Water Absorption
Water Absorption is how a material soaks up and holds water inside it.
A dry kitchen sponge sits next to a bowl of water. When you press it in, tiny holes inside the sponge fill up with water. The sponge holds that water trapped in its gaps. This is how materials absorb water — they pull it into small spaces inside them.
Explaining water absorption by grade level
Some things soak up water and some do not. Put a drop of water on a piece of wood. The wood pulls the water in and feels damp. A plastic cup does not soak up water at all.
Projects that explore water absorption
Different types of wood soak up and hold moisture in different amounts. You cut identical blocks of redwood, teak, black oak, and red maple, then dry them in an oven at 100 degrees Celsius for 24 hours. After drying, you measure each block again with a caliper. The shrinkage happens mostly along the growth rings. Black oak soaks up and releases the most water, so it shrinks the most. Redwood absorbs and loses the least, so it shrinks the least.
A material's structure determines how much water it soaks up and holds inside it. You test six fabrics on a tilted ramp: cotton, silk, linen, wool, polyester, and nylon. You sprinkle 300 ml of water over each sample, then weigh it to measure how much water it absorbed. Cotton and linen soak up more water than polyester or nylon. You also repeat the test with samples coated in Scotch Guard, a water-repelling spray, to see how a coating changes how much water each fabric absorbs.