.

2.Because sound transmits power.

3.Because we distinguish objects by the timbre of sound.

4.After a heavy snowfall, there is a lot of snow on the ground, so it blocks the transmission of sound, so the sound becomes quieter.

I don't know if it's right, you can refer to it

Upstairs is Pig 1: Dolphin via echolocation.

2: Sound can transmit energy.

3: The vibration frequency of bee wings is 20 20000hz, we can hear the butterfly vibration at 20hz, which is inaudible.

4: Snowflakes are loose and porous and can absorb sound.

1. The moon is so far away from the earth that the distance between it and the moon is felt to be constant.

Second, it is also because the moon is very far away from the earth, so even if people are moving, the perspective of people looking at the moon on the earth is the same.

From the above two points, it can be concluded that people's feeling is that people and the moon are relatively static. So teasing: the cherry seller runs, and the moon follows.

The moon is so far away from the earth that people feel that the distance between them and the moon is constant, so when people run on the moon, they follow it.