Normals of triangular faces are essential vectors in many areas of computer graphics. In this paper we will deal with methods for normal computation of triangles under linear soft-body deformation; i.e.; the triangles which deform in time so that each vertex travels independently along its linear trajectory. Linear deformation can be found in mesh morphing; cloth simulation; physical simulation; etc. We will demonstrate five different approaches for temporal face normal interpolation; one of them is new; and we will discuss their pros and cons.