What is Stiffness?

Stiffness is how much something resists being bent or squished when you push or pull it.

Imagine you're playing with a toothbrush and a rubber band. If you press on the toothbrush, it doesn't change shape much, that’s because it's stiff. But if you press on the rubber band, it easily stretches and bends, that’s because it's not stiff, or more flexible.

Think of a plastic spoon and a sock. The spoon is hard and doesn’t bend much when you twist it, that’s stiffness. A sock is soft and squishy, so it bends easily, that's less stiffness.

When something is stiff, like your chair, it stays the same shape even when you sit on it. But if it were soft like a pillow, it would sink in and change shape.

Stiffness is just how much something fights back when you try to make it move or change shape, like a toothbrush fighting back when you press on it!