Some doubts about the potential energy of gravity in physics

Calculate the height difference of the center of gravity. The height difference at the top of the plank is the same as the height difference between the center of gravity of the plank. The reference book is written this way because it is obvious.

Liquid column Reference book Yes, you can think of it as half of the liquid column on the right side that is higher than the left column and placed on the left.

If you have to analyze according to what you said, you can analyze quantitatively, that is, calculate the increase and decrease of the gravitational potential energy of the liquid column, and you will find that it is reduced.

The first question is because the center of the wooden block has not changed, so you can look at any point, and the center of gravity has changed, you must look at the center of gravity, second, to give you an example, two buckets in one water weighs two kilograms, two meters high, the gravitational potential energy is 20, the other weighs four kilograms and is four meters high, the gravitational potential energy is 80, and the average height is three meters, and the two gravitational potential energy is 90, so it is reduced.

Equivalence, the change in the center of gravity must be correct.

The various methods in the two questions you gave are equivalent to the change in center of gravity.

Obviously, in the first part.

The second part is the typical equivalence, and as for what you said about the left addition has been recorded in his practice, the so-called right side moves to the left side, isn't there already too much left side?

The first one, in general, should be calculated as the height difference of the center of gravity, since the height difference of the center of gravity in the first question is equal to the height difference from the top to the top, so it can be expressed like that.

Although the communicator goes down and rises, in general, the overall center of gravity decreases, so the total gravitational potential energy decreases.

In the first question, the tutorial book ignores two points: the thickness of the plank, and the buoyancy of the water on the board, so it is only an approximate algorithm, and there must be loopholes under careful study.

In the problem of the communicator, the decrease in the potential energy on the left side is greater than the increase on the right, and the total potential energy is reduced. Where does the reduced potential energy go? It is converted into kinetic energy for water flow.

Vector: There is a size and a direction.

Scalar: There is a size and no direction.

Gravitational potential energy has magnitude, but it has no direction and is said to be a scalar quantity.

For gravitational potential energy, its magnitude is determined by the relative position of the object on the earth and the ground. The greater the mass of the object, the higher the position, and the greater the ability to do work, the greater the gravitational beam brigade potential energy of the object.

Linear velocity is a physical quantity that describes the speed and direction of motion of a particle that moves as a curve.

v = s t (s is the arc length) = 2 pair t (t is the period) = 2 pairf (f is the frequency) = 2 pairn (n is the rotation speed) = rw (w is the angular velocity slag rent) =

Direction: The tangential direction along the motion track.

If the object moves in a circular motion and the linear velocity is equal everywhere, this motion is called uniform circular motion. It should be noted that the direction of the linear velocity of the circular motion of the uniform stool velocity changes at the moment, so it is still a variable velocity motion, and here "uniform velocity" means that the velocity is constant.

When the gravitational potential energy is closed, it belongs to a physical quantity, and it belongs to a form of energy, and when we study the mechanical energy of the object, we must study the gravitational potential energy of the object.

The gravitational potential energy is defined as the weight mg of the object multiplied by the centroid position h

For the weight m(i)g of the part marked i, the centroid position h(i), there is:

e=g m(i)*h(i)=g [ m(i)] Noting that the curly braces are the definition of the position of the center of mass, it is proven.

Definition of gravitational potential energy: The energy that an object has due to being lifted is called gravitational potential energy. The greater the mass of the object and the higher it is lifted, the greater its gravitational potential energy.

The gravitational potential energy of an object decreases mgh: it should be that the kinetic energy of the object with increased mghb decreases fh: the force mg-f, so the kinetic energy decreases (mg-f) * the mechanical energy of the hc object increases fh:

The increase in mechanical energy is the work done by an external force in addition to gravity, and the increase in gravitational potential energy of an object for f*hd is less than the decrease in kinetic energy: mgh<(mg-f)*h is obviously not true.

So choose C

Kinetic energy is related to the mass and speed of the object; Gravitational potential energy is related to the mass and height of an object; The mechanical energy of friction is converted into internal energy.

During motion, the velocity and mass of the object remain constant, so the kinetic energy remains constant; The mass of the object does not change but the height decreases, so the potential energy becomes less; In the process of motion of the object, it is in the constant friction of the air, and the total heat generated is increasing, so the internal energy becomes larger.

ep=m*g*h

It is to specify the position of 0 meters at a relative height.

The mass of the object m multiplied by g times the relative height, which is the energy (possibly -energy) that the object has at a relative height of 0 meters

aThe magnitude of the gravitational potential energy of an object is determined by the magnitude of the gravitational pull of the earth on the object and the relative position of the object on the earth and the ground. The greater the mass of the object, the higher the position, and the greater the ability to do work, the more gravitational potential energy the object has.

To some extent, when the altitude is constant, the greater the mass, the greater the gravitational potential energy; When the mass is constant, the higher the height, the greater the gravitational potential energy.

ab, analysis: c gravitational potential energy can be negative. d The concept of gravitational potential energy is that the energy that an object has when it is raised is called gravitational potential energy, and if it stops at a certain point, then it has gravitational potential energy and does not do work on the object