What is out there? 25/01/2016 cgrahamphysics.com Book page Syllabus

Transcription

1 What is out there? Book page Syllabus

2 Starter How many stars are there in the solar system? What is the solar system made up of? What is the Universe made up off?

3 Whenever life gets you down, Mrs. Brown, and things seem hard or tough,

4 and people are stupid, obnoxious or daft, and you feel that you've had quite eno-o-o-o-o-ough...

5 900 mph just remember that you're standing on a planet that's evolving and revolving at nine hundred miles an hour,

6 19 mps 19 mps that's orbiting at nineteen miles a second, so it's reckoned, a sun that is the source of all our power.

7 the sun and you and me and all the stars that we can see are moving at a million miles a day

8 mph in an outer spiral arm, at forty thousand miles an hour, of the galaxy we 25/01/2016 call the milky cgrahamphysics.com way. 2016

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12 Our galaxy itself contains a hundred billion stars, it's a hundred thousand light years side to side.

13 ly 3000 ly it bulges in the middle, sixteen thousand light years thick, but out by us, it's just three thousand light years wide.

14 yr we're thirty thousand light years from galactic central point, we go round every two hundred million years,

15 and our galaxy is only one of millions of billions in this amazing and expanding universe.

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26 The universe itself keeps on expanding and expanding in all of the directions it can whizz

27 as fast as it can go, at the speed of light, you know, twelve million miles a minute, and that's the fastest speed there is.

28 So remember, when you're feeling very small and insecure, how amazingly unlikely is your birth,

29 and pray that there's intelligent life somewhere up in space, cause there's bugger all down here on earth!

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31 Aim (a) What are galaxies and where is the solar system in our galaxy? (b) What is the universe made up of? (c) What keeps objects in their celestial path? (d) How can we calculate the speed of satellites or planets in an orbital path?

32 Galaxy 은하, 은하수 Milky way 은하, 은하수 Star 별 Sun 태양 Planet 행성 Asteroid 소행성 Comet 혜성 Solar system 태양계 Earth 지구 Moon 달 Key Words

33 How long does it take the Earth to turn on its axis?

34 Spinning Around The Sun appears to travel east-west across the sky once every 24 hours The stars appear to travel east-west across the sky once in a very slightly shorter time period The Moon appears to travel eastwest once in a slightly longer time period

35 Gravitational forces keep the planets spinning around the Sun and the Moon around Earth The apparent motions of the Sun, stars, Moon and planets are caused by the rotation of the Earth and the orbits of the Earth, Moon and planets

36 What is gravity? Gravity is a universal force that attracts any mass to every other mass in the Universe. Every mass has its own gravitational field but it takes two objects to make a gravitational force. Gravity is a very weak force compared with other forces Gravitational force causes - Moons to orbit planets - Planets to orbit the Sun - artificial satellites to orbit Earth - Comets to orbit the Sun

37 Factors affecting gravity The bigger the mass, the stronger its gravitational field, Sun has a much stronger gravitational field than Earth. The further apart two objects are, the weaker the gravitational forces between them. Gravitational fields are stronger: around larger masses at shorter distances. The gravitational force between two objects can be increased: by increasing the size of either or both of the masses by decreasing the distance between them.

38 How distance affects gravity Decreasing the distance between two objects decreases the gravitational force between them. Suppose Earth had two moons, and one was twice as far away from Earth as the other. How would the gravitational force from the Earth felt by each moon compare? F F/4 d d Gravitational force decreases with the square of the distance. This is the inverse square law. If the distance between the masses is doubled, the forces between them are quartered

39 Understanding gravity

40 What is the solar system made up of? Star Planets Moons Asteroid Belt Comets

41 Stars What is a Star? A star is a massive, luminous ball of reacting gas All stars have a life cycle which takes billions of years Our Sun is a star, but just one of many millions in our galaxy The closet star to our solar system, apart from the Sun, is called Alpha Centauri

42 If we consider the Earth as the size of a marble, and the distance between it and the Sun as 280 meters then the star Alpha Centauri should be placed 78,000 kilometers away!

43 Where are we? Our Planet is one of a number in the solar system: Planets are non luminous Planets Song Video.mp4 What s wrong with this picture?

