Is it possible? First of all, in terms of density, the volume of drowning water with the same mass is at least 2-5 times that of lead. The larger the volume, the greater the water resistance in the water and the slower the sinking speed. A friend suggested that the bullet-shaped shape has little water resistance in downhill water, which is correct, but what is the sinking speed? In fact, it is only a few meters per second. According to fluid mechanics, in this low-speed range, the most important determinant is the volume (or the density of the object), not the appearance, except, of course, making the object into a particularly outrageous shape (such as making it into a sheet or a cake).

2. The famous brand Abo can be accurately balanced to 5- 10 cm underwater, and it will not float or sink, but the inferior brand will not.

There are two problems here. Can Po not float or sink when it is 5- 10 cm underwater? Is it possible?

I said absolutely impossible. According to Archimedes' principle, the buoyancy of an object is equal to the volume of boiling water it discharges.

In an ideal state, when there is no wind or waves, we adjust the lead clip accurately, and a Bo is completely submerged in the water. The gravity of the whole fishing group = the buoyancy of Abo's image. At this time, a Bo can hover in the water, but note that a Bo can hover at any depth, instead of underwater 5- 10 cm. But due to the influence of wind and waves, this ideal state is impossible. Generally, we can only adjust the head of a Bo to a few millimeters above the water, or let the gravity be slightly greater than the buoyancy (that is, what we call negative buoyancy).

A friend said, can ABO, a miscellaneous brand, reach this level?

Unless a miscellaneous brand is made of special substances, the buoyancy it receives in the water is fixed (except, of course, the poor quality will slowly absorb water). Uncle, a miscellaneous brand can also be balanced.

As an introduction, I hope my friends will abide by the knowledge of physics when fishing and thinking.

1. Basic concepts:

Collision generally refers to the process in which two or more objects approach each other or contact each other in motion, and intense interaction occurs in a relatively short time.

Collision will obviously change the motion state of two objects or one of them.

The collision process is generally very complicated, and it is difficult to analyze the process carefully. However, because we usually only need to know the changes of the motion state of the object before and after the collision, the role of external forces can often be ignored for the colliding object system, so we can use the conservation laws of momentum, angular momentum and energy to solve related problems.

2. Features:

1) The collision time is extremely short.

2) The collision force is large, the external force can be ignored, and the momentum of the system is conserved.

3) There will be a limited change in velocity, and the displacement before and after the collision can be ignored.

3. Analysis of collision process;

Discuss the collision process of two balls. The collision process can be divided into two processes. At the beginning of the collision, the two balls squeeze and deform each other, and the elastic restoring force generated by the deformation changes the speed of the two balls until the speed of the two balls becomes equal. At this time, the deformation is the largest. This is the first stage of the collision, called the compression stage. After that, because the deformation still exists, the elastic restoring force continues to act, so that the speed of the two balls changes and there is a trend of mutual contact, and the compression of the two balls gradually decreases until the two balls are out of contact. This is the second stage of the collision, called the recovery stage. The whole collision process ends here.

4. Classification: According to whether energy is conserved during collision.

1) complete elastic collision: the kinetic energy of the system is conserved before and after collision (it can be completely recovered);

2) Inelastic collision: the kinetic energy of the system is not conserved (partially recovered) before and after collision;

3) Completely inelastic collision: after the collision, the system moves at the same speed (it cannot be restored to its original state at all).

Second, completely elastic collision.

After the collision, the sum of the kinetic energy of two objects (that is, the total kinetic energy) has no loss at all. This kind of collision is called a completely elastic collision.

Key points of solving problems: conservation of momentum and kinetic energy.

Problem: Two balls m 1, m2 collide in the center, the velocity before collision is 0, and the velocity after collision is 0.

conservation of momentum

( 1)

Conservation of kinetic energy (2)

Pass (1) (3)

By (2) (4)

By (4)/(3)

Or (5)

That is, the relative velocity v 10-v20 before the collision is equal to the relative velocity v2-v 1 after the collision. According to equations (3) and (5), it can be solved as follows:

Discussion:

When two balls collide, exchange speed.

L, then, rebound means that the mass is large, and the original stationary object remains motionless after collision, and the velocity of the object with small mass is equivalent to the opposite direction after collision.

L if m2

3. Completely inelastic collision.

If two objects move at the same speed after collision (that is, they will not separate after collision), this collision is called completely inelastic collision.