Physical problems knives in the hand .

This involves an inclined plane problem. The knife is placed on the hand, although no external force is exerted, but the gravity of the knife itself still acts on the hand, but at this time, the knife splits greatly, so it does not hurt the hand. When the knife is sliding, the knife splits smaller, that is, the knife becomes faster, so the hand breaks.

That's why butchers all cut meat with knives instead of knives. Note: The angle of the blade, the larger the angle, the blunt the knife.

Sliding is cutting very few muscle fibers, and putting it on the hand without bleeding even if you put a little force on it, is equivalent to cutting a lot of muscle fibers, just like a chopstick is easy to break and a chopstick keeps breaking.

There is a frictional effect! Besides, the knife slips through the hand, which creates some pressure! Some of the pressure is not straight to the hand, it may be in other directions, but it is still acting on your hand!

Friends who drink porridge answer better!

Straight chopping and oblique chopping, when the thickness of the knife changes, the length of the route is different, so that the angle of the cutting edge is different, the more oblique, the smaller the angle, the sharper!

I know the real answer to this question. The blade of a knife appears to us to be a sharp, straight face, but it is not. If you look at it with a magnifying glass, the blade of the knife has one tooth after another under the magnifying glass, like a saw.

When it comes to saws, you probably understand that when you put the saw on your hand, your hand won't hurt you, but as soon as you pull your hand, it will bleed.

I think that's how Master Luban invented the saw back then.

If you have a magnifying glass on hand, you'd better check it, preferably ten times more.

Calculate the second question first, calculate the velocity of a and b according to the conservation of mechanical energy, ma r 2-mb r 2 = 1 2 (ma + mb) v 2, calculate v.

According to the kinetic energy theorem, the work done by the rope on B minus the work done by gravity on B is the kinetic energy that B has.

(1) Question: Why are the spouts and body of the pot equal in height?

Answer: The spout and body constitute the communicator, according to the principle of the communicator, if the height is not equal, it will only cause a waste of materials, and can not be filled with more water

2) Question: What is the function of the small hole in the lid of the pot?

A: The small holes communicate with the atmosphere and allow water to flow out unobstructed

3) Question: What is the physical knowledge involved in the design of the device schematic diagram of the dairy cow automatic water feeder?

Answer: There is the problem of liquid pressure and pressure, as well as the principle of the communicator, so the answer is: why is the spout and body the same height; The spout and body constitute the communicator, according to the principle of the communicator, if the height is not equal, it will only cause a waste of materials, and can not be filled with more water

In fact, this kind of ** is not easy to use, because you can't find a good support point!

There is something called a finger tiger that is very used, and it is used in ordinary fights.

That is, 4 fingers (except the big finger mother), each with an iron ring. Very practical.

It should be called a brass knuckle sleeve, like four rings connected together, each with steel nails on it.

It should be called a "hand stab", which has a grip that can be held in the heart of the fist, and the blade of the knife sticks out between the fingers of the index and middle fingers.

It's an iron finger, don't believe it, search the Internet.

It is generally called a fist spur and has a different shape due to the different manufacturers.

Suppose the surface is level, but elastic.

After the meat is dented due to the force, the two flanks of the knife generate a pressure at both ends that is much greater than the pressure of the blade, and this force is easy to decompose. Then two conclusions are obtained: the thinner the knife, the greater the flank pressure, the easier it is to break; The deeper the depression, the closer the direction of the flank pressure is to the horizontal flank pressure, and the greater the flank pressure, the easier it is to break.

Then in the process of horizontal knife transfer, the positive pressure of the blade remains unchanged, the thickness of the knife does not change, and the ** through which the knife passes gradually appears depressed from the level, but the degree of depression does not exceed the initial moment.

To sum up, I don't think ** will break. If the theory is not guaranteed, please do not experiment.

Look at the pressure of the blade on the arm, there is friction between the blade and the arm. The pressure is high, and the friction is also high.

Because it is rectangular after cutting, it can be imagined that the cutter is chasing the glass, therefore, the minute velocity of the cutter in the direction of the glass is equal to the speed of the glass, therefore, assuming that the glass goes from left to right, the direction of movement of the cutter is the route of the angle of the glass forward speed. The time has a root number, and it is difficult to list it.

