Sun Tai chi is the newest of the 5 main Tai Chi styles. It was created by Sun Lutang in the early 1900s. Sun Lutang was already proficient in the other two Chinese internal martial arts styles of Xing Yi and Bagua. He learned Wu(Hao) style Tai Chi from Hao Wei Zhang. He also studied the Yang style with Yang Cheng Fu. The Sun style is different from Yang and Chen styles. Only rarely do the legs separate farther than shoulder width. The original form created by Sun Lutang was the Sun 97. It has the same pattern as the Wu long form which is patterned after the Yang 108 form.
The Sun 38 form was put together in Beijing by a University Professor, Li Deyin. The movements are taken directly from the original Sun 97 form. Like the Yang 24, it is learned in a much shorter period of time than the long form and can be a stepping stone to the longer form. The 38 form is not an "easier" form, it is just shorter.
Below is a link to my page which has the list of movements and a video of the Sun 38 form.
38 from list and video
There are two facets of Yang style Taiji that I think are genius. The first, every movement being coordinated with the breath and the second, all movements are performed at an even, slow speed. The benefits of these two factors are immense. But one thing that Yang Taiji lacks are silk reeling exercises. In Chen Taiji much emphasis is placed on these exercises, which helps the practitioner get in touch with the dāntián and learn to move and generate power from it. The dāntián is the area located below the belly button and is an energy center, sometimes referred to as the “sea of qi(chi)”.
In Yang Taiji, it is harder for practitioners to learn to move from the core and generate chi from the dāntián.
One of the best ways I’ve found to begin feeling the movement in the dāntián is by practicing stationary cloud hands, yún shǒu. Standing in a comfortable horse stance, relax into the circular arm movements, allowing the body to move the arms. Your weight shifts from one leg to the other and your upper body turns slightly to the right and then to the left. Allow your breath to be natural and unforced. As you settle into the slow rhythm of the movements, become aware of the dāntián area. Feel how the dāntián perfectly generates each movement. Chi is not only sent out into the arms, but simultaneously down the legs in perfect harmony for proper execution. When the right arm goes down and the left arm goes up, there is a turning in the dāntián. Hold your attention on the dāntián throughout the exercise. With persistent practice you will begin to feel the dāntián in other Taiji movements throughout the form. Practicing cloud Hands for just a few minutes each day with the focus on moving from the dāntián will significantly improve your Taiji.
The Yang taiji 24 form was created by the Chinese Sports Committee in 1956. Four taiji teachers put it together from the Yang family 108 form. Being shorter than the long form, it is quicker to learn and to perform. It was promoted by the People's Republic of China for the population's general health and according to Wikipedia, also taught to internees at communist re-education camps. The form retains many of the movements of the long form, so it is not a simpler form in difficulty, just shorter.
Here is a link to a modern stylist performing the 24 form.
I changed the 24 form somewhat to be more in harmony with traditional Yang taiji. Also some moves are modified, for my older students so for example the snake does not creep quite so low. In traditional taichi we do not kick higher than the waist and the movements in general are more subtle.
Link to my 24 form.
Here's a picture of Yang Cheng Fu in "play the pipa" position. Pipa is pronounced (pee, with an upward rising tone and paw, another upward rising tone)
This Chinese woman is playing a pipa. You can see by her hand position why they named the moved after it.
Sometimes the taiji(pinion spelling) position is called "play the lute". A lute is an English Renaissance instrument that is similar to a pipa.