Planets are generally spherical because of gravity. The gravitational force created by a massive celestial body (a planet-sized body) attracts surrounding things towards its center. Gravity is relatively uniform on the surface of planets, and a sphere is the only three-dimensional shape where the exterior is equidistant from the center at all points. Bodies that are smaller, like a meteor or asteroid, are irregularly-shaped because they are not large enough to have a big gravitational pull.
Many of Earth’s (and other planets’) most astonishing features—the Grand Canyon, any beautiful river, and essentially all of the Earth’s landscapes—are due to weather and climate, which are affected greatly by gravity. Many other things are caused by the planet’s spherical shape, like how it feels to walk on the surface of the Earth, and the cycles of day and night.
What if the Earth were a different shape?
In this thought experiment, study how gravity,climate, tide,and organisms.
- Different Styrofoam shapes (sphere, cube, cylinder, pyramid, flat rectangle, etc.)
- Thin wooden dowels
- Desk lamp
- Camera or sketchbook and pencil
- Casserole dish
- Stick a wooden dowel through the center of each Styrofoam shape to serve as an axis.
- Turn on a desk lamp and bring your shapes about one foot away from the lamp.
- Turn each shape on its axis and note how to the light hits the shape. The lamp represents the sun. Observe how day (illuminated area) and night (shadowed area) is modeled on the different shapes. Rotate the shape on its axis. Which areas of the shape are lit? Are some areas always dark? Are some areas more brightly lit than others?
- One at a time, place each shape in a casserole dish and pour water from a cup over the surface. How does the water flow? Do some areas receive more water than others? Are some areas always dry?
- Observe each shape carefully. If gravity is always pulling towards the center of a body, which parts of the shapes’ surfaces would experience stronger gravity? Why?
Some shapes will experience different “days and nights” depending on how the axis is oriented. When pouring water to model ocean behavior, you should have observed that the water is not evenly distributed over the shapes. For a cube, gravity would feel “normal” on the faces, and it would be difficult to walk while on a corner, because gravity would be pulling down on either side of the cube, it would feel like walking on an incline.
Gravity is always pointing to the center of a body. This means the force felt by us on the face of the spherical planet Earth is the same on the entire surface. This is why it feels like we are always walking on a flat surface instead of a round one. With a differently shaped planet, points on the surface of the earth would not be a uniform distance away from the center. Walking on a flat face of a cubic planet would feel easy, and walking near a corner would be more difficult; as you were farther away from the center of the body, gravity would feel like it were pulling you down with more force.
Gravity also keeps the atmosphere and oceans on the Earth (instead of floating away into space), so having different forces of gravity would cause tidal waves, earthquakes, volcanoes, and other natural disasters more frequently. The atmosphere would be greatly affected. The air we breathe would make its way to the lowest points, which means that towards the corners of a cubic planet, it would be very difficult to breathe.
Were there areas of any of the shapes that were always in shadow? These areas would experience frigid, uninhabitable temperatures and would be in perpetual nighttime.
Water would not flow on the Earth in the same way if it were not spherical. Some areas would be far more affected than others, likely causing huge valleys and rifts at the points where the gravitational pull is the strongest. This would make the terrain difficult for animals to cross.
Based on what you’ve learned, make conclusions about what would happen if the Earth were other shapes!