Knowledge of mechanics on kitchen knives.

As soon as it is mentioned"Knives"This word is really known to everyone, and everyone knows it. "Knives", every household has it, and it is essential, and it is used almost every day to cut, cut, chop, and cut food, and that's what we're going to study now"Knives"Relationship with mechanics in physics.

The structure of the kitchen knife: The kitchen knife is mainly composed of three parts: the blade (1), the blade (2) and the handle (3).

First, the blade. The blade of the kitchen knife is used to cut food, the cross-section of the blade is a triangle, and the tip of the knife is very sharp, that is, the top angle of the triangle is very small, when we use the kitchen knife to cut the food, when the force is applied to the blade f, firstly, this force acts on the food, produces great pressure on the food, so as to cut the food, at the same time, this force will produce two effects, which makes the pushing force f1 and f2 on both sides of the blade are the two components of f, if the cross-section of the blade is an isosceles triangle, According to the parallelogram rule of force, we know that f1=f2=f 2cos. Therefore, the smaller the blade, the sharper the blade, the easier it is for the kitchen knife to cut food, but the strength and rigidity of the blade should be relatively weakened, and the purpose of sharpening the knife is to reduce the top angle of the blade.

Second, the blade. Different kitchen knives, the shape of the blade is very different, the commonly used kitchen knife, the blade is rectangular, the thickness is generally about 1mm, the meat knife (meat axe) for chopping meat, the blade is arc-shaped, and very thick, as shown in the figure, the fruit knife, the overall is smaller, the blade is long and narrow, and the texture is lighter. The shape of these knives is determined by their use, for meat knives, because to cut meat, at the same time, to stomp on the bones, so a larger mass knife is required, when the kitchen knife goes to cut meat at a certain speed or"Stomping"When the meat is bone, the kitchen knife with a large mass will have a greater force on the food, so as to achieve the purpose of cutting the food, and for the fruit knife, the fruit is cut, which is relatively brittle, so when cutting, it does not need a lot of force, so the fruit knife with a light texture has little inertia and is easy to operate.

3. Knife handle. If you use a knife"Stomping"When the tip of the knife touches the bone, the hand will feel the handle shake downwards and vice versa, and there is a position where this point on the knife is stomped on the object, and it feels very easy to touch, because there is one for any object that rotates around the axis"Strike Center", when the line of action of the force passes"Strike Center", the shaft of rotation is subjected"Blows"The force of action is zero, and the blade of the meat axe, which butchers often use to stomp meat, is round, which is intended to be in"Stomping"Meat bones, no matter which part of the force is in contact with the meat bones, can ensure that the force of the meat bones on the knife is basically through the handle as the axis of rotation? quot;Strike Center", so that you can reduce the effect of the knife opponent when stomping.

In our daily life, mechanical phenomena can be seen everywhere, so the understanding of force is particularly important, through this research, it is a certain practice process of the mechanical knowledge we have learned before, so that we have a deeper understanding of the mechanical knowledge, and play an important role in the future study of physics.

Ask the knife you really asked the wrong person to pull, I know that a person must know Xiao Li

Landlord, I'm absolutely talented.,,Why don't you study the feeling of a kitchen knife and a fruit knife into your stomach.。

This problem needs to be considered for the internal resistance of the two meters. Otherwise, there is = ohms, and the second condition is meaningless.

The power supply EMF should be treated as constant. When switch S2 is connected to B, the voltage is expressed as . The crack pressure of the electric power is the power electromotive force.

When S2 is connected to A, the voltage is expressed as . Therefore, the first difference closes at this time the ammeter carries a voltage of.

v。And in this case, the current is expressed as . Therefore, the internal resistance of the ammeter is.

ry = u i = = 19 6 ohms.

When the double-throw switch is turned on B, the indication of the ammeter is and the indication of the voltmeter is.

ry) =rx + ry = = 128 13 ohms.

rx = 128 13 - 19 6 = 521 78 ohms = ohms.