What happens to a jar of big and little balls when you shake it?
Look at this jar… big balls and little balls, all jumbled up together. Now we get to shake it, hard! Shaking usually mixes things up even more, right? Let's see. Ready to guess… will the balls MIX up, or SPLIT into stripes?
After you watchWhat happens to a jar of big and little balls when you shake it?
The short answer
When you shake a jar of big and little balls, it splits into stripes instead of mixing. Each shake opens tiny holes between the balls. Only the little balls are small enough to sneak down through those holes, so the little ones sink to the bottom and the big ones get pushed to the top.
Try this next
- What if all the balls were the same size? Picture a jar where every ball is the same. Guess first, then think it through: with no little balls to sneak through holes, will it split into stripes or just stay mixed?
- What if you only shook it one little time? Guess how many shakes it takes before you can spot a stripe. Then imagine shaking once, twice, three times, and watch the little balls trickle a tiny bit lower each shake.
The whole story
How it works
Shaking makes the whole pile jiggle and lift for a tiny moment, and little holes open up between the balls. The little balls fit through those holes and trickle down, but the big balls are too fat to fit, so they get nudged up. After lots of shakes the jar has little balls in a stripe at the bottom and big balls in a stripe on top.
What people get wrong
Kids think shaking always mixes things up more. But when a jar has big and little balls, shaking does the opposite — it sorts them into stripes, because the little ones keep sneaking down through holes the big ones can't fit through.
The catch
Sorting by shaking is handy — it's how machines line things up by size, and why cereal settles neatly in the box. The catch is the big pieces always crowd the top and the crumbs sink, so the last bowl is never like the first. Same-size balls stay nicely mixed, but then shaking can never sort them when you want it to.
Questions kids ask
Why do the big balls go to the top, not the bottom?
Because they are too big to fit through the little holes. The little balls keep sneaking down through the holes, and as they pile up at the bottom they push the big balls up to the top.
Does shaking ever just mix things?
Yes — when all the balls are the same size. Then no ball is small enough to sneak past the others, so shaking just jumbles them and they stay mixed.
Do the little balls sink because they are heavier?
No, it's about size, not weight. The little balls sink because they fit through the tiny holes the big balls leave. Even light little balls slip down past big ones.
Talk about it
- Before we shake the cereal box, guess: which pieces end up on top, the big ones or the crumbs?
- If the little pieces sink, does that mean they're the heaviest? What else could let them slip down?
- Where else have you seen big things end up on top — a bag of mixed nuts, a snack box, a bucket of toys?
For grown-ups
This is granular size segregation, famous as the Brazil-nut effect. Vibrating a mix of grains makes the bed loosen a little each shake; small grains percolate into the gaps that open beneath larger ones, while convection rolls carry the big ones up and trap them on top. So shaking can un-mix a mixture instead of mixing it.
Keep going
What else makes you wonder?
- What if you shook the jar sideways instead of up and down?
- What happens at home when you shake a box of cereal or a bag of trail mix?
- Could you ever shake the jar so the big balls go to the bottom instead?