Did Luno Find His Brother?
3 Minutes
Rolling and sliding objects for kids: learn why shapes roll, slide, or do both with Bruno and Mr. Banana Tree. An English science lesson.
- Finding the deep tree and asking Mr. Banana Tree for help
- Why round shapes roll and flat shapes slide
- Testing watermelons, bricks, coins, balls, and plates
What this lesson teaches
Objects move across surfaces by rolling, sliding, or performing both actions depending entirely on their shape. A round or circular shape allows an object to roll smoothly, while a flat and non-round shape causes an object to slide.
How shape determines movement
Objects can be separated into three distinct categories based on their movement: objects that roll, objects that slide, and objects that can do both. The most important physical feature common to all rolling objects is a round or circular shape. When an object does not have this round quality, it cannot roll forward and must slide across the surface instead. Observing the shape of an object is the easiest way to predict how it will move.
Objects that only roll or only slide
- A watermelon is in a perfectly round shape no matter how you look at it, so it will only roll.
- A ball is round in every direction, meaning it can only move by rolling across the floor.
- A heavy brick has no round shape whatsoever, so it will only slide along the ground.
Objects that can both roll and slide
- A flat plate easily slides across a surface because of its flat structure.
- That same plate also forms a perfect circle shape, which allows it to roll along its curved edge.
- A coin can slide along the ground on its flat faces, but its round outline allows it to roll as well.
- Objects with both a flat body and a circular boundary can either roll or slide depending on how they are placed.
Rules for identifying motion
Determining whether an item will roll, slide, or do both requires paying attention to all sides of its shape. When an object is completely round like a ball or a watermelon, it only rolls because it lacks flat surfaces. When an object is entirely non-round like a brick, it only slides because it cannot turn over itself smoothly. Any object that shares both a flat face and a circular edge can perform both movements.