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Page 3 + ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com Happy/Sad Balls Investigation (continued) Part 2: 1. Have students brainstorm with their group. a. What would you like to know about the behavior of the spheres? b. How might you find the answers to your questions? 2. Have students write an "If, then" hypothesis statement to test a cause-and-effect relationship for their investigation. 3. Make sure they confirm the statement is testable by having the teacher check it. a. Ask students how they will measure the effect of changing their variable. For example: "We will measure the height of each ball's bounce before and after changing the independent variable." 4. Have students list the steps they plan to take during the investigation. 5. Set a timer for 15–20 minutes to complete their investigation. 6. Give each group a poster or large chart paper. Have them record the results of their investigation using pictures, charts, or graphs. Set a timer for 20–25 minutes. 7. Allow time for each group to share their results with the class. Expected Results: Results may vary based on materials used, setup, procedure, and other factors, however, here are a few examples on what to expect: • Movement on an inclined plain: Because of its lower coefficient of friction, the "happy" ball arrives at the bottom of the ramp or inclined plain first. The "sad/unhappy" ball rolls more slowly because of its much higher coefficient of friction, which makes this type of rubber ideal for racing car tires. • Density: The "sad/unhappy" ball is denser than the "happy" ball; it sinks in water, whereas the "happy" ball floats. • Energy Absorption Rate: If each ball is dropped from the same height onto a hard surface, the "happy" ball bounces, while the "sad/unhappy" ball does not (or very little). When the balls hit the hard surface, it is called a collision. There are two types of collisions, an elastic collision, and an inelastic collision. Elastic collisions conserve energy, if you drop a ball, it hits and makes a collision with the surface, and bounces back up to the same height. An inelastic collision is one in which some of the energy is lost during the collision. When dropped both balls are inelastic collisions because neither of them bounces back to its exact original position. However, the "sad/unhappy" ball is nearly perfectly inelastic. • Temperature: When the balls are cooled below room temperature the bounce of the "happy" ball is reduced, it does not bounce as high, the bounce of the "sad/unhappy" ball is increased slightly higher than it did at room temperature. Teaching Notes: Students will have different outcomes and learn different things from this investigation. The focus of the lesson is to encourage students to use scientific practices to plan and conduct descriptive, comparative and/or experimental investigations. Find materials for this activity at wardsci.com. Discover more free activities at wardsworld.com

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