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THINKS ABOUT IT What is a satellite? VIDEO SATELLITE Any object that orbits another object in space Our moon is a natural satellite Artificial satellites are launched into orbit Used for communications, military intelligence, weather analysis and geographical surveys The ISS (International Space Station) is an example of an artificial satellite CIRCULAR MOTION Artificial satellites travel around Earth in almost circular path An object moving in a circular path is accelerating because it is constantly changing direction If an object is accelerating, a force must be acting on it – called centripetal force Centripetal means center seeking The Earth’s gravity is the centripetal force for the satellite. It keeps pulling the satellite towards the Earth SATELLITE MOTION Q: Why don’t satellites fall to Earth like a thrown ball does? A: They have a greater horizontal velocity than a ball thrown on Earth EXPLANATION: A ball thrown has horizontal force moving it forward. Gravity is a force acting to pull it to the ground. The more force you give the ball the faster it travels horizontally and the greater distance it travels before hitting the Earth A satellite in orbit around the Earth is continuously falling towards the Earth, but because the Earth is curved and they are traveling so fast , they don’t hit but travel around it A satellite is a falling projectile that keeps missing the ground!! SATELLITE MOTION A satellite does not need fuel because it continues to move ahead due to its inertia Gravity continuously changes its direction The speed required to keep a satellite in orbit is 7,900m/s IF THE MOON IS ATTRACTED TO EARTH BY THE FORCE OF GRAVITY, WHY DOESN’T THE MOON CRASH INTO EARTH? •Inertia - an object's resistance in speed or direction until an outside force acts on the object. In space, there isn't any air to cause resistance and slow down the moving moon. Therefore, the moon continues to move, but gravity keeps the moon in orbit. Click on the picture to learn more about the motion of the moon. SATELLITE LOCATION Mapping and observation satellites are put into low orbits of less than 1,000 km Completes an orbit in less than 2 hours Satellites such as communications satellites put into higher orbits (36,000 km) where they circle the Earth in 24 hours Because of this they remain over the same point on Earth – Geosynchronous orbit PUTTING UNIVERSE & WEATHER TOGETHER Every planet that has an atmosphere has weather. Jupiter’s Great Red Spot appears to be very similar to a hurricane system on Earth, but it has lasted for centuries, driven by the planet’s internal thermal energy. Write a humorous but accurate weather forecast for one of the outer planets that has an atmosphere. Remember to include temperature, wind speed and direction, barometric pressure, dew point, relative humidity and cloud description.