Prepara tus exámenes y mejora tus resultados gracias a la gran cantidad de recursos disponibles en Docsity
Gana puntos ayudando a otros estudiantes o consíguelos activando un Plan Premium
Prepara tus exámenes
Prepara tus exámenes y mejora tus resultados gracias a la gran cantidad de recursos disponibles en Docsity
Prepara tus exámenes con los documentos que comparten otros estudiantes como tú en Docsity
Encuentra los documentos específicos para los exámenes de tu universidad
Estudia con lecciones y exámenes resueltos basados en los programas académicos de las mejores universidades
Responde a preguntas de exámenes reales y pon a prueba tu preparación
Consigue puntos base para descargar
Gana puntos ayudando a otros estudiantes o consíguelos activando un Plan Premium
Comunidad
Pide ayuda a la comunidad y resuelve tus dudas de estudio
Ebooks gratuitos
Descarga nuestras guías gratuitas sobre técnicas de estudio, métodos para controlar la ansiedad y consejos para la tesis preparadas por los tutores de Docsity
Tema de physics igcse del espacio
Tipo: Apuntes
1 / 34
Esta página no es visible en la vista previa
¡No te pierdas las partes importantes!
describe the orbital motions of the Earth and Moon and relate these to our measures of time
explain the^ movement^ of^ bodies^ in^ the^ Solar^ System^ in^ terms^ of^ gravitational^ attraction
> Chapter^24
Earth and the
Solar (^) System
>
CAMBRIDGE IGCSE™ (^) PHYSICS: COURSEBOOK
) CAMBRIDGE IGCSE™ PHYSICS: COURSEBOOK
position of Earth month
December summer
March autumn (fall) (^) spring
June winter summer
September spring autumn (fall)
Figure 24.4: The Earth (^) orbits the (^) Sun every 365.25 days. (^) The tilt of the Earth causes seasons.
southern hemisphere
northern hemisphere
season winter
As well as the daily changes, early civilisations were aware of periodic changes which happened over a longer time -^ the difference between seasons. The Earth (^) orbits the Sun. It takes just over 365 days to complete one orbit. The seasons occur because of the (^) tilt of the (^) Earth’s axis. Figure 24.4 shows how the seasons change as the Earth orbits the Sun. Consider a country in the northern hemisphere (the half of the Earth north of the Equator). In Figure 24.4a, due to the tilt of the Earth,^ it is tipped away from the Sun and the energy^ from the Sun’s rays is more spread out, making it colder. This means that area receives fewer hours of sunlight. (^) These countries are experiencing winter. In Figure (^) 24.4c, the northern hemisphere (^) is tipped towards the Sun,^ so it receives longer^ hours of more direct sunlight. (^) These countries are experiencing (^) summer.
Years
Figure 24.3: As light travels in straight lines, only half the Earth receives sunlight at any one time.
Earth's axis
24 Earth and the Solar (^) System
axis: the imaginary line between the Earth's North
larger object
divided by the Equator (the) Equator: an imaginary line drawn round the Earth halfway between the North Pole and the South Pole
Countries (^) at the Equator do not experience seasons because the Sun’s rays always (^) hit them at the same angle. The seasonal differences are more apparent the further from the Equator^ you^ are.^ In^ the^ far^ north^ or^ south, seasons are^ so extreme that,^ in^ winter,^ the^ Sun^ is^ hardly seen and,^ in^ summer,^ it^ can^ be^ sunny^ at^ midnight.^ Figure 24.5 (^) shows how, in Alaska, the Sun dips lower in the sky towards midnight^ but then^ starts^ to^ rise^ again.
Figure 24.5:^ This^ multiple^ exposure photograph^ shows^ the position of^ the^ Sun^ in^ the^ hours^ before^ and^ after^ midnight^ in Alaska in midsummer.
Months
The most obvious object in our sky after the Sun is the Moon. The Moon features in many folk tales. It has often been seen as a mystical object due to its fainter light and its changing shape. With the benefit of telescopes and space travel, we know the Moon is a rocky sphere which we only see when it reflects light from the Sun. The Moon orbits Earth^ every^ 27.5^ days.^ Its^ position^ relative^ to^ Earth changes the way it appears to us as different parts of it are^ illuminated^ by^ the^ Sun.^ This^ causes^ the^ changes called the^ phases^ of^ the^ Moon.^ The^ phases^ of^ the^ Moon are shown in Figure 24.6.
