Children can use scrub brushes to explore the concept of abrasion, the fine wear caused when two objects rub against each other. These experiments all take the basic form of rubbing a scrub brush against an object and counting the number of scratches (or scratches per unit width) that are formed. The independent variable can be the pressure or speed with which you brush, the number of strokes, the type of brush or the material being brushed.
This experiment tests the efficacy of different cleaning solutions. Begin by baking a batch of cookies on an ungreased baking sheet to create dirty patches as that are as nearly identical to each other as possible. On each dirty patch, use an eye dropper to apply one drop of a different cleaning solution, such as dish soap, hand soap, bleach or window cleaner. Brush each spot in a standardized manner, such as 10 brisk strokes with the handle of the brush 2 inches above the baking sheet. Observe the patches to see which product removed the most cookie residue.
A friction race is like the opposite of a model car race. Each contestant creates a "race car" by attaching a weight to the top of a scrub brush. Define a maximum weight that the race cars may not exceed. Create a race track by leaning a board against a wall or chair to create an angled ramp. The board may be wide enough for all of the race cars to run at once or contestants may take turns on a narrower board. Use different scrub brushes and different weights to try to achieve the slowest run down the ramp.
This experiment uses scrub brushes to help test the rate at which cardboard breaks down when soaking in water. Cut a large piece of cardboard into identical rectangles about 6 inches by 12 inches apiece. Submerge each piece in water for a different amount of time, such as 30-second or 2-minute increments. When each piece is done soaking, remove it from the water and see how many strokes it takes a scrub brush to wear through the cardboard to form a visible hole. Make sure to standardize the size, direction and pressure of the brush strokes.