What's the BIG Idea?: Amazing Science Questions for the Curious Kid
WHY DOES A ROLLING BALL STOP ROLLING
EVERYONE KNOWs A ROLLING BALL ALWAYS STOPS WHY ASK A QUESTION ABOUT SOMETHING EVERYONE KNOWs WHO CARES ABOT ROLLING BALLS ANYHOW UNLESS YOURE INTO BOWLING AS WHY DONT YOU Ask A REALLY DUMB A QUESTION LIKE WHY LE IS A RESTING BALL RESTING fornISH
4 What’s the Big Idea Four hundred years ago an Italian mathematician Galileo Ga-li-LAY-oh 1564 1642 did a thought experiment about this He concluded that rolling balls should never stop rolling That they do didn’t make sense to him Do Galileo’s thought experiment yourself use your imagination to see why Check it out Imagine how a ball rolls up a hill after you give it a little push It rolls slower and slower until it stops for a moment then rolls back downhill Now imagine how the ball rolls downhill It goes faster and faster Think about this If the ball rolling uphill slows down and the ball rolling downhill speeds up how should it roll if there is no hill A ball rolling on level ground should not speed up or slow down It should go at the same speed forever
WHY DOES A ROLLING BALL STOP ROLLING 5 But that’s not what happens in real life Balls rolling on level ground do come to a stop sooner or later Something must be stopping them What is it A hundred years after Galileo an Englishman named Isaac Newton 1643 1727 did some more thinking about this It’s obvious that a resting ball will rest forever It will remain resting until it is hit by some outside force that will make it move That’s easy to understand But Newton figured out that this same rule is true for balls that are already in motion Once a ball is moving it will keep on moving forever unless it is stopped by some force In other words just as a push or pull is needed to make resting objects start moving a push or pull is needed to make moving objects stop moving
