Doubts in reality, doubts in physics

If you have to believe that there is, there must be!

I used to doubt like you whether there is really perfect love in the world, but whether you doubt it or not, you can't change anything, so what you can do is to adjust your mentality and truly believe in everything that is beautiful in the world. Believe in the best of all. The squalor and filth of reality are unacceptable, but believe that in this world, the mainstream is beautiful.

Be sure to believe in this. In this way, you can open your heart to everyone around you, and you can win your family, friendship and perfect love.

Love is originally a luxury, not a necessity, if there is me, if there is me, if there is none, it will be my life;

What is perfect in love? Is it always sweet and sweet, is it always vigorous? is plain and bland, and the stream flows for a long time; Is it a double stay and a double flight, and they stay together all day long? The two places are lovesick, and it is not bad to feel each other's existence with their hearts;

The question is not whether there is really perfect love in the world, and even if there is, what is the point if she does not belong to you!

Maybe it's actually you who are afraid of being hurt, so you question love and don't let it get close;

Relax your mind and tell yourself, I believe in love, I love him and her, and love itself makes you happy; Even if one day love flies away, or betrays, you can wipe away your tears and say to yourself: At least this love has accompanied me for a while, and I have love; I believe in love, only because of love itself, because love makes me happy, not because of anything else.

May you find a person in the vast sea of people who makes you feel at ease, and it will be a very happy thing.

Yes, but you can't see it. Just mind your own business, don't worry too much, what should come will always come!

Excrete emotions:

1.Find a place where no one is and yell.

2.Find a doll (or something that can be replaced) and have a big fight.

3.Listen to the light ** relax and go.

4.Distractions such as watching TV series, movies, or going to play.

Hungry, hungry, hungry ......Brother Ren, you think too much......

You are right, each jump cycle, the force analysis is as follows: the foot and the ground contact force (this is the process of overcoming gravity to do work) - make people jump off the ground (the instantaneous kinetic energy is the largest, only subject to gravity) - the highest point (the maximum speed of potential energy is 0) - descend to the ground (potential energy is converted into kinetic energy), because the process is more complicated, the specific foot climbing force can not be known, all we can consider from the perspective of ability transformation, reaching the highest point potential energy is the largest, which can be understood as the rising time and the falling time are equal, Each movement cycle is 1 3 seconds, the movement time is 1 5 seconds, and the descent time is seconds, according to p=f*v, it can be known that the work done to overcome gravity is:

m*g^2/2=2500j

Your understanding is correct.

In order for a person to overcome gravity to do work, he must be subjected to an upward force, and to meet this volume, the human foot is required to be in contact with the ground. Therefore, the time for a person to overcome gravity and do work is the time for a person's foot to contact the ground.

This is the work done by the athlete overcoming gravity, so you should count the work done by gravity, otherwise how do you count the work done by the athlete, do you know the amount of force used when contacting? Obviously, that force is not gravity.

This formula applies to purely resistive circuits, where electrical energy is completely converted into heat.

Leave it to the master to answer, make a mark and I will learn.

The v-t image describes the change of velocity with time, and on this image we can represent the displacement by the area enclosed by the image and the time axis, so if we want to see the pursuit problem through this image, we can only judge the change in distance by looking at the difference between the areas of the two images;

The velocity of point A and point B are instantaneous velocities, which correspond to the velocity value at a certain time (time point), which is the state quantity, and the average velocity is the response of the velocity in a period of time, which is the process quantity, and they cannot be replaced;

Acceleration is the rate of change of velocity, which is equal to the amount of velocity change divided by time, which is similar to the power in junior high school, that is, as long as the physical quantity of the rate is mentioned, it describes the speed of change.

As for the difference and connection between several physical quantities, it is not clear to you here, but it depends on your workbook, and the explanation before the exercise is very clear, so I will explain it briefly here:

Speed, in high school is generally instantaneous speed, for example, someone looks down at the speedometer during driving, and at this moment shows 60 miles, then its instantaneous speed is 60 miles, but it only describes the moment at the moment, before and after it has nothing to do with it, the average speed is v=x t, in fact, we can write it like this v=(xt-x0) (t-t0) that is, the displacement passed per unit time, it is a process quantity, and the average speed of the process of leaving the motion does not exist, He can't describe how much the speed value is at a particular moment, it reflects the speed of the whole journey.

Average velocity is actually the concept of speed in junior high school textbooks, that is, distance divided by time.

Since it is a change, the velocity value before and after it must be different, so the difference between the velocity value before and after is the amount of change.

The rate of change of velocity is acceleration, and this concept will not be repeated.

You've worked so hard to type so many words, I won't fight with you, hehe.

The first: not to use the ground as a reference, but to the object being chased. When the gradual velocity of the small velocity and the large velocity are equal, the relative velocity is the process of going from the maximum to the zero.

