Satellite Motion Satellite – a projectile moving fast enough to fall continually around the Earth rather than into it - the Earth surface drops a vertical distance of 5 meters for every 8000 meters traveled - this means that an object that you want to be a satellite around the Earth must be traveling at 8000 m/s

Circular Orbits A satellite in circular orbit around Earth is always moving perpendicular to gravity and parallel to Earth’s surface at constant speed Period – The time it takes for an object to make an complete cycle - the time it takes a satellite of the Earth to make a complete cycle or period is about 90 minutes

Circular Orbits Satellites orbiting the Earth are launched so that they are traveling at 8000 m/s This makes it so the satellite is traveling above the same part of the Earth at all times If the satellite is farther out from the Earth’s surface then it doesn’t have to travel as fast because gravitational force is not as strong

Elliptical Orbits A satellite in orbit around the Earth traces an oval-shaped path called an ellipse Ellipse – the closed path taken by a point that moves in such a way that the sum of its distances from two fixed points is constant Foci – the two fixed points in an ellipse

Elliptical Orbits When objects orbit the Earth in elliptical orbits they change speeds - the farther an object orbiting the Earth is from the Earth the slower it travels - the closer an object orbiting the Earth is to the Earth the faster it travels because gravitational pull is greater

Energy Conservation and Satellite Motion The sum of the kinetic energy and potential energy of a satellite is constant at all points along an orbit Apogee – the point in a satellite’s orbit farthest from the center of the Earth - the satellite travels slowest at that point Perigee – the point in a satellite’s orbits closest to the center of the Earth - the satellite travels fastest at that point

Kepler’s Laws of Planetary Motion Kepler’s First Law – the path of each planet around the sun is an ellipse with the sun at one focus Kepler’s Second Law – Each planet moves so that an imaginary line drawn from this sun to any planet sweeps out equal areas of space in equal intervals of time

Kepler’s Laws of Planetary Motion Kepler’s Third Law – the square of the orbital period of a planet is directly proportional to the cube of the average distance of the planet from the sun T 2 proportional to r 3 This means that the time it takes for a planet to revolve around the sun squared is equal to the average distance from the sun to the planet cubed

Escape Speed How fast does an object need to travel to escape the Earth’s gravity? km/s Escape Speed – the minimum speed necessary for an object to escape permanently from a gravitational field that holds it

Escape Speed in the Solar System Each body in the solar system has a different escape speed because the gravity of each body in the solar system is different