Workshops: Skimmer Regatta 5
Mass and Balance
Students decide whether adding pennies will stabilize the skimmer or merely slow it down.
SCIENCE BACKGROUND CAPSULE
Mass is the amount of material an object is made up of. Weight is a measure of the pull of the force of gravity on the mass. On Earth, weight and mass are essentially the same. Every object has a point on which it can be held in balance. This balancing point is called the object's center of gravity. In general, the lower and object's center of gravity, the more stable the object is. Therefore, adding mass to the base of an object around the balancing point make the object more stable. However, adding mass unevenly to an object can change the object's center of gravity and make the object less stable. If a significant mass is free to move around on a moving object, the object's center of gravity keeps changing and can make the object unstable and interfere with forward motion. In Explore, students add mass in the form of marbles to a milk carton to make it more stable. Students also find the balancing point of a ruler with equal and unequal mass at the ends.
In Investigate, students apply what they've learned about balance and adding mass for stability to the skimmer. Students will experiment to decide if adding pennies affects the skimmer's stability and the distance it travels. Two pennies may add stability and make the skimmer move straight but decrease the distance the skimmer travels. Results will vary from skimmer to skimmer because of various weight and size of sails, etc.
Have students complete Steps 1-5 of the Explore activity in their teams. Be sure students find the ruler's balancing point before they add pennies.
Have a student read Challenge! aloud. Tell students they have two minutes to work on the Challenge! activity. After two minutes call an all-class Think Tank meeting.
THINK TANK MEETING
Ask a few students to describe how a teeter-totter works. Guide them to say that it works best when the two people are the same weight. Discuss what happens when people of different weight play on a teeter-totter. [Heavier person stays on the ground.] To make the teeter-totter work, the heavier person must move closer to its center. Therefore, changing the distance between the balancing point and the heavier child (heavier load) can also balance a teeter-totter.
Circulate to check on teams' progress. Since this is the last card before the Regatta, you may want to provide each team with a Design Choice Record summary form that has them state all their final choices.