first quarter
waning crescent third quarter
Figure 24.6: The phases of the Moon. As the Moon orbits the Earth, the half of the Moon that faces the Sun will be lit up by the Sun. As the Moon moves, the shape of the light part, which can be seen from the Earth, changes. The outer circle of Moon diagrams shows how the Moon looks to an observer on Earth.
phases of the Moon:^ the^ different^ ways the^ Moon
one month
Modelling day, night and seasons
a rod through it^ to represent the Earth.^ Mark your position on^ the^ Earth^ using a^ pen or^ a^ piece of modelling clay. In^ a^ darkened^ area,^ hold^ the 'Earth' near to the 'Sun',^ and^ turn^ the^ Earth^ on^ its axis to model day and^ night. Tilt the Earth on its axis and investigate the seasons by moving the Earth around the Sun. Investigate the difference in seasons between the
Figure 24.7: Model of the Earth and Sun.
>
24 Earth and the Solar (^) System
The Sun's gravitational (^) pull
The orbits of the planets are almost circular. To move (^) in a circle an object needs a force pulling (^) it towards the (^) centre of the circle. Imagine spinning (^) a ball on the end of (^) a piece of string. The ball will spin in a circle as long as you hold on. Once you (^) let go, the ball will fly (^) outwards. The force needed to^ keep^ the planets^ orbiting^ the Sun^ comes from the gravitational^ attraction of the Sun.
The formation of the (^) planets
Evidence collected by^ astronomers suggests that the planets (^) were formed at the same time as the Sun. The Solar System began (^) as a nebula, (^) which is a huge swirling (^) ball of (^) dust and gas. (^) Most of this gas (^) was hydrogen, (^) but there were also other elements formed by^ fusion in other stars, which had exploded^ at the end of their life cycle,^ sending their (^) contents out into the clouds of (^) interstellar gas.
As gravity pulled this mass together, the centre formed a star. You will learn more detail about this in Chapter
The four inner planets, Mercury, Venus, Earth and Mars, are small and rocky. After Mars there is the asteroid belt. This is made up of left-over pieces of rock. The outer four planets, Jupiter, Saturn, Uranus and Neptune, are huge balls of gases. These planets are much bigger than the inner planets.
Figure 24.11: This artist's impression shows a star forming. The uneven, swirling mass of rock and gas around it is flattened by its rapid rotation into an accretion disc where the planets eventually form.
Sun without another similar object close to it
minor planet: an object which orbits the Sun but is not large enough or far enough from another
orbit the Sun
comet: a ball of ice, dust and gas which orbits the
accretion disc: a^ rotating disc of matter formed by accretion
accretion: the coming together of matter under the influence of gravity to form larger bodies
Distances and times in the
Solar System Distances in the Solar System are almost (^) unimaginably big. The Earth is approximately 1 50 million kilometres from the Sun. This is similar to circling the Earth 4000 times. Distances are often expressed in terms of how long it takes light^ to travel;^ one light-year is the distance travelled by^ light^ in a year. The next nearest (^) star after the Sun is Proxima Centauri, (^) which is 4.2 light-years (^) from Earth. You will learn more about light-years in Chapter (^) 25.
Calculate the time for light from the Sun to travel the 150 000 000 km to Earth. Give your answer in minutes.
Step 1: Write down what you know: speed of light (^) = 300 000 000 m/s distance travelled (^) = 1 50 000 000 km
Step 2: (^) Convert distance to (^) metres, so units are consistent. 150 000 000 km (^) = 1 50 000 000 000 m
457 y
> CAMBRIDGE IGCSE™ PHYSICS: COURSEBOOK
Step 3: Write the equation down and calculate the time taken:
timeQ^ taken -^ distance^ travelled speed _ (^150000000000) m 300 000 000 m/s = 500 seconds
Step 4: Convert to minutes 500 -9- (^60) = 8.3 minutes
Answer 8.3 minutes
Questions (^4) The Moon is approximately 390 000 km from Earth. Calculate the time it takes for light to travel from the Moon to the (^) Earth. 5 How long will (^) it take for light from the Sun to reach: a Mercury, which is approximately 60 000 000 km from the Sun. b Neptune, which is approximately 4 500 000 000 km from the Sun.
6 It takes sunlight 43 minutes tb reach Jupiter. Calculate the distance from Jupiter to the Sun. 7 Calculate how many (^) kilometres a light-year is equivalent (^) to.
More (^) about the (^) planets Table (^) 24.1 gives (^) data about the planets in the Solar System. It (^) shows how the planets (^) differ from each other, for example looking up from (^) the surface of Jupiter (^) you might see (^16) moons.
