Imagine how far you could kick a soccer ball if gravity didn't pull it toward the ground. On Earth we take gravity for granted -- especially when it comes to playing sports. When we shoot a basketball, we expect it to go down toward the ground after it goes through the hoop. If we turn a cartwheel, we know that we will land shortly in a place near our starting point. Most sports involve keeping our feet on the ground most of the time. The constant force of gravity on Earth gives us different results than we would get if we played sports in space.
Gravity is present on the International Space Station, but astronauts orbiting Earth experience "microgravity." The prefix "micro" comes directly from the Greek "micros," which means "small." The pull of gravity seems very small compared to what astronauts feel on Earth. The reason is because everything on the orbiting station is in a state of free fall. The station and everything inside it are constantly falling toward Earth. So, if an astronaut drops something, it does not fall to the floor because the floor is falling, too. Everything seems to float.
Microgravity isn't the only factor that changes the game in space. Consider Newton's Laws of Motion, which describe relationships between motion, matter and force.
| Law | Also known as ... | Description |
| First law of motion | Law of inertia | An object that is not moving will not move until a force makes it move.
An object that is moving will continue to move at a constant speed and direction until a force causes it to change. |
| Second law of motion | F=ma | The force of an object equals its mass times its acceleration. |
| Third law of motion | Law of action and reaction | For every action there is an equal and opposite reaction. |
We're used to the way Newton's laws work on Earth under the force of gravity. Newton's laws also apply in microgravity, and sometimes it's easier to see how they work when you watch demonstrations on the space station. You can actually see an object at rest suspended in the air until a force causes it to move. In the DIY Podcast Sports Demo video, one of the ways astronaut Clayton Anderson demonstrates Newton's laws is by swinging a bat to hit a baseball floating in midair.
The laws of aerodynamics are another set of physical laws that apply to sports. Aerodynamics is the study of the way objects move through air. You can see the effects of these laws as you watch the trajectory of a ball. The laws of aerodynamics come into play when we set guidelines and rules for a sport -- such as the three-point line in basketball or the yard line for a football kickoff.
Another scientific principle that may be easier to understand once you see Anderson demonstrate it in space is the conservation of angular momentum. This law says an object will spin more slowly as resistance increases. An object will spin faster as resistance decreases. An example of angular momentum is a spinning ice skater. When skaters tuck their arms in tightly (decreasing the moment of inertia), rotational speed increases. But, when skaters extend their arms (increasing the moment of inertia), the speed at which the skaters spin slows. On the space station, it is easy to show the conservation of angular momentum while tumbling through the air. Don't try that on Earth!
Even though the same scientific laws and principles apply on Earth and the space station, it's fun to see them demonstrated in microgravity -- especially with the same sports we play on Earth.
More about Sports and Microgravity > NASA -- What is Microgravity? > The X-Moon → > Moon Tennis > Aerodynamics of Baseball → > Forces on a Baseball → > Return to Do-It-Yourself Podcast Main Page
