(Note: The seesaw for this activity may be constructed entirely with parts from hardware stores, or a carpenter-machinist might be helpful in its construction. Or, any seesaw can be used for the activity, as long as the LEGO MINDSTORMS NXT sensors can be attached to a moveable beam to demonstrate balance.)

The classroom seesaw set-up needs:

• 2 buckets or containers with large handles
• 1 2 x 4 wooden beam, 6 ft (2 m) long
• 2 2 x 4 wooden beam, 3 ft (1 m) long
• 2 2 x 4 wooden beam, 2 ft (0.6 m) long
• 4 wood screws, 2-3 in (5 cm – 8 cm) long
• metal rod, ¾ inch (2 cm) diameter
• 2 rubber bands
• 1 elastic (bungee) cord
• 1 ball bearing (same inner diameter as metal rod)
• LEGO MINDSTORMS NXT robot, such as the NXT Base Set (5003402) for $159.98 at https://shop.education.lego.com/legoed/en-US/catalog/product.jsp?productId=5003402&   isSimpleSearch=false&ProductLine=NXT
• LEGO MINDSTORMS Education NXT Software 2.1, available as a single license (2000080) for $39.97 or a site license (5003413) for $271.96 at https://shop.education.lego.com/legoed/en-US/catalog/product.jsp?productId=prod120017&isSimpleSearch=false&ProductLine=LEGO+MINDSTORMS+Education+NXT
• computer, loaded with NXT 2.1 software

• multiple objects of the same weight and size, to use as weights (such as bulk packages of water bottles or sandwich bags filled with sand) (Note: Water bottles of 11 fluid ounces [325 ml] were used successfully with the set-up described in this activity, and as much as 24 bottles were used on each side without functionality problems. However, heavier objects may work.)
• several plastic bags or containers for the objects

Note that single licenses and site licenses are available; site licenses may make sense for schools with high use.