In the first year of junior high science, help, there is a first year science question, so everyone

The temperature does not change.

bOrganic plastics absorb heat when melting.

The melting point of the object is fixed, but the heat required to melt (energy conservation) is not right upstairs so c

Hypo during melting (c).

a Endothermic, increased temperature.

b Exothermic, the temperature is reduced.

The temperature does not change.

d No endothermic nor exothermic, the temperature remains unchanged.

The following statement is correct (ab).

aDiamond does not turn into liquids.

bOrganic plastics absorb heat when melting.

c At standard atmospheric pressure, the melting point of ice is the same as that of hypo d Rosin does not melt.

Quartz is a crystal.

Hypo during melting (a, c).

a Endothermic, increased temperature.

b Exothermic, the temperature is reduced.

cendothermic temperature does not change.

d No endothermic nor exothermic, the temperature remains unchanged.

The following statement is correct (ab).

aDiamond does not turn into liquids.

bOrganic plastics absorb heat when melting.

c At standard atmospheric pressure, the melting point of ice is the same as that of hypo d Rosin does not melt.

Hypo Quartz.

It's crystals.

Hypotherm is a crystal, so it neither absorbs nor exothermic during the melting process, and the temperature is kept at the melting point, so D is chosen

Any substance will have three forms of solid-liquid gas, while organic plastics do not have a fixed melting point, so they will continue to absorb heat during the melting process

cendothermic temperature does not change.

Because it is "melting", it continues to absorb heat while the temperature remains the same. If memory serves, it should be 48. ）

aDiamond does not turn into liquids.

Because diamond is carbon elemental, there is no liquid state. ）

Quartz is a crystal.

Right angle tripod, known ab = 3 m, bc = 4 m, it is known that ac=5 m.

The runner runs desperately along the ABC route at an average speed of M s, and the time it takes to reach point C is (3+4) seconds.

At the same time, if the cat catches the cat and chooses the AC route to point C, the speed of the cat is 5 2=.

So the average speed of running mice is large.

This question shows that efficiency is king.

1) The average speed of the running mouse is large, because the distance of catching the cat is 5m, and the distance of the running mouse is 7m, the time of the two is equal, and when the time is equal by the formula v=s t, the average speed is proportional to the distance, so the average speed of the running mouse is large.

2）t=(3+4)/ v=5/2=

1. Choose all A Thermal expansion and cold contraction Black is easier to absorb sunlight heat White is easy to reflect So the temperature of A is higher than that of B According to the principle of thermal expansion and cold contraction, the air expansion volume in A is a little larger, so choose A

Answers: A, L1>L2

Reason: Black is heat-absorbing and heats up faster than white.

Give it a good review!

Choose A. It is impossible to choose D! Black has strong endothermy, and the liquid column rises quickly in the same time.

a、l1>l2

Black absorbs all colors and heats up quickly.

1.Fan fans do not bring the temperature down.

2.Increases the velocity of the surface air flow of sweat on the body, speeding up the evaporation of sweat. So I feel cool.

3.Take two identical thermometers, smear a little water on the glass bubble of one of them, and do nothing at all. Then put the two thermometers together and fan the air with a fan.

Phenomenon: It was found that the thermometer with water was much lower than the thermometer without water. Conclusion:

The reason why I feel cool when I fan my body is (put 2.)Just write it down. I'm in junior high school, for sure.

Fan fans do not bring down the temperature.

Accelerate the flow of air on the surface of the liquid, and accelerate evaporation and endothermy.

Wrap gauze soaked in water around the thermometer, fan the air against the thermometer, and observe the thermometer's display.

[Fan fan can not change body temperature] [air flow accelerates the evaporation of body water,] Use two thermometers, one dipped in water and one untreated, use a fan fan].

1. Fan fan can not make the temperature lower.

2. With a fan, the flow rate of the wind becomes larger, the evaporation accelerates, and the body feels cool because of the evaporation and heat absorption.

3. Fan against the water fan, so that the flow rate becomes larger, the evaporation accelerates, and because the evaporation absorbs heat, so the thermometer in the air will drop at this time.

Xiao Nian's idea that the temperature was lowered by a fan was wrong.

Air convection accelerates the dissipation of heat from the body.

Two cups of boiling water, one with a fan and the other to rest. After a while, the temperature of the cup dropped quickly, because it lost heat quickly.

1. The name of the experiment: the sensitivity to the taste of the tongue.

Problem to be studied: The sensitivity of the four parts of the tongue (posterior side of the tongue - tip of the tongue - base of the tongue - anterior side of the tongue) to the four basic tracts of "sour, sweet, bitter and salty".

