The difference between pop and rock

GrandDaughter1 is in the car with me.
She says, 'Granny, what's the difference between rock and pop?'
'Um, well, rock is usually noisy and bangier while pop is a bit sweeter.'
(She chose the right person to ask with my wide-ranging musical knowledge.)
'I hate pop,' she declares.
'What about ... Katy Perry (the only musician I think we might both know)? She's sort of pop.'
'No, she's not! She's rock.'
'Oh.'

We're on our way to a holiday art workshop in the Dylan Thomas Centre. When we get there GrandDaughter1 decides she isn't going to talk to anybody except me so we find a place at a table and start to make journal covers. 

After a while GrandDaughter1 condescends to talk to the very helpful and friendly art tutors on hand. I can understand her reluctance: I'd rather be left alone than having to keep talking to people who want to offer ideas and suggestions.

GrandDaughter1 knows what she wants to do: have an undersea-based cover so when she grows up and can dive she can record all the creatures she sees and here it is.

And my rather pathetic effort!