Grades 3–5 · Organisms
Why can the room seem to move after you stop spinning?
After a playground turn ends, the ground can feel as if it is still moving. Your feet may have stopped while a message from deep inside your ears has not yet settled. The room itself has not started turning.
Inside each inner ear are curved, fluid-filled tubes called semicircular canals. They turn with your head. When a turn begins, the fluid initially lags behind the tube. This relative movement bends a soft structure containing tiny sensory hairs. Nerve messages tell the brain about the change in turning.
Starting and stopping a turn produce opposite relative fluid movements in an inner-ear canal.
During a steady turn, the fluid gradually catches up, so that turning message becomes smaller. When the head then stops, the fluid briefly keeps moving relative to the tube. The sensory structure bends in the opposite direction. The brain can receive a message that resembles a turn the other way.
Your eyes and feet supply other clues: the floor is still there, and your body is no longer turning. The brain has to combine these clues with the lingering inner-ear message. As the fluid and sensory structures settle, that temporary mismatch fades. The strange feeling reveals that sensing motion depends on moving parts inside us, not only on watching the world.
About this explanation
Schematic relationships are emphasized; sizes and timing are not to scale.
Starting knowledge: Recognize that forces can turn objects and senses send information.
Sources
- National Institutes of Health — Balance Disorders
- National Institute on Deafness and Other Communication Disorders — Balance