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14/05/2017 Gravity and Space Gravity 14/05/2017 Gravity is an attractive force that affects anything with mass: Note that this force goes both ways – the Earth is attracted to us. Gravity Gravity depends on 2 things: 1) The mass of the objects F If you double the mass of one object you double the force 2F 2) The distance between them If you double the distance the gravitational force divides by 4… F F/4 14/05/2017 Weight vs. Mass 14/05/2017 Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. W Weight = Mass x Gravitational Field Strength (in N) (in kg) (in N/kg) M g 1) What is the weight on Earth of a book with mass 2kg? 2) What is the weight on Earth of an apple with mass 100g? 3) Dave weighs 700N. What is his mass? 4) On the moon the gravitational field strength is 1.6N/kg. What will Dave weigh if he stands on the moon? Rockets When a rocket flies away from Earth the force needed to keep it accelerating decreases: 14/05/2017 _____ force needed here _____ force needed here This is because… 1) As the rocket gets further away from Earth the force of ______ decreases. 2) As the rocket burns fuel it gets _______, also decreasing the gravity downwards. Words – gravity, smaller, large, lighter Natural Satellites Mercury Venus 14/05/2017 These planets are all satellites of the sun Earth Mars Jupiter Saturn Uranus Neptune Pluto Artificial Satellites 14/05/2017 Artificial satellites have been around for 50 years and have 3 main uses: 1) Observation (e.g. Hubble Space Telescope) – these are in orbit high above the Earth and can observe the universe without interference by the ____________ 2) Communications (e.g. ___, phone, car “SatNav” systems) – these satellites are in “geostationary” orbits. This means that the satellite always stays above ____ ____ point on the Earth and takes a ______ to complete an orbit 3) Monitoring (e.g. weather, spy satellites) – these satellites have a “___ _____” orbit and may scan around the Earth several times a day Words – the same, atmosphere, low polar, TV, day
