Steve L. Leydig, Age 10, Of Exeter, Calif., for his question:
Why do whirlpools turn opposite south of the equator?
Andy often gives only the first steps of a tough problem, and his readers can add the harder steps as they grow older. But eyen the first steps of this problem are hard for a young brain to grasp, and a simple answer would be wrong. So try your best and leave the rest until later.
North of the equator the whirling winds and waters tend to turn right. South of the equator they veer to the left. They must obey nature's traffic laws for all moving objects, and this problem is tough because two laws are at work. One sends a moving object in a straight path. The other bends its path right or left in the opposite hemispheres. This law is the coriolis effect, and it works because the earth spins toward the east.
The ground spins fastest at the equator, and the speed gets slower between the equator and the poles. At the equator it spins at 1000 miles an hour. Exeter is about 2500 miles from the equator, and here the ground spins eastward at only 850 miles an hour. An arrow starts out obeying the law that makes it take a straight path. But as it goes, the ground below is moving, maybe faster or slower or in a different direction.
If you shoot an arrow from exeter, the earth's spin of 850 miles an hour is included in its flight plans. Let's shoot it 2500 miles southward to the equator and pretend that its path is a long string. Along the way, the ground below spins faster and faster and the string lags behind. The string veers to the right and ends far to the west of where it started.
If you shoot the arrow northward, the ground below it spins slower. The path is bent to the right and it ends east of where it started. South of the equator, the ground spins faster below an arrow flying north and slower below an arrow flying south. Both paths are bent to the 1eft. This traffic law is the coriolis effect that spins the whirling winds and waters in opposite directions north and south of the equator.
Whirlpools may be changed somewhat by rocks and boulders. The winds above the earth are better examples of the Coriolis effect in action. A cyclone is a round whirlpool of winds blowing into the center. Their paths are like long strings above the spinning earth. The coriolis effect works to bend them day and night and soon they become whirling spirals. North of the equator they veer right and south of the equator they veer left, in the same direction as the hands of a clock.
The laws of moving objects were figured out by an English student named Isaac Newton. He was the genius who figured the laws of gravitation. But he did not explain why moving objects veer in opposite directions north and south of the equator. This was solved later by a French math genius named Gaspard Coriolis., and the hard to understand Coriolis effect was named in his honor.