Something moves. A force must have been involved. Forces push, pull, press, stretch, and turn objects. They vary in size, strength, and direction.

Sometimes, when a force acts on an object that can move, the object will move in the same direction as the force. If forces act on objects that cannot move, the objects may change shape or break apart.

One fundamental force is gravity. On Earth, gravity is the force that keeps us on the ground. We feel the Earth’s gravity pulling us towards the Earth.

The Space Shuttle and Space Station orbit around the Earth. The Earth's gravitational pull is what keeps the Space Station from zooming off into space. Inside the Space Shuttle and Space Station, objects seem to float as if they are weightless. In this reduced environment, things float because everything is falling at the same rate.

Floating food, drifting sleeping bags, and a hammer floating across the room are all part of life in a reduced gravity environment. Astronauts work in these conditions while traveling in space.

Astronauts in orbit can often move huge, heavy objects with just the slightest effort.

Reduced gravity also affects the human body. The heart doesn't beat as fast. Your bones lose needed calcium.

Most of these effects on the body are reversed after astronauts return to Earth. They may feel weak and lose their balance at first, but they usually recover in about one week.

KSNN thanks NASAexplores as a source of information. Visit NASAexplores. For more information about this topic and additional teaching resources go to (http://www.nasaexplores.com).