we teach kids "stuff" that they really don't believe ... like the earth is round.

Piagetian ideas blossom in this interesting article

the earth is round? who are you kidding?

alan lightmand / philip sadler: s/c feb 88

one of the first scientific facts we announce to our children is that Earth is round. That flat, flat ground we walk, ride, and play on, stretching endless miles in perfect and reliable flatness, actually wraps around on itself to form a giant ball. Preposterous, yet a scientific fact. For proof, look at the globe in the classroom or the photos of Earth from space.

if we expect young children to believe this story, we're wrong.

Studies done in the USA and Israel indicate that as late as the fourth grade almost half the children believe Earth is flat. Most of the remaining fourth grader who say, "The Earth is a round ball," actually picture a flat part where people life in the interior of the ball. Other draw Earth as a giant pancake or as a curved sky covering a flat ground. These findings run head on against teachers' and parents' perceptions of what their children have learned.

we asked 65 elementary and middle school teachers to predict how their students would draw the Earth. The teachers greatly overestimated their students' knowledge. For instance, 2nd grade teachers believed that 95% of their students knew Earth was round when less than 5% of them actually did. clearly, our children are struggling with a contradiction between what they are told about their world and what they see with their own eyes. Such a struggle will inevitably be repeated in other science topics: The world is not always as it seems. The concept of a round Earth presents one of the earliest and most striking examples of this critical lesson in science.

what looks flat might be round the biggest obstacle to accepting a round Earth is that it indeed appears flat. To attack this obstacle, we have to show children that something can look flat even when it obviously is not.

in the last year, we have developed and given classroom demonstrations to local first graders using a very large balloon and a toy ship. The demonstration gives young children an intuitive feeling for the shape of Earth.

we inflate the balloon and have each child, one by one, place her cheek against the balloon, closing the outer eye and looking with the inner eye out over the surface of the balloon. We ask the child to then describe what she sees to the class. Does the horizon look round or flat?

if the balloon is large enuff, the surface looks flat and the child says so. We then emphasize to the class that when a person is very close to a large object, it always looks flat. The object might be shaped like a board or a ball or a cigar, but it will always look flat for very close up. In the present case, the child can see that the balloon is round when they are sitting far away from it -- just as astronauts can see Earth's round from high above it. But when we are sufficiently close to the balloon or Earth, it appears flat.

ideally, the balloon used for the demonstration should be l0 ft or more in diameter. We used a l2 ft diameter latex weather balloon purchased at a surplus store for about $20. It can be inflated in five minutes by reattaching a vacuum cleaner's hose to the exhaust. We inflated it to about l0 ft to avoid the tension and possible popping at its peak capacity.

the children should definitely watch as the balloon is inflated. They become enormously excited as this small piece of rubber gets larger and larger, eventually filling up much of the room and forcing them farther and farther back toward the walls of the room. Once inflate, the opening nozzle of the balloon may be either tied off or held closed by one of the students during the demonstration.

a ship on the horizon

students should now realize that appearances can be deceptive. Earth is not necessarily flat just because it looks flat. However, this realization still leaves open what the true shape it might be. It could still be flat, & to find out, we need more information.

a second demonstration with the balloon helps. Again, with the child's cheek against the balloon and with her eye closest to the balloon looking at its horizon, we slowly move a toy ship across the surface of the balloon toward the child. As we do this, we ask her to describe what she sees.

at first, when the ship is on the opposite side of the balloon from the child, she will see nothing. When the ship first appears on the balloon's horizon, the child will see only the uppermost part of the ship. As the ship travels closer to her, she will report seeing more and more of the lower parts of the ship. Finally, the ship will be in full view for her. On clear days, this is exactly how sailors see distant ships ... little by little from the top of the mast down. Ptolemy, the famous astronomer, cited this observation as evidence of Earth's roundness.

now the class will be talking about the curved surface of the balloon as the curved surface of Earth. But the experiment isn't over.

using the flat surface of a large table instead of the balloon, we repeat the demonstration with the toy ship. The child reports seeing the entire ship at once ... and we emphasize the difference between the observations.

naive theories and young minds
childrens' deep-seated impressions that Earth is flat is preconceived notion, or what science educators call a naive theory. Such theories, based on common sense experiences from an early age, are difficult to give up and can strongly interfere with any learnings that challenge them.

many students have trouble believing that in a vacuum, a cannon ball and a feather dropped from a tree would fall at the same speed. In a world of experience, air resistance generally causes heavier objects to fall faster. Even scientists can make mistakes by placing too much trust in their personal experiences. Science educators have only recently begun to realize the importance of confronting naive theories and helping students examine their beliefs about the world. Such an examination can begin very early in a child's education. ( see references in article )