44 Planets Our solar system contains nine planets, with each one orbiting the Sun Many of the planets have moons which orbit around them Planets were named after Romans and Greek gods Other galaxies have planets, but they are very hard to find

45 Moons Moons are natural satellites that orbit planets The Earths Moon is simply known as the moon but other planets have moons with proper names Jupiter has lots of Moons but we know lots of details about the inner four Callisto, Io, Ganymede and Europa It takes 25/01/2016 the moon 29.5 days one cgrahamphysics.com lunar month 2016 to orbit Earth

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47 Between the orbits of Mars and Jupiter there is an asteroid belt the asteroids that make it up are large irregularly shaped pieces of rock Asteroid Belt

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49 Comets A comet is a small object in the Solar System that orbits the Sun Occasionally they are visible from Earth as they pass by

50 Comets have a different path Asteroids orbit the Sun between Jupiter and Mars However, comets follow a highly elliptical path They originate in the Ort cloud or the Kuiper belt

51 Comets The head of the comet is a lump of ice and dust a few kilometres across. The tail only appears when the comet is near the Sun. It consists of gas and dust which are released by the heat of the Sun. gas tail dust tail

52 The orbit of a comet

53 Artificial Satellites Geostationary Polar orbiting Geostationary satellites are particularly useful because they stay fixed above a single point on Earth. Polar satellites are particularly useful because they orbit at a low altitude and high speed.

54 Types of orbit

55 Geostationary satellites They are useful for communications and satellite TV broadcasting, because the satellite never goes out of range. Geostationary satellites are also used for weather forecasting.

56 Problems with geostationary satellites All geostationary satellites must orbit over the equator at a specific altitude of 36,000 km. There are limited slots in this orbit, which can lead to disputes when different countries want a certain slot. A geostationary satellite can only see a certain area of the Earth s surface the rest is hidden from view. All geostationary satellites are a long way from Earth, which causes delays in signals. This can be a disadvantage during commercial or military communications.

57 Uses for polar orbit satellites They are used for mapping, as they can image the Earth s surface in higher resolution than more distant satellites. Observation purposes, such as military surveillance, or weather monitoring, as they can view the whole of the Earth s surface in one day. Disadvantage: Polar satellites must be tracked from the ground, and will be out of range for much of the time, causing delays in data retrieval.

58 Orbit height and speed A satellite orbiting the Earth at a lower altitude needs to travel faster to stay in orbit. Geostationary Satellites are in higher orbits because they travel slower at about 3km/s Monitoring Satellites are at lower altitude and travel faster at about 8km/s Gravitational force provides centripetal acceleration This means the force is always pointing towards the center of orbital motion Although speed of satellites is constant, they are accelerating because direction is changing

59 Orbital Speeds How could we calculate how fast a planet or a satellite is travelling as it orbiting? What simplifications would be useful? 1. Consider the orbit circular 2. To find the distance, find the circumference of the circle by using C = 2πR 3. Find the period T for one complete orbit 4. Use the formula for speed v = d t where d = circumference t = period T

60 Orbital Speeds Orbital Speed (km/s or m/) = v = 2πR T 2 π orbital radius (km or m) time period( s) Example Calculate the speed of a satellite that is orbiting 200km above earth s surface and v completes one orbit in 1 h 24 min. The radius of Earth is 6400km. Solution Orbital period T = min= 84 min x 60sec = 5040s v = 2πR T = 2π = 8.2km/s 2πR : : T

61 The big picture: our Universe Earth Solar System Milky Way Cluster of Galaxies Super cluster of galaxies the Universe

62 Galaxies Our solar system is contained within a galaxy called the Milky way Each galaxy is made up of several star systems The universe itself is made up of many billions of galaxies Scientists are able to photograph them from Earth and in space using the Hubble Space Telescope How Big is the Universe_ - YouTube [720p].mp4

63 Review: What is a Comet = a small extra-terrestrial body consisting of ice and dust that has a highly elliptical orbit Asteroid = small object in orbit around the sun composed mostly of rock. Meteor = any of the small solid extra-terrestrial bodies that hits the earth's atmosphere

64 Which type of satellite?