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UNIT 9J Gravity and Space LEARNING OUTCOME • Explain the difference between mass and weight • Describe gravity Weight and Mass Weight and mass are not the same. Mass is the amount of matter in an object. This will have the same value anywhere in the Universe including space. Weight is a force and it is caused by the pull of gravity. In fact, weight is the pull of gravity acting on a mass. Weight and Mass Weight is a force so is measured in Newtons. Like other forces it has both magnitude (Size) and direction. Mass is not a force, it is measured in kilograms. An astronaut could jump 20 feet into the air on the moon because gravity is less. Would his mass change? And his weight? Weight (N) = Gravitational Field Strength (N/kg) x Mass (kg) W=gxm Use the mass balance to find the mass of an object. Now calculate the weight of this object on other planets in the Solar System. Planet Mass (kg) g-value (N/kg) Mercury 3 Venus 9 Earth 10 Mars 4 Jupiter 26 Saturn 11 Uranus 11 Neptune 12 Pluto 0.5 Weight (N) Weight and Mass So, a scientist should NEVER say “He weighs 50kgs” but, should say “He has a mass of 50kgs”, or the scientist could say: “the gravitational force acting on his mass is about 500 Newtons”. This is the same as saying: “his weight is about 500 Newtons”. Gravity Gravity is an attracting force Everything has gravity Think about it: When you jump the gravitation force of the Earth pulls you down. Your gravitation force pulls the Earth up! Space shuttle - smaller mass Force of gravity The force of gravity depends on the mass of the planet and how close you are to it. Earth - large mass GRAVITATIONAL FORCE Mass = 100g Mass = 100g The force of gravity between 2 apples is very small as they don’t have much mass. Mass = 100g The force of gravity between an Apple and earth is large because Earth has a very high mass. Mass = billions of tonnes LEARNING OUTCOME • Explain why objects weight less on the moon than on the earth. • Describe the effects of the gravitational pull of other planets on the earth. • Explain how rockets can leave the gravitational pull of the earths surface. The Solar System The planets orbit the Sun (not drawn to scale) because it has a massive gravitational pull. The orbits are all ALMOST circular. The shape is called an ellipse. We know next to almost nothing about the Solar System. Mercury planets in our solar system Earth Venus Jupiter Mars My Very Easy Method Just Speeds Up Naming Uranus Saturn Neptune GRAVITY FROM FAR AWAY The force of gravity between objects gets weaker as their separation increases. gravity The moon’s gravity is felt weakly on earth because the moon is so far away and also because the moon is smaller than earth. However, it is strong enough to move water on the earths surface – our tides! http://www.youtube.com/watch?v=p_o4aY7xkXg For a rocket to take off from the earths surface it Must have enough force to overcome the force of gravity. Rockets can burn up to 13 tonnes of fuel per second which creates enough force to lift the rocket away from the surface. http://topdocumentaryfilms.com/when-we-left-earth-nasa-missions/ Answer the questions below in sentences. 1. As the rocket gets further away from the surface of the earth what happens to its gravitational pull? 2. What happens to the mass of the astronauts in a rocket as it moves away from the surface of the earth? 3. For space missions leaving the moon, is more or less fuel needed to leave the surface of the moon than from the earth? Why? LEARNING OUTCOME • Explain what satellites are and how they are kept in orbit. • Describe what geostationary satellites and low polar orbit satellites are. WHY PLANETS ORBIT THE SUN The suns gravitational force is so strong that it keeps planets moving around it. Planets orbit the sun because they are moving and there is a force of gravity. Is there was no gravity, a moving planet would speed off into space. If it wasn’t moving a planet would fall into the sun. WHAT ARE SATELLITES? A satellite is the name for a smaller object that orbits a larger one. Satellites can be natural (the moon is the earths natural satellite and planets are the suns satellites) or man made (artificial). Satellites can be natural (the moon is the earths natural satellite and planets are the suns satellites) or man made (artificial). A satellite will only stay on orbit if it is moving at the right speed for the gravitational pull it feels. Satellites further away must travel more slowly than closer satellites. The time it takes any planet to orbit the sun is its year. Planets further away from the sun have longer years. ARTIFICIAL SATELLITES The Russians launched the first satellite, Sputnik in 1957. Sputnik Now artificial satellites have many different uses and may be manned or stay permanently in space. They are powered using solar panels, and have insulating blankets on their cold side. DIFFERENT TYPES OF ORBIT Geostationary Orbit •Stays at the same point above earth all the time •Moves around the equator •Takes 24 hours to complete its orbit Using Geostationary satellites •Communicate with the same point •Examples include: •High speed phone links •Satellite TV •Computer links •High speed phone links Low Polar Orbit •Can circle the earth in 90 minutes •Can scan the whole earths surface several times in a day. Using Low polar orbit satellites •Produce computer images •Weather reports and imaging •Study crops and forests •Animal migrations •Look for oil / water reservoirs GPS SATELLITES (Global Positioning System) Satellites can be used to find the position of things accurately. The USA created GPS by launching satellites in different orbits, each taking 12 hours to orbit the earth. It is accurate to 3metres. GPS Uses Navigation Surveying Emergency vehicles Applying pesticides / fertilizer HUBBLE Large satellites can takle photographs of the nearby galaxy and can study the sun in more detail. Since the orbit is outside the earths atmosphere the photographs are much clearer then ones from land based telescopes. The Hubble space telescope was launched in 1990 and since then has produced very detailed photographs of distant stars. hubbles universe • http://topdocumentaryfilms.com/theplanets/ • http://www.youtube.com/watch?v=Wk uxGwKqx5U • http://www.youtube.com/watch?v=YY5 79YpDTws&feature=related • http://www.youtube.com/watch?v=euO ubv2OlPA&feature=related LEARNING OUTCOME • Describe early scientific theories on space. LEARNING OUTCOME • State whether two objects of the same mass will reach the ground at the same time when dropped. • Explain this phenomenon. FEATHER_VS_ PENNY_FALLI NG.WMV http://www.youtube.com/watch?v=aCTHVhCQSQs http://www.youtube.com/watch?v=0iDyhg0BPZA http://www.youtube.com/watch?v =NOqR1Csv7yg&feature=BFa&list=SPDE65D78966FEC465&lf=list_related 2 objects when dropped from the same height will have hit the ground at the exact same time regardless of the mass of the object. The only other force acting on the objects will be due to air resistance.
