Objects in Orbit Monday, January 30, 2023 Core: State why objects orbit others and describe the uses of satellites. Extension: Investigate and describe the relationship between gravitational pull, orbit speed, shape and length. Challenge: Explain how orbits exhibit conservation of energy. Key terms: elliptical/circular orbit, gravitational attraction, gravity, satellite and geostationary. Starter: What causes orbits? Objects in Orbit • Earth’s orbit of the sun is almost circular. • Most of the other planets, dwarf planets and comets orbit the sun on orbits that are ellipses or slightly squashed circles. • The sun is not ‘at the center’ of these technically as the orbit is not circular, but it is what they orbit around. • But what keeps these objects in orbit? • Gravity provides the force needed to maintain stable orbit of planets around a star and also of moons and artificial satellites around a planet. Weight, Mass and Gravitational Field Strength • Gravity is the force that exists between any two objects with mass. • The more massive the object, the larger its gravitational pull and therefore field strength. • The sun contains 99.9% of our solar systems mass, this is why so many objects orbit it, as it has a very strong gravitational pull. • When in orbit the force of gravity acts towards the centre of the orbit. • The direction of motion (i.e. the velocity) of the object is always at right angles to the direction of force. • Without this force, planets would just continue to move in a straight line. • They must maintain the same speed to stay in orbit. Task 1: Investigating orbit size and Speed 15 minutes Follow the instructions on the selected worksheet. Extension: Can you relate your observations to the Sun’s gravitational field strength? Task 1: Investigating orbit size and Speed Conclusions • As the length of the string decreases, the time taken to orbit decreases and orbital speed increases. • A planet's orbital speed changes, depending on how far it is from the Sun. The closer a planet is to the Sun, the stronger the Sun's gravitational pull on it, and the faster the planet moves. • The farther it is from the Sun, the weaker the Sun's gravitational pull, and the slower it moves in its orbit Gravitational Pull, Speed and Orbits • Do you think this would be the case for objects like comets with elliptical orbits? • Objects with a circular orbit maintain the same speed as they experience the same gravitational pull throughout their orbit. • Objects with an elliptical orbit change speed. When they’re closer to the sun they speed up and the further away they are, the slower they move. As the comet moves away from the sun, the force of gravity reduces its speed, reducing its kinetic energy and increasing its potential energy. As the comet approaches the sun, the force of gravity on the comet increases its speed, increasing its kinetic energy and reducing its potential energy. This means at any point in the comet’s orbit, its total energy remains constant. Task 2: Question Check 5 minutes Task 2: Question Check-Answers 1. ai) Gravitational attraction between the sun and the planets. 1. aii) Venus is closer to the sun, so experiences a greater gravitational pull, therefore travels at a higher speed, so has a shorter orbital time. Task 2: Question CheckAnswers 1. bi) D 1. bii) B 1. c) orbit in the same direction as Earth’s orbit. 1. ci) ellipse 1. cii) gravity • Satellites in a circular orbit around Earth, move at a constant height above its surface. • To stay in a stable orbit, the satellite needs to move at a particular speed. Satellites • This needs to be considered when launching satellites, too fast and it will fly off into space, too slow and it will fall back down to Earth. Types of Satellites- Communications • Communications satellites are responsible for radio, tv and other signals from one part of Earth to another. • They orbit the Earth, every 24 hours in the same direction as Earth’s spin. • So, they stay above the same position on Earth’s surface as they go around it. • We refer to them as… Geostationary Types of Satellites-Navigational • Navigational satellites are used by different modes of transport to locate their position. • Global positioning systems (GPS) use them to calculate positions. • To do this a receiver on Earth picks up signals from different satellites, compares arrival times and uses it to calculate positions. Types of Satellites-Monitoring • Monitoring satellites such as weather satellites contain cameras and other detectors. • They have very low orbits compared to geostationary satellites and scan the whole Earth. • They also have much shorter orbits, orbiting the Earth every few hours. Plenary: Exam Questions Objects in Orbit Monday, January 30, 2023 Core: State why objects orbit others and describe the uses of satellites. Extension: Investigate and describe the relationship between gravitational pull, orbit speed, shape and length. Challenge: Explain how orbits exhibit conservation of energy. Key terms: elliptical/circular orbit, gravitational attraction, gravity, satellite and geostationary.
