A scalar, which is a tensor of rank 0, is just a number, e.g. 6

A vector, which is a tensor of rank 1, is a group of scalars, e.g. [1, 6, 3]

A matrix, which is a tensor of rank 2, is a group of vectors, e.g.

1 6 3

9 4 2

0 1 3

A tensor of rank 3 would be a group of matrix and would look like a 3d matrix.

A tensor is the general term for all of these, and the generalization into high dimensions.

A zero tensor is a tensor with all entries equal to zero.

tensor.

velocity is contravariant tensor becasue displacement tensor is contravariant.

Stress is a tensor because it affects the datum plane. When this is affected and it changes, it is then considered a tensor.