A Downhill Race
Bible Verse: Do you not know that those who run in a race all run, but one receives the prize? Run in such a way that you may obtain it. (1 Corinthians 9:24)
Materials Needed:
• Board, such as a table leaf
• Hollow cylinders (paper towel roll, empty soup can)
• Solid cylinders (dowel, thread spool, unopened can of food)
• Solid balls (golf ball, softball, rubber ball, marble)
• Hollow balls (tennis ball, racquetball, ping-pong ball)
Bible Lesson
The background of our key verse is the great athletic contests that were held during New Testament times. Corinth was where the Isthmian Games took place, a musical festival and athletic competition. The sports included wrestling, discus throwing, and running. This tradition continues today as the Olympic Games.
Most people enjoy competitive sports as either participants or observers. In a race there can be only one first-place winner. And to win, a runner must prepare well, as successful athletes in your audience will readily testify. The prize may only be a ribbon or trophy, but this token is overshadowed by the great honor of finishing first. In Paul’s day, the typical prize was a small pine wreath placed on the head of the winner.
Paul points out the great effort and sacrifice necessary to win a competitive prize. Yet far greater is the honor to be gained by being faithful to God. One can tell from the passage that Paul enjoyed sports, but he loved serving the Lord even more. How do we compare with Paul today?
Science Activity
Everyone likes a race, and you can provide one. The race down a sloping surface will be between four different objects: solid and hollow balls, and solid and hollow cylinders. The group might like to vote on which object will most likely win the downhill race. If the objects are similar in size and weight, the results are predetermined by physical laws of motion.
It may be difficult to have all four objects roll down the board at once. In this case the objects can be released two at a time, with the winner going on to the next round. To start a race fairly, hold the objects at the top, perhaps behind a ruler or yardstick. Then quickly raise the stick without pushing the spheres or cylinders. The race ends at the bottom of the slanted track.
A downhill race between different objects gives predictable results.
Science Explanation
Various objects falling through the air have similar motion if air resistance is small. So a stone, a book, or a pen all will hit the floor at nearly the same time.
A ramp race involves the rolling of objects, a more complicated process. Here the shape of the objects becomes important. Rolling motion is resisted by an object’s moment of inertia, given the symbol I. This I takes into account the size and distribution of matter within the object itself. Here are some moment of inertia values for several items, where R is the object’s radius and M is the object’s mass or heaviness:
| Object | I = Moment of Inertia | ||
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| Solid sphere | 2⁄5 MR2 | ||
| Solid cylinder or disk | ½ MR2 | ||
| Hollow sphere | ⅔ MR2 | ||
| Hollow cylinder or ring | MR2 | ||
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A solid sphere has the smallest I value, so it will roll the fastest. A hollow cylinder or ring has a large I value and generally lags behind the other shapes. The material that makes up a cylinder or ring is farther away from the rotation axis, and this slows the rolling motion. In contrast, the sphere has more of its mass close to the rotation axis and therefore it turns easily.