There are three SG devices, and three devices are placed sequentially along the j axis

(copy1) will be installed.

A and device B experiments were compared and found that there was a unique variable - moisture The seeds in device A do not germinate, and the seeds in device B germinate, and the seeds can be obtained to germinate a certain amount of water

2) This experiment can only form a set of controls, that is, the control of device A and device B Therefore, this experiment can not prove the effect of temperature on seed germination, and no control experiments with different temperatures are designed

3) If it is proved that "sunlight is not necessary for seed germination", in addition to the use of device B, it is necessary to add a control group, please design this control group: add a device identical to B, and put an opaque box on the outer cover of the device

4) Comparing the experimental results of devices B and C, we found that there are two variables between B and C - air and light (C shading), which cannot be contrasted and therefore cannot be concluded that air is needed for seed germination

So the answer is: (1) moisture.

2) No, because control experiments with different temperatures were not designed.

3) Add a device identical to B, and put a light-opaque box on the outer cover of the device (to shade the device).

4) No, because there are two different conditions (air and sunlight) between b and c

(1) There are 2 groups of control tests in this experiment.

Source test, such as the device.

A and device B experiments are compared and found that there is a unique variable - moisture In device A, the seeds do not germinate, and device B seeds germinate, and the seeds need a certain amount of water to germinate The other group is B and C, and the variable is air

2) The experiment can only form a set of controls, that is, the control of device A and device B In order to design a control experiment of "sunlight is not necessary for seed germination", there must be a unique variable - light, so in addition to using device B, add a device identical to B, and cover the device with an opaque box (to shade the device).

Therefore, the answers are: (1) 2 Seed germination requires a certain amount of water c and b (2) experimental variables; Add a device identical to B, and put a light-opaque box on the outer cover of the device (to shade the device).

The speed of light is less than 3 times 10 to the 8th power.

In 1849, Fisso (the first to determine the speed of light on the ground by experimental methods) using the rotary gear method, and the propagation speed of light and its measurement are closely related to many fundamental problems in physics. The speed of light c is a fundamental physical constant. The measurement of the speed of light is a very important topic in physics.

Looking back at the history of the measurement of the speed of light, the first thing that comes to mind is Galileo Galilei, the founder of modern physics, who first proposed the concept of the speed of light as a finite and tried to measure the speed of light. As early as 1676, the astronomer Romai (calculated the value of the speed of light from observations of Jupiter's moons. In 1849, Fisso (the first to experimentally determine the speed of light on the ground using the rotating gear method.

In 1862 Foucault (measured the speed of light in the air by the rotating mirror method. Special mention should be made of Michelson, who made several systematic measurements of the speed of light, providing valuable information for gaining insight into the nature of light and establishing new physical principles.

We all know that when an object reaches the speed of light, the ruler shortening effect and time dilation will occur, which is due to the fact that the speed of the object is approaching c from 0, and the change of space is from three dimensions to two dimensions, and the object must shorten the one dimension in the direction of motion; When the velocity is c (or greater than c), the space changes into two dimensions, and the one dimension of the object in the direction of motion is shortened to 0, which is also two-dimensional. Since this shortened dimension is inseparable from time, time also expands to infinity at the same time, and there is no time.

The ruler shortness effect refers to the length that a ruler with energy of 1 m on Earth can only measure in matter close to the speed of light or reaching and exceeding the speed of light.

Time dilation is when people who spend 1 year on Earth are much older than people who are in matter close to the speed of light or arriving and exceeding the speed of light.

But herein lies the problem:

Light is moving at the speed of light, and the light must have a ruler shortening effect, so the light travels m which is equivalent to 1m in realitySo I think the real speed of light is less than 3 times 10 times 8 power.

Light is moving at the speed of light, and light must undergo time dilation, so a few seconds of light is equivalent to one second in reality, so I think the real speed of light is less than 3 times 10 to the 8th power.

Combined, the speed of light above is less than 3 times 10 times 8 power, and much smaller.

P.S. The matter thrown out by the superplanet** moves many times or even hundreds of times the speed of light.

It is recommended that the landlord go to the library to borrow Hawking's "A Brief History of Time", which has a very detailed and authoritative answer to this related question.

(1) a, the end of the chute remains horizontal, so that the ball has a horizontal initial velocity, so a is correct b, c, each time must be dropped from the same height by stationary, so that the ball leaves with the same velocity, so bc is correct

d. When the ball is moving, it can not be in contact with the white paper (or coordinate paper) on the wooden board to avoid changing the movement trajectory due to friction, so D is correct

e. In order to make the traced trajectory better reflect the real motion, the recorded points should be appropriately more, and connected with smooth curves, so E is wrong

Selection: ABCD

2) According to the meaning of the title: hab

100-90=10cm=，hbc

90cm-70cm=20cm=

In the vertical direction: h=gt2, horizontally: x=v0t, where h=hbc

hac=,x=l=20cm=, substituting data to solve: t=,v0=

So the answer is: (1) ABCD; （2）2m/s．