• spring scales, preferably having a 500 g capacity and 5-10 g accuracy, one per team of 2 to 4 students; Ohaus makes one that works well for this exercise; it is available from suppliers such as Ward for about $6
• ceramic coffee mugs, one per team, have students bring these from home or purchase them from thrift stores
• scissors, one per team
• roll of masking or wide transparent tape per team, or one roll shared between two teams
• string, about 30 cm per team
• several beakers, yogurt containers or paper cups filled with pebbles, nails or pennies; one container per team; these relatively heavy materials provide "ballast" to offset any weight differences in the bottom surfaces attached to the sliding objects
• (optional) lubricating materials, such as household oil like WD40™, vegetable oil, waxed paper, talcum powder, graphite powder, liquid and/or bar soap; make these available if students are curious about lubricants, as described in the Activity Extensions section

Vary the bottom surfaces of the coffee mugs by making several "plates" out of differently-textured materials, and taping these plates to the undersides of the mugs. Cut the materials into circular or square pieces slightly larger than the mug bottoms. Example materials to make these interchangeable bottom surfaces:

• poster board and/or cardboard
• stiff glossy paper, such as from a folder or catalog cover
• glass, from an art supply store or as scraps from a window repair company
• carpet, linoleum and/or ceramic tiles, ask for samples or scraps from a flooring company
• thin plywood or balsa wood, ask for scraps from a building supply store or hobby shop
• metal, such as jar lids
• plastic, such as margarine tub lids or laminated cardboard
• Styrofoam™, cut from the bottom of a disposable picnic plate
• sandpaper glued to heavy cardboard

Choose these materials so they are as flat, clean and free of gouges and scratches as possible.