In terms of meaning, there is no difference. For example, you can say, `The absent minded professor had put his shirt on backwards.’ It is also possible to use `backward’ in the sentence. The British generally tend to use `backwards’, while the Americans use `backward’. It is very much like the use of the words `toward’ and `towards’. Americans prefer `toward’, while the British favour `towards’. When used as an adjective (that is when used before a noun), however, you can only use `backward’. In the sentences given below, we cannot use `backwards’.
*The children walked out the cave without a backward glance.
*Sandhya took a couple of deep breaths before doing her three backward flips.