Grades K–2 · Machines
How can a cart’s little wheel turn to follow it?
Some carts have little wheels called casters. Each wheel sits in a fork. The wheel can roll around its axle, and the whole fork can turn beneath the cart.
In the diagramOne wheel can turn in two waysSeen from above · the cart moves to the rightCart moves this wayWheel follows behind the jointTurning jointFork turnsFreelyWheel can rollThe fork can swing to follow a new direction.
The wheel sits a little behind the joint where the fork turns. As the cart changes direction, contact with the floor can swing the fork around. The wheel then trails behind its turning joint.
These two movements do different jobs. Rolling carries the cart along. Turning the fork helps the wheel follow a new direction. A fork that is held still cannot swing around this way.
About this explanation
Starting knowledge: Recognize rolling and turning.
Sources
- Blickle — Basic information and definitions