Spring Constant
Spring constant is a number that tells how stiff a spring is and how hard it pushes back.
Think of it this way
A stiff rubber band and a loose one show what spring constant means. Wrap a tight band around a stack of books — it barely stretches and snaps back hard. Wrap a loose band around the same stack — it stretches far with little force. The spring constant is that stiffness: a higher number means more push-back for the same stretch.
Explaining spring constant by grade level
Some springs are easy to squeeze. Some are really hard to squeeze. A stiff spring in a toy car pushes the car faster. A soft spring pushes it slower. The spring constant is just a way to say how stiff a spring is.