Experimental preparation (experimental equipment and medicines): a little vinegar, salt solution, strong coffee liquid, sugar solution, four chopsticks, water.

Pre-assumption: postlingual is most sensitive to acids; The base of the tongue is most sensitive to bitterness; The tip of the tongue is most sensitive to sweetness; The anterior lingual side is most sensitive to saltiness. (Hypothesis is casual hypothesis.)

**(Experimental) protocol design: Use chopsticks to dip different flavored solutions, and each solution is in contact with four parts of the tongue.

**(Experimental) steps and phenomena: 1. Use chopsticks dipped in white sugar solution to contact the four parts separately, and feel which part is more sensitive. The phenomenon is that the xx part is more sensitive.

2. Rinse your mouth with water. 3. Reuse ......(Repeat......Well, you understand? I won't hit them one by one, +

**(Experimental) Results: The posterior lingual side is most sensitive to acids; The base of the tongue is most sensitive to bitterness; The tip of the tongue is most sensitive to sweetness; The anterior lingual side is most sensitive to saltiness.

This experiment has taught me how to use the control variable method, and I will definitely pay attention to this method. In the next step, I plan to use the control variable method as well. I have learned that scientific research should not be done by listening to and believing in partiality, but by doing it yourself.

Date and signature of experiment: ......Do it yourself......I'm sure you ......Hey hey 0 ).

2. Scientific small production: remove one end of a waste can (such as Lulu beverage can) with one end of the lid, and knock the other end with a round hammer. Roll up two No. 1 batteries with thick corrugated cardboard and put them into the tank with the positive electrode facing up and the negative electrode facing down.

Find a suitable plastic lid (such as a magic big roll lid that can be fastened to Lulu cans) and dig a small circular hole in the lid** in such a size that the bulb is plugged in tightly. Insert the base of the bulb into the small hole. Take a piece of wire hunt and peel off the wire skin at both ends, wrap one end around the lamp base, and pierce a small hole through the side of the plastic cover with the other end.

Place the plastic lid over the can. Check that the bulb and battery are in close contact. At this point, the disposable flashlight is ready.

When using, use your thumb to press the wire threaded from the side wall on the weld that is not painted from the can, the flashlight will glow, and the thumb will jump off the wire, and the flashlight will go out, which is very convenient to use.

The first tongue root and the second one are bitter, and the back one is very troublesome, I'm lazy, I'm sorry.

(1) There are (5) food chains in this food web, which belong to the producers (grass) and to the primary consumers (herbivorous birds and insects).

2) Assuming that the energy fixed by the grass is constant, the owl gets the food chain with the most energy (herbivore bird owl).

26. Due to the discharge of a large amount of sewage into a lake, the water quality has deteriorated, resulting in the death of fish and other aquatic organisms, and the destruction of aquatic biodiversity. Please analyze and answer.

1) During the experiment, it is necessary to observe the main content of the record (the number of frog eggs successfully hatched in each ecological bottle).

2) The reason why they chose the number of fertilized eggs as 100 instead of 5 was (to avoid the chance of the experiment) [do not write to make the results of the experiment more accurate, it should be that the average value is not written in this question, but it can be added later to make the experimental results more general].

3) The role of group A ecological bottle is (control) [the role can be written directly to the control].

Proficient in mathematics, physics and chemistry to answer for you.

o(oThank you.)

25 (1) 5 food chains, from low-level predators to high-level predators, one by one, number (2) grass-insect-spider-toad-toad-snake-owl The longest is often the one that obtains the most energy26 (1) The number of frog eggs hatched (hatching), the basic knowledge of the controlled trial (2) Too few will produce a greater chance of chance (5 will have chance), ibid., examine the basic knowledge.

3) Form a comparison (make a comparison), the same as above, and examine the basic knowledge.

(1) The producer is grass, and the primary consumers are herbivore birds and insects (2) It is not very clear.

1) The number of frog eggs hatched in each eco-bottle.

2) Prevent chance and make the experimental results more accurate.

3) Set up a control group.

I'm 100% sure that's all I have, so please set it as a satisfactory answer for my sincerity.

5 Grass belongs to the producer Belongs to the primary consumer (except for the owl) (2) Assuming that the energy fixed by the grass is constant, the owl receives the most energy from the food chain (the lowest one).

Environmental water quality on the number of frog fertilized eggs hatched.

2) Improve the reliability of the experiment (the meaning is close to the control).

(1) 5 Herbivorous birds and insects, the word is not clear (2) Herbivorous insects owls.

26.(1) The number and time of hatching frog eggs.

2) Take 100 capsules to be more representative and exclude accidental interference (3) as a control.

Classmate: I can't see it.