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The magnetic force can keep an object suspended on the side of your metal appliances for eternity. Even stronger magnets, using superconductors, can levitate entire train cars, enabling super-fast transportation that floats above the track.
Gravity, also called gravitation, in mechanics, the universal force of attraction acting between all matter. It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter. On the other hand, through its long reach and universal action, it controls the trajectories of bodies in the solar system and elsewhere in the universe and the structures and evolution of stars, galaxies, and the whole cosmos. On Earth all bodies have a weight, or downward force of gravity, proportional to their mass, which Earth’s mass exerts on them. Gravity is measured by the acceleration that it gives to freely falling objects. At Earth’s surface the acceleration of gravity is about 9.8 meters (32 feet) per second per second. Thus, for every second an object is in free fall, its speed increases by about 9.8 meters per second. At the surface of the Moon the acceleration of a freely falling body is about 1.6 meters per second per second.
Going further, it’s not all that difficult to defy gravity and get into space. After all, the edge of space is just 62 miles (100 kilometers) away and shooting something straight up for that distance is not the hardest thing to do in the world.
But gravity does have a superpower. Even at the edge of the atmosphere and the beginnings of space, Earth’s gravitational pull is not much weaker than what it is on the surface. So, unless you keep accelerating, eventually gravity will pull you back.
Most of the energy that we put into rockets does not go into getting to space, it goes into staying in space. If you want to escape the gravitational clutches of the Earth altogether, you must achieve a speed of at least 25,000 mph (15,570 km/h), which is around 33 times the speed of sound.
Once in space, we have some methods available to simulate the effects of gravity. This is important because a constant gravitational pull is vitally important for maintaining healthy bodies. Without gravity, our hearts grow weaker, our bones get thinner, and our entire cardiovascular system diminishes. Without constant exercise, astronauts who spend too much time in zero-G couldn’t survive a return to Earth.
Speaking of science fiction, writers and authors love to come up with all sorts of gravity-defying gizmos, whether to provide artificial gravity for their ships or to propel their spacecraft through the universe. Unfortunately, it seems that these kinds of anti-gravity devices will remain in the realm of fiction.
To operate these devices, it would require the use of negative matter, which is a form of matter with negative mass (not to be confused with antimatter, which is like normal matter but with opposite charge). We have never observed negative matter in the universe, and we strongly suspect it can never exist, because it would violate our understanding of the conservation of momentum, which is a big deal.
However, at the largest scales in space, we already observe an anti-gravity effect. We have known since the observations of Edwin Hubble, about a hundred years ago, that our universe is expanding – over time, the average distance between galaxies grows. But in the late 1990s, two independent teams of astronomers discovered something remarkable: Not only is the universe expanding, but that expansion is accelerating. The universe is expanding faster and faster every single day.
The name we give to this phenomenon is dark energy, and it appears to be an anti-gravity force that is repelling all the matter in the universe. Anti-gravity is not all that strange in Einstein’s general theory of relativity, which is the set of equations we use to understand how gravity works. In general relativity, any kind of tension, like the tension in a stretched rubber band, creates an anti-gravity effect. But usually, this anti-gravity effect is completely swamped by the normal, attractive gravity that we are used to.
Satellites can orbit around the planet because they are locked into speeds that are fast enough to defeat the downward pull of gravity. Satellites are sent into space by a rocket launched from the ground with enough energy (at least 25,039 mph!) to get outside our atmosphere. Once the rocket reaches its determined location it drops the satellite into its orbit. The initial speed of the satellite maintained as it detaches from the launch vehicle is enough to keep a satellite on orbit for hundreds of years.
A satellite maintains its orbit by balancing two factors: its velocity (the speed it takes to travel in a straight line) and the gravitational pull that Earth has on it. A satellite orbiting closer to the Earth requires more velocity to resist the stronger gravitational pull.
Satellites do carry their own fuel supply, but unlike how a car uses gas, it is not needed to maintain speed for orbit. It is reserved for changing orbit or avoiding collision with debris.
