When I m bored, I think of a problem, or physics

It's almost exactly right, the ones on the upper floors don't care about them.

At university, you'll learn the differential form of the gravitational force calculation formula (not the one in your middle school textbook), which is a little more complicated, and you can use this formula to calculate the gravitational force of one object on another, knowing the position and shape of both. (This is an exercise that all first-year physics students will encounter.) ）

This calculation illustrates the principle you said: "If you take out a concentric sphere at the center of the sphere, then the gravitational force in all directions is completely canceled out in this hole, and it is completely unaffected by gravity." ”

The reason why it is not completely true is that the earth is not perfectly spherical, so the gravitational force in all directions is not perfectly equal, there is always some surplus, but the remaining part is also very weak.

However, there must be a point inside the Earth where gravity is completely canceled out in all directions, and no gravity is felt.

The center of the earth not only has weight, but also the largest weight, but the center of the earth is surrounded by the relationship between mutual action and reaction force, that is, in the center of the earth will be gravity, or a pair of forces generated by each other, to compress into a small person smaller than a little finger.

I don't think there's a sense of weight (if you dig a hole in the center of the earth, there is insulation to keep out the heat and provide oxygen).

That's right, it's very good, this is a 12-year science comprehensive question in Hunan that you came up with.

Gravity is not all towards the center of the earth, gravity is the combined force of gravitational and centripetal forces, and only at the north and south poles is towards the center of the earth. The latter inference seems to be correct.

This requires high equipment from the rig ship, and the pressure underground. The temperature is very high, and the core of the earth is all magma.

1): y=45m, x=45 3

If the object is thrown from point A and then makes a flat throwing motion, then there is y=1 2gt 2 in the vertical direction to get t=3s

The bomb takes 5s**, then the time taken from pulling the string to throwing it is 5-3=2s2) after the object is thrown from point A and then making a flat throwing motion, then there is x=vt(t=3s) in the horizontal direction to get v=15 3m s

3) When the speed in the horizontal direction is equal to the speed in the numerical direction, the distance between the grenade and the hillside is maximum.

That is, v=gt calculates t=

1. To solve this type of problem, the main attention is to divide the velocity and displacement into the x-direction and y-direction calculation.

sin30°l=h→h=45m

h=1/2gt²→t=3s

t-t=2s

The displacement vector of flat throwing motion is used to decompose the problem.

2 cos30°l=x→x=45√3m

vt′=x→t′=15√3m/s

The displacement vector of flat throwing motion is used to decompose the problem.

3 v=gt′′→t′′=

It is also the decomposition of the use of flat throwing motion.

You said that you also give a picture and give points;

Alas!!!

Since the velocity of the bullet is very large, the drag force is also very large (the drag force is proportional to the nth power of the velocity), then the work done by the drag force will be very large. When the bullet returns to its original altitude, the displacement is equal to zero, the kinetic energy of the change in gravity is zero, and the work done by the drag force (i.e., the loss of kinetic energy or mechanical energy) is very much. The lethality will be greatly reduced.

This refers to a purely physical explanation, which is bound to differ from the actual situation.

2) Is the lethality of a bullet measured only by its velocity?

It's dangerous, as you said, there's still a lot of momentum when the bullet falls, and injuries still happen, you can look at the news.

Threaded lenses turn astigmatism into parallel rays.

Answer: This is capillary action, and the driving force is the surface tension of the water.

The strip of cloth is a silk fabric, and there are rich capillaries on the grinding bench, so the water gradually rises under the action of the blind plum capillaries.

The cloth strip is easy to infiltrate the object for water, and the liquid surface in the capillary is concave, that is, the surrounding is high, and the middle is low. The thinner the capillary, the higher the lifting height.

The velocity hunger difference of the ball falling to the lowest point is 0, so the work done by the electric field is equal to the work done by the gravity of the ball, so mgl=eql,eqd=uq,e=u d=200 ,q=,8*10 6c,because eq=mg,so the direction of the resultant force is 45° obliquely downward and vertically,so the speed is the largest when the reverse extension line coincides with the o point in this direction,so mgl 2=mv 2 2,v=

Isn't Newton's first law written: Any object that is not subject to any external force always remains in a state of uniform linear motion or a state of rest until an external force forces it to change this state. Then Newton's first law can be extended that if the sum of the external forces on the object is 0, then the object is also moving in a straight line at a uniform speed or at rest.

An object can move in a straight line at a uniform speed on a horizontal plane, either with 0 friction or 0 with an external force (i.e., the resultant force of friction and other external forces is 0).