Amy and her younger brother Sam were on their way home after a walk when Sam exclaimed "Look Amy, that puddle outside our house is still there and it hasn't rained since yesterday!"
"That's because some soils don't let the rainwater through very easily." explained Amy.
"Why's that?" asked Sam.
"Tell you what, Sam, why don't we do a little investigation to find out?" suggested Amy.
"Oh yes!" Sam was excited. "What shall we do?"
"Well, we need two types of soil and then we'll add some water and see how quickly it drips through." Amy told him.