7th Grade Science Questions Several 7th grade science questions

Choose BA to reduce medications. Because what you have to weigh is that this is your task and cannot be changed.

c Add weights to the right disk. If only the deviation but not that small weight.

c Adjust the balance nut. The balance nut is adjusted before the object is weighed. If it's 1 gram off and the pointer is off, adjust the balance nut so that the pointer points to the middle point, but you don't weigh the exact mass of the object, right?

To sum up, choose B.

Choose B left object right yard, left deviation means that the weight is not enough, but you can't add another 1 gram of weight, because it will be overweight.

And the weight is weighed with a decimal point, so the code should be moved to the place.

It must be a because the weighing is the drug, the weight and the code can not be changed, if the weight or the code is changed, the weighing of the drug is inaccurate.

Since the left plate is placed with a weighing object, the number of drugs should be reduced.

A first needs to look at the title, the topic is not known is how much the drug is added, not how much the drug is.

Therefore, to weigh the drug, you can first put a weight gram on the right plate, and then add the drug to the left plate until the balance is balanced.

Be sure to choose B left deviation means that the right disk is light, and the right disk should be aggravated.

But you can't add more weights, because you will definitely be overweight.

Therefore, the game code should be moved.

I'm good at physics.

d...Anyway. The pointer always stops in the middle. So the balance nut should be tightened to the right.

Pick A, believe me, I've been a science class representative for 3 years

b or c because a is definitely not right.

d is the work at the beginning.

1 is 24 meters 3

Pacific 4 is.

As long as it is a cell, it is already a living thing.

5 mosaics growing.

Photosynthesis. 6 capillaries.

7. Mainly the triceps muscle is contracted, and the biceps is relaxed.

8 The green grass is alive, and the energy released by their respiration is not only used for life activities, but also partly transformed into the fruit of maturity.

Let the time be x seconds, and the equation can be 10x+340x=455*2;Solution: x = seconds).

The car is from the cliff: 455-10* meters).

Neither A nor B can boil.

After the water in the container boils, the temperature reaches 100 and does not change, at this time A can reach the boiling point, but because it is the same temperature as the container, it cannot continue to absorb heat, so it cannot boil; On the other hand, because B is inverted, the air pressure in the cup becomes high, and the boiling point rises, and even the boiling point cannot be reached, let alone boiling.

If A does not touch the container, then A does not boil, while B touches the container and can absorb heat on demand, so it will boil.

Relative speed question, the first question, a day and night hand and the minute hand go 2 and 24 times respectively, then the number of coincidences is 24-2 = 22, after 9 o'clock in the morning, set a circle distance of 60, the speed of the clock is 5 per hour, the speed of the minute is 60, then the distance at the beginning is 9 * 5 = 45, the relative speed is 60-5 = 55, then the time = 45 55 multiplied by 3600 to convert to seconds.

Correct answer: BWhen there is water, see that the size of the sky is greater than s. It mainly examines the linear propagation of light and the reflection of light. The size of the sky seen with or without water is greater than s, and the deeper the water, the larger the area of the sky seen.

1. The race distance is the same, and the length of time is compared, so as to compare the speed of the time, that is, the speed of the long time is small, the speed of the short time is large, the speed is fast, and the small speed is slow.

2. First calculate the speed of cycling Time t1 = 40min = 2400s distance s1 = 14km = 14000m

v1=s1 t1=14000m 2400s is about and then calculate the speed of the 100-meter race: time: t2= distance, s2=100mv2=s2, t2=100m

Compare the speed of the two v1

(1) Reduce the error of the experiment and avoid chance.

2) Control.

1. Germination rate The lowest concentration has a high germination rate.

2. Avoid chance controls.