The two sides of taichi: 

Earthwork: connecting to, and exchanging energy with, the Earth beneath your feet in order to develop a stable but fluid foundation. 

Heartwork: connecting to, and communicating with, other human beings, especially ones who threaten to upset your balance.

Both connexions are physical and energetic, and involve the same principles of equilibrium, relaxation, softness, yielding, elasticity, spirit, etc.