The explanation is as follows:
Notes: Continual is often confused with continuous. However, the meanings of these two words differ significantly and they cannot be used correctly as synonyms. Continuous refers to an action that continues in an unbroken fashion, as a continuous hum or buzzing sound. Continual refers to a repeated action that is periodically interrupted, as continual complaints about the dog from the neighbors.Both of these adjectives come from continue, but the differ in meaning so much that they can not be used interchangeable, that is they cannot be synonyms. If I want to write that something happens without stop, then I use continuous.
- There was a continuous whistle in my ears while I had a cold.
- Her continous complaining made her uncomfortable company.
- He made continual use of the whistle to stop play.
- The protestors faced continual pressure from the police.