So the relative displacement is equivalent to a uniform deceleration of linear motion (between two objects), and when the velocity of the former is greater than the latter, the relative velocity is negative, and then the relative displacement decreases. A bit abstract, you think about it, pay attention to the relative velocity. The second:

The average speed between ABs? Is there such a statement? I don't know what it is.

Velocity: Usually based on the ground as a reference, and bit removal is defined by time, which is the amount of displacement per unit of time, with direction and magnitude. The amount of change in velocity, which is the amount of acceleration, the amount of change in velocity per unit of time, has direction and magnitude.

The average rate is the size of the distance per unit of time (the distance has a turn, the displacement has no turns), only the size, no direction. And so on. First of all, we need to separate vectors and scalars!

It can only be said that the change of velocity and velocity is related to displacement, and the rate of change of velocity and velocity is related to the distance, which is not the same. The change in velocity is multiplied by time to get the velocity, and the velocity is multiplied by time to get the displacement, so the change in velocity increases the effect of time on the displacement in a square.

yeah？

Don't go down to the pores, draw a schematic diagram of the force, direction and force. Holding a cup in your hand is still a force in the final analysis. Forces are interactive, and it is friction that keeps the cup from falling in your hand, and this friction is mainly due to the gravity of the cup.

If your hand is more forceful, the cup is less likely to fall off if there is a contrast, for example, someone pulls the cup with you. When no one pulls with you, your force is mainly applied to the cup surface and pressure inward, and your hand receives the resistance of the cup to you (please refer to the experiment of pushing the wall).

The force decomposition shows that the friction force is upward, and the pressure given by your hand is to the cup, and the friction of your hand is unchanged, just like if you hold a plastic cup, holding it hard will only deform it, and it will not be deformed if you hold it lightly, but it will not fall.

This is the static friction force, the cup is balanced by the force in the hand, the friction is equal to the gravity, and the tightness of the grip only increases the maximum static friction, which is not easy to fall.

The cup is stationary, so the force is balanced, the gravity and friction are equal, the gravity is unchanged, and the friction is naturally inconvenient. And because the cup is stationary, what is subjected to is static friction, not sliding friction, which does not satisfy f= n

Conceptual error.

The actual frictional force is equal to the gravitational force of the cup (or other force that wants it to change its state of motion).

You're talking about maximum friction (you won't be able to hold the cup if the external force exceeds the maximum friction).

No matter how you shake it, it's still a hand, ......Isn't it just that you hold the cup and don't let it fall, and it always has to be equal to the gravity of the cup to be still

Of course, there is a difference between this,,, uniform motion is of course balanced by force or without force, and the force of variable speed linear motion must be forced,,, by the force along the straight line, but the direction depends on the acceleration and deceleration,,, as for the size of the force, this is not easy to say, according to this condition can not be found,

The force is always 0 because it has no mass, f=ma, m=0, there is no difference between the two cases.

The state of motion can be divided into uniform linear motion and accelerated motion (including variable velocity and change of direction), so the two states of motion are different.

When moving in a straight line at a uniform speed, the rope is not balanced by an external force or an external force, and when it moves at a variable speed, it is subjected to an external force, and the magnitude of the external force is: ma. But I don't quite understand what you mean by not counting the quality, and there is no MA without counting the quality.

Hehe, it's interesting. This question needs to be calculated carefully, and the volume of water in the Erlenmeyer flask can basically be calculated according to the round table.

v=(1 3)* h*(r 2+r 2+r*r) (r is the radius of the great circle, r is the radius of the small circle, and h is the height of the water).

Then pressure = p*g*h = (m v)*g*h = m*g ((1 3)* r 2+r 2+r*r) )

You see, in an Erlenmeyer flask, the pressure at the bottom becomes independent of the height of the water.

If the water shrinks, then the radius of the garden above becomes larger, and the radius of the bottom surface remains the same, then the pressure becomes smaller according to the formula.

On the contrary, the water expands and the pressure increases.

Liquids also expand, but one of the characteristics of water is that it has the smallest volume at 4 degrees Celsius, that is, when it is lower than 4 degrees Celsius, the volume decreases as the temperature increases. As the volume changes, the liquid level height changes, and so does the pressure.

Before heating to 4 degrees, the volume is shrinking, the height is also decreasing, according to the formula, the pressure becomes smaller, to 4 degrees is the minimum, and then the temperature increases, the volume begins to increase, the corresponding height also increases, and the pressure also increases. Do you know the abnormal expansion of water?

If you want to calculate the answer accurately, you need to use calculus and temperature density curve equations to compare the relationship between density and altitude, but for high school knowledge, it should be explained by the knowledge point that water density is highest at 4 degrees Celsius.