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Forces in our solar system

   Suppose we wanted to send a rocket into space.  The rocket would have to defeat two forces that are trying to keep it on Earth.  They are gravity and friction.  Gravity will pull the rocket back to Earth and friction will slow it down as it moves.  A rocket uses thrust to overcome these forces.  The rocket burns fuel to force gasses out one end.  Newton's law of physics states that for every action, there is an equal and opposite reaction.  By forcing gas out the rear, the rocket is propelled forward. It requires a tremendous amount of force in the form of thrust to overcome the Earth's gravity.  In fact, a rocket has to reach a speed of about 25,000 miles per hour to overcome it.  At this speed, the rocket could travel around the Earth  in slightly less than an hour. 

   Friction from air in the atmosphere is slowing the rocket down as leaves Earth.  In fact, heat from the friction would burn the rocket up if it weren't for heat shields (Tiles) on the spacecraft.  In fact, the shuttle Columbia burned up when it re-entered the Earth's atmosphere in 2003 when several of the tiles broke off during takeoff.  Since space is a vacuum, there is no friction in space and once an object is moving, it will stay at the same motion and speed for billions of years (Unless acted upon by another force.)

   Gravity also holds all the bodies in space in an orbit around the sun.  It also holds the atmosphere (Gasses surrounding a planet) on the planet.  Without these gasses we couldn't breath.  The gasses also retain heat.  Even though Mercury is the closest planet to the sun, we could not survive the extreme cold on the side of the planet facing away from the sun.  This is because Mercury does not have an atmosphere to retain heat (And it rotates very slowly so nights last a very long time.).

   An interesting feature regarding gravity in space is a black hole.  A black hole occurs when a massive star collapses in on itself.  The density (Thickness) becomes so tight that it creates so much gravity that nothing can escape its gravitational force.  This includes light. It is believed that there is a black hole in the center of all galaxies (Including our own, the Milky Way.)

   It is believed that an asteroid escaped Jupiter's gravity and crashed into Earth about 60 million years ago.  The kinetic force (energy ) from this event is said to have led to the extinction of the dinosaurs.  Kinetic energy is the energy we get from an object in motion.

   Fusion, or energy that comes when atom fuse, or combine, is what allows us to exist.  This is what drives the stars.  Our sun is using fusion to combine hydrogen and helium atoms together.  In this process, energy in the form of radiation (Which becomes heat and light) is released. It is this energy from the sun that provides us with heat, light, and food on Earth.



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