There are some situations about "swing" and "tilt" modern dance: (1) wiggle wiggle (2) pendulum swing (3) metronome swing defines the chassis as the crotch, and the crotch as the pelvis. The central axis is defined as the spine, and the spine is defined as a line from the tailbone to the back of the head. Note that the coccyx is connected to the chassis (pelvis). "Swing" refers to the chassis. "Tilt" refers to the central axis. (1) Swing is the rotation or angular displacement of the chassis during the center of gravity flow, which is the definition of swing. Let's examine the angular displacement of the chassis. Theoretical mechanics divides the displacement of rigid bodies into linear displacement and angular displacement. Generally speaking, linear displacement is displacement without rotation, that is, all particles that make up a rigid body have the same trajectory. Popular understanding, angular displacement is rotation. There must always be a rotation axis, and the rigid body rotates or angularly moves around the rotation axis. The chassis can rotate or angularly displace in three orthogonal directions. The following three-dimensional coordinate system is established: the straight line through the two hip joints is the horizontal axis of the chassis in the left-right direction, and the chassis can rotate or angularly displace around such a rotation axis. The central axis is the vertical axis of the chassis, around which the chassis can rotate or angularly displace. The straight line perpendicular to the chassis and passing through the navel is the horizontal axis in the front-back direction of the chassis, and the chassis can rotate or angularly displace around such a rotation axis. There are some cases of "swing" in modern dance: (1) The swing swing chassis rotates or angularly moves through two hip joints in a straight line, which is called swing swing, and samba often appears in Latin dance. I think this swing is in samba's genes. In modern dance, the swing appears after the low, which is the first step of each bar. But here I want to point out one thing: the low swing. Swing in the front and back direction. Notice that the swing has no hips. (2) The rotation or angular displacement of the swing chassis with a straight line perpendicular to itself and passing through the navel as the axis is called swing. The pendulum swing is characterized by "high hip and low hip", that is, the left and right sides of the hip are always high and low. The second step of the waltz is the pendulum swing. The pendulum swings in the left and right directions. However, it should be pointed out that it is not a simple left-right direction, that is, it is not a simple horizontal direction, but it is accompanied by a little forward and backward direction, so it is an oblique pendulum. (3) The swing of the external metronome, especially the external lady, often occurs. Metronome swing is actually pendulum swing, just a special form of pendulum swing. Therefore, it is necessary to clarify the concept of "reflexivity". The reason why people are obsessed with the concept of "reflexivity" is that people lack theoretical mechanical knowledge about angular displacement of rigid bodies. As I said before, the chassis can rotate or angularly displace in three orthogonal directions. Wherein, the central axis is the vertical axis of the chassis, and the chassis can rotate or angularly displace around such a rotation axis. The essence of "reflexivity" is that the chassis rotates around the central axis or deviates from the angle. Imagine an arrow perpendicular to the chassis and passing through the navel. The arrow points outside the body. In differential geometry, the direction of the arrow is called the outer normal direction of the surface. When there is no reflexivity, the arrow points straight ahead. When reflexive, the arrow no longer points straight ahead and deflects. In other words, the direction of the plate has changed. The second step of the waltz is not reflective. The second step in some programs based on measurement steps is not reflexive either. At this time, "a little small front-back direction" is not reflexive, because the normal direction outside the board (the direction in which the arrow passes through the navel) has not changed. But the lateral position must be reflexive, and it is reflexive to a great extent. Therefore, the pendulum swing at this time, of course, is still in the left and right direction for the chassis itself, that is, the high and low hips, but due to a great degree of reflexivity, for the human body, for the onlookers, the high and low hips appear in the front and rear direction. The metronome swing is a special one among the three kinds of swings, because it is related to tilt, so we must explain the tilt clearly and come back to the metronome swing. (2) About "tilt" and "tilt" are all aimed at the central axis. The definition of "tilt" is: "tilt" refers to the state that the upper section of the central axis (above the diaphragm) is not perpendicular to the floor. Tilting is caused by swinging. Swing is the cause of tilt, and tilt is the result of swing. Swing is an action, not a sport. Swing is the way the center of gravity flows. Tilting is a kind of posture, which can appear in the process of action (the center of gravity flows) or at rest (the center of gravity stops flowing). The tilt at rest should be