Because like the elbow, the knee is a hinge joint. It has a groove in it that keeps the movement in single plane. This makes the musculature required to articulate the joint simpler.
To move in more than one plane a joint needs either many bones in it (like the wrist), or has to be a ball and socket construction with muscles all round it to pull it in many directions (like the hip or shoulder).
Your mom can tell you that one
Hinge joints are found at the elbow and knee and they only allow movement in one direction or in only one plane.
the knee and elbow, hinge joints and only move on one plane (they can only flex and extend)
Many ships can move in any direction including backwards
Because they are joints that hinge. A hinge can only go one direction. Like for example, a door hinges, and it can only go one direction unless you break the door. Then the door could go anywhere, but hinges only move one direction.
Your neurons are adapted in such a way that impulses move only in one direction.
In a river or stream, the flow of water is in one direction only.
In a river or stream, the flow of water is in one direction only.
i think its the earthworm
On there first move they can skip one square They move only forward. They move in one direction normally and in a different direction to capture. If they reach the 8th rank they can be traded for another piece.
In One Direction
Imagine a shoulder that acted like you knee. It could only extend in one direction.