EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 1-6AstronomyEdexcel IGCSE Physics pages 49 to 56June 17th 2011All content applies for Triple & Double Science

Edexcel SpecificationSection 1: Forces and motiond) Astronomyunderstand gravitational field strength, g, and know that it is different on other planets and the moon from that on the Earth.explain that gravitational force:- causes moons to orbit planets- causes the planets to orbit the sun- causes the moon and artificial satellites to orbit the Earth- causes comets to orbit the sundescribe the differences in the orbits of comets, moons and planetsuse the relationship: orbital speed = (2 orbital radius) / time periodv = (2 r) / Tunderstand that:- the universe is a large collection of billions of galaxies- a galaxy is a large collection of billions of stars- our solar system is in the Milky Way galaxy.

The Solar SystemThe Solar System consists of the Sun orbited by eight planets and their moons, some dwarf planets along with many asteroids and comets.

PlanetsA planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has cleared its neighbourhood of smaller objects around its orbit.

Based on this, International Astronomical Unions definition of 2006, there are only eight planets in orbit around the Sun.In order of distance from the Sun:

Dwarf PlanetsA dwarf planet is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity. but has not cleared its neighbouring region of other similar bodies.As of 2011 there are five dwarf planets in the Solar System.Between Mars and Jupiter: CeresBeyond Neptune: Pluto, Haumea, Makemake and Eris (the largest)

AsteroidsAn asteroid is a celestial body orbiting the Sun that is not massive enough to be spherical as a result of its own gravity.

Most asteroids are found between the orbits of Mars and Jupiter a region called The Asteroid Belt.

There are about 750 000 asteroids larger than 1km across.

A few, called Near Earth Asteroids can pass very close to the Earth.

MoonsA moon orbits a planet.The Earths only natural satelliteNote: A number of dwarf planets and asteroids also have moons, for example Pluto has three moons.

This is the time taken for a planet to complete one orbit around the Sun.

It increases with a planets distance from the Sun.

Time period (T )

Gravitational attractionThe force of gravity is responsible for the orbits of planets, moons, asteroids and comets.

In 1687 Sir Isaac Newton stated that this gravitational force:- is always attractive- would double if either the mass of Sun or the planet was doubled- decreases by a factor of 4 as the distance between the Sun and a planet doubles.

Gravitational field strength (g)This is a way of measuring the strength of gravity.

The gravitational field strength is equal to the gravitational force exerted per kilogram.

Near the Earths surface, g = 10 N/kg

In most cases gravitational field strength in N/kg is numerically equal to the acceleration due to gravity in m/s2, hence they both use the same symbol g.

Gravitational field strength (g) varies from planet to planet.

It is greatest near the most massive objects.

Some examples of gravitational field strength:

Planetary orbitsThe orbits of the planets are slightly squashed circles (ellipses) with the Sun quite close to the centre.

The Sun lies at a focus of the ellipse

Planets move more quickly when they are closer to the Sun.

The above diagram is exaggerated!

What would happen to an orbit without gravityAs the red planet moves it is continually pulled by gravity towards the Sun.

Gravity therefore causes the planet to move along a circular path an orbit.

If this gravity is removed the planet will continue to move along a straight line at a tangent to its original orbit.

CometsA comet is a body made of dust and ice that occupies a highly elongated orbit.

When the comet passes close to the Sun some of the comets frozen gases evaporate. These form a long tail that shines in the sunlight.

Comets are most visible and travel quickest when close to the Sun.

Comets are approximately 1-30km in diameter.

Halleys CometThis is perhaps the most famous comet.

It returns to the inner Solar System every 75 to 76 years. It last appeared in 1986 and is due to return in 2061.

It has been observed since at least 240BC. In 1705 Edmund Halley correctly predicted its reappearance in 1758.

Choose appropriate words to fill in the gaps below:The Solar System consists of a ______, the Sun, orbited by _______ planets, a number of dwarf planets and millions of asteroids and ________.All of these bodies ______ the Sun because of gravitational force. Gravity is also responsible for the orbits of _______ and artificial satellites.Most orbits are nearly circular _______ but those of comets are highly elongated. Comets move ________ when they are at their nearest to the SunquickesteightstarcometsellipsesWORD SELECTION:orbitmoonsquickesteightstarcometsellipsesorbitmoons

Orbital speed (v)orbital speed = (2 x orbital radius) / time period

v = (2 x r ) / T

orbital speed in metres per second (m/s)orbital radius in metres (m)time period in seconds (s)

Question 1Calculate the orbital speed of the Earth around the Sun. (Earth orbital radius = 150 million km)v = (2 x r ) / T

= (2 x [150 000 000 km] ) / [1 year]but 1 year = (365 x 24 x 60 x 60) seconds= 31 536 000 sand 150 000 000 km = 150 000 000 000 metres

v = (2 x [150 000 000 000] ) / [31 536 000]orbital speed = 29 900 m/s

Question 2Calculate the orbital speed of the Moon around the Earth. (Moon orbital radius = 380 000 km; orbit time = 27.3 days)v = (2 x r ) / T

= (2 x [380 000 km] ) / [27.3 days]but 27.3 days = (27.3 x 24 x 60 x 60) seconds= 2 359 000 sand 380 000 km = 380 000 000 metres

v = (2 x [380 000 000] ) / [2 359 000]orbital speed = 1 012 m/s

Question 3Calculate the orbital speed of the ISS (International Space Station) around the Earth. (ISS orbital height = 355 km; orbit time = 91 minutes; Earth radius = 6 378 km)