the continuation of the tilt during the action or the retention of the tilt during the action. If there is no inclination in the movement process before stopping (center of gravity flow process), but only after stopping (center of gravity flow process), then it is completely wrong to deliberately "do" inclination, which violates both scientific laws and aesthetic laws. Regrettably, this was achieved in the epidemic and plague that swept through China. They publicly declared that the second step of the waltz dance was "flattening", that is, not swinging, and deliberately "tilting" until the end of the second step. I hate this practice. The reason why the epidemic plague is "peaceful" is completely wrong, because they separate the cause of tilt and tilt, that is, they "do" tilt in isolation. There is no reason, only the result, and that result can only be wrong. Tilting refers to the state that the upper section of the central axis is not perpendicular to the floor. This state, this posture is the result that the chassis is ahead of the central axis, that is, the chassis is ahead of the upper body, which leads to the backwardness of the upper body. So if there is a tilt and there is no swing, it must be fake, fake and deceptive. This is why epidemic plague is harmful to people. It should be noted that the word "high position" should be added to the complete definition of tilt: the complete definition of tilt is: tilt is a posture, which refers to the state that the upper section of the central axis is not perpendicular to the floor at a high position (including the rising process from low to high). This posture is the result of the swing of the center of gravity flow, that is, the chassis is in front of the central axis (the chassis is in front of the upper body) and the upper body is in the back. When we start swinging in the low position, we need to have high and low hips first. Because the hips are high and low, the upper section of the central axis is not perpendicular to the floor, but there is no swing at this time, so it is not appropriate to call the upper section of the central axis not perpendicular to the floor as inclination. The popular understanding is that when I do the second waltz swing, I like to shout loudly: "I am not a telephone pole, I am a willow!" " "Now let's go back to the metronome swing: in the outer position, especially the lady in the outer position, the metronome swing often happens. Metronome swing is actually pendulum swing, just a special form of pendulum swing. The second step of the waltz is not reflective. The second step in some programs based on measurement steps is not reflexive either. At this time, "a little small front-back direction" is not reflexive, because the normal direction outside the board (the direction in which the arrow passes through the navel) has not changed. But the lateral position must be reflexive, and it is reflexive to a great extent. Therefore, the pendulum swing at this time, of course, is still in the left and right direction for the chassis itself, that is, the high and low hips, but due to a great degree of reflexivity, for the human body, for the onlookers, the high and low hips appear in the front and rear direction. The difference between the tilt caused by metronome swing and the tilt caused by the second swing of waltz square step is as follows: the second swing of waltz square step appears in the closed position, and the metronome swing appears in the outer position. The second pendulum of waltz square step is not reflexive, and the metronome pendulum is reflexive to a great extent. In the second step of the waltz, the swinging hips are in the left and right direction, and the swinging hips of the metronome are in the front and back direction. In this way, the tilt caused by the two swings has the above differences accordingly. In a large number of dance papers, I have discussed in detail the three elements in mechanics: inertia, elasticity and viscosity, and also discussed in detail the viscous lag in dance, or the lagging follow of the upper body relative to the chassis. In fact, tilt is the posture that the upper part of the central axis is not perpendicular to the floor because it lags behind the chassis during the swing. In other words, people pay more attention to the second swing of the waltz and the tilt caused by this swing. Since the object of swinging is the chassis, it is called pendulum swinging, which is the so-called simple pendulum in physics, which is what Teacher Wang said, that is, the upper end of the object is fixed and the lower end swings. The pendulum swings. Some teachers like to touch their heads with the fingertips of one hand when teaching this swing, that is, imagine their heads hanging from the ceiling, their central axis is a rope, and the bottom is tied to the chassis, that is, imagine themselves as a so-called simple pendulum in physics. The tilt caused by the side swing and the sticky characteristics of the upper body lag are more obvious. Therefore, people pay more attention to tilt, that is, the phenomenon that the upper body lags behind the chassis can catch people's eyes better. That's what your husband said. " Sloshing generally means that the lower end of the object is fixed and the upper end is sloshing. "This phenomenon is more vivid than the metronome used by music professionals, so it is called metronome swing.