Biological cells move, divide, change their shapes, adhere to their neighbors and environments to form tissues and organs. These phenomena are essential for a wide variety of biological processes during morphogenesis for example but their mesoscopic origins are often yet not clarified. To characterize them, out-of-equilibrium dynamics can be studied with physical experimental designs and associated theories. These topics have triggered new physical formalisms which call for original experimental calibrations and tests associating tightly quantitative biology with the design of new setups and models for living matter. I will illustrate these experiments of biological physics with two examples : spontaneous breaking of symmetry for single cell motion and collective effects in elongation of epithelial colonies. Both will show that basic principles in physics can be used and challenged to unravel new cellular mechanisms with physiological relevance.