The orbit radius of the ISS = (355 + 6 378) km = 6 733 kmv = (2 x r ) / T

= (2 x [6 733 km] ) / [91 minutes]but 91 minutes = (91 x 60) seconds= 5 460 sand 6 733 km = 6 733 000 metres

v = (2 x [6 733 000] ) / [5 460]orbital speed = 7 748 m/s

Question 4Calculate the orbital time of a satellite that has a speed of 3 075 m/s and height above the earth of 35 906 km. (Earth radius = 6 378 km)

The orbit radius of the satellite = (35 576 + 6 378) km = 42 284 kmv = (2 x r ) / Tbecomes: T = (2 x r ) / v= (2 x [42 284 km] ) / [3 075 m/s]but 42 284 km = 42 284 000 metresT = (2 x [41 954 000 ] ) / [3 075 ]orbital time = 86 400 seconds= 1440 minutes= 24 hours

Communication satellitesThese are usually placed in geostationary orbits so that they always stay above the same place on the Earths surface.VIEW FROM ABOVE THE NORTH POLE

Geostationary satellites must have orbits that:- take 24 hours to complete- circle in the same direction as the Earths spin- are above the equator- orbit at a height of about 36 000 km

Uses of communication satellites include satellite TV and some weather satellites.

Choose appropriate words to fill in the gaps below:A satellite is a ________ mass object orbiting around a ________ mass body.The larger the orbit of a satellite the more ________ it moves and the ________ it takes to complete one orbit.Geostationary satellites are used for _____________ and have an orbital period of _____ hours._____________ satellites normally use polar orbits.24lowerlongerslowlycommunicationsWORD SELECTION:highermonitoring24lowerlongerslowlycommunicationshighermonitoring

The Milky WayThe Milky Way is the name of our galaxy.

From Earth we can see our galaxy edge-on. In a very dark sky it appears like a cloud across the sky resembling a strip of spilt milk.

GalaxiesGalaxies consist of billions of stars bound together by the force of gravity.

There are thought to be at least 200 billion galaxies in our Universe each containing on average 2 billion stars.

Types of galaxy

Choose appropriate words to fill in the gaps below:The ___________ is made up of billions of galaxies which consist of __________ of stars bound to each other by the force of ___________.The name of our _________ is The Milky Way. The ______ is located towards the outer edge of our galaxy.The are different types of galaxy; ________, barred-spiral, elliptical and irregular. The Milky Way is a ____________ galaxy. The _____________ Galaxy is the nearest spiral galaxy to the Milky Way.spiralgalaxygravitybillionsSunbarred-spiralWORD SELECTION:UniverseAndromedaspiralgalaxygravitybillionsSunbarred-spiralUniverseAndromeda

Online SimulationsMy Solar System - PhET- Build your own system of heavenly bodies and watch the gravitational ballet. With this orbit simulator, you can set initial positions, velocities, and masses of 2, 3, or 4 bodies, and then see them orbit each other. Multiple planets - 7stones Planet orbit info - Fendt Distances in Space - Powerpoint presentation by JAA Solar system quizes - How well do you know the solar system? This resource contains whiteboard activities to order and name the planets corrrectly as well as a palnet database - by eChalk Hidden Pairs Game on Planet Facts - by KT - Microsoft WORD Fifty-Fifty Game on Planets with Atmospheres - by KT - Microsoft WORD Fifty-Fifty Game on Planets that are smaller than the Earth - by KT - Microsoft WORD Sequential Puzzle on Planet Order - by KT - Microsoft WORD Sequential Puzzle on Planet Size - by KT - Microsoft WORD Lunar Eclipse - flash demo Phases of the Moon - Freezeway.com Phases of the Moon - eChalk Seasons - Freezeway.com

Gravity & Orbits - PhET - Move the sun, earth, moon and space station to see how it affects their gravitational forces and orbital paths. Visualize the sizes and distances between different heavenly bodies, and turn off gravity to see what would happen without it! Projectile & Satellite Orbits - NTNU Newton's Cannon Demo - to show how orbits occur - by Michael Fowler Kepler Motion - NTNU Kepler's 2nd Law - Fendt Two & Three Body Orbits - 7stones Orbits - Gravitation program BBC KS3 Bitesize Revision: The Solar System Gravitational Forces Days & Nights Years & Seasons - includes an applet showing the tilt of the Earth The Moon Artificial space probes and satellites

AstronomyNotes questions from pages 49 to 56Outline the structure of the Solar System and explain the difference between a planet and a moon. (see pages 49 to 50)Define what is meant by gravitational field strength and explain how it may differ throughout the Solar System. (see page 50)How is the orbit of a comet different from a planet? (see pages 51 and 52)(a) Give the equation for orbital speed. (b) Calculate the orbital speed of Mercury around the Sun. [Mercury orbital radius = 58 million km; orbital time = 88 days]. (see page 54)(a) What is the Milky Way? (b) What is a galaxy? (c) How many galaxies are there in the Universe? (see page 55)

Answer the questions on page 56.Verify that you can do all of the items listed in the end of chapter checklist on page 56.

*********