Explain Weightlessness
When can you feel weightless? There are two basic ways. You can be far enough away from all large objects in the universe that the force of gravity due to them cannot be felt. Or you can be in free fall.
One form of free fall keeps amusement parks in business. When you are falling toward the Earth with an acceleration of 9.8m/s2, you feel weightless. No force pushes you onto your seat and your stomach seems to have moved north to make friends with your heart and lungs. The most current rage is the drop type rides. If you position a penny on your knee at the top of the ride previous to they drop you, you can observe if there is any force left to hold the penny on your knee, if not, then the penny will "float" up as you fall, and you can prove that you really were in free fall.
In this case, free fall is when the force of gravity is busy accelerating you and there is no force left over to keep you pushed into your seat. There are also times on roller coasters that you may be in free fall. While you crest a hill and start down, you maight feel weightless, and while you reach the bottom and start back up, you may feel extra force pushing you into your seat. At the bottom, you comprise the conflicting of free fall, your motion in fact adds to the force of your weight and you are pulling "g"s and being pushed into your seat harder.
Another situation in which you can feel weightless is when you are on a relatively small object like the space shuttle orbiting the Earth or any other planet or star. While the shuttle orbits the Earth, the force of gravity is busy keeping you and the shuttle in orbit, there is no force left over to push you towards any particular side of the space ship, so you just float.