"Today, we`re going to have an experiment!"

Which stuff floats or sinks?...

A ball floats!

How about an empty pet bottle...?

Floats!!

Then, how about a pet bottle with some water...?

"I think this is going to sink."

"I think this bell is going to sink
because it looks heavy."

"It floats!!, why!!?"

They look very interested in the experiment!!