Forces The Sun is at the centre of the Solar System. It is by far the most massive object in the Solar System (^) and makes up about 99.8% of the mass of (^) the Solar System. As gravitational attraction depends on mass, the gravitational field strength of the Sun is far larger than the field of any other object in the Solar System. The planets, minor planets, asteroids and meteoroids and comets all orbit the Sun. They are held in orbit by the gravitational (^) attraction of the Sun. Like other non-contact forces such as (^) magnetism and static electricity, gravitational (^) attraction decreases with distance. This means that (^) the outer planets experience
planets (^) do.
Table 24.
Planet
Average orbital distance / million km
Orbital duration (^) / years
Density / kg/ m’
Surface temperature /°C
Gravitational field strength at the surface of
N/kg
Number of Moons
Mercury (^58) 0.2 5500 -18 to 460 4 0 Venus 108 0.6 (^5200 470 9 ) Earth (^150 1 5500) -8 to 58 10 1 Mars 228 1.9 4000 -8 to -5 (^4 ) Jupiter 778 12 1300 15 to 20 26 16 Saturn 1427 30 700 -140 (^11 ) Uranus (^2870 84 1300) -200 11 15 Neptune 4497 165 1700 -220 (^12 )
458 y
) CAMBRIDGE IGCSE™ PHYSICS: COURSEBOOK
Figure 24.14: To calculate the orbital (^) speed, we assume that the orbits are circular.
The distance (^) travelled by (^) the planet (^) is the circumference of its (^) orbit. The circumference of a circle is equal to 2w. If we also know the time for the planet to orbit the Sun
speed (^) = distance time
So, the average (^) orbital speed v, can be calculated from its (^) orbital period, T, (^) and its average orbital radius r, using the equation:
, , 2 x (^) n x (^) orbital radius average (^) orbital speed (^) = (^) — orbital period ___ (^) 2nr v (^) =
orbital (^) radius: the (^) average distance of the planet from the Sun
orbital period: the time taken for a (^) planet to
Calculate the orbital speed of Earth. Step 1: Write down what you (^) know: r (^) = 150 000 000 km T (^) = 1 year Step 2: Convert (^) T to seconds. 1 year (^) = 1 x^365 = 365 days 365 days (^) = 365 x^24 = 8760 hours 8760 hours (^) = 8760 x^60 x^60 = 31 536000 seconds Step 3: Substitute values for (^) T and (^) r into the equation and calculate v. _ (^) 2w v (^) = T
=
2^x (^150000000) km 3 1 536000s = 30km/s Answer 30km/s
Planetary (^) patterns Much of what astronomers have (^) discovered has been through observing (^) the skies, (^) gathering huge amounts of data and then looking^ for patterns in the data. Ancient astronomers knew the planets were different from the (^) stars because of the way their positions in the sky changed. Mercury was named by ancient Greeks after the messenger of the gods, (^) which is (^) a fitting name for the planet which orbits the Sun faster than any other. Sometimes we can learn as much from observations that are exceptions to a pattern as from those that fit our predictions. The (^) data in Table 24. 1 can be used to investigate pattern* in the properties and behaviours of planets. Plotting data on a scatter (^) graph can give a clear indication of whether there is a correlation between two sets of data. For example, (^) a graph of density against distance from the Sun (Figure 24.15) shows that there is not a (^) clear correlation between the two. However, it is clear that the four inner rocky planets are more dense than the outer gas (^) giants.
460 >
24 Earth and the Solar System
Figure 24.15: There is a pattern in this data but not a direct correlation.
Questions 8 a Name the force which causes planets to orbit the Sun. b What shape are planetary^ orbits? c How is the orbit of a comet different to the orbit of a planet? d Describe the energy changes in a comet as (^) it orbits the Sun. 9 Calculate the weight of a 30 kg sheep on: a Earth b Mars c Jupiter. 1 0 Use information from Table 24. 1 to calculate the orbital speeds in m/s of: a Venus b Saturn. 11 Using Table 24.1, draw and comment on scatter graphs to investigate the relationship between: a orbital distance and average temperature b gravitational field strength and the number of moons.
Solar System quiz Some great ways of learning are:
you become an (^) expert on our Solar System. Make (^) up a (^) quiz about the Solar System. The (^) quiz can be on (^) paper, the (^) computer, or on a mobile
good (^) quiz making (^) apps available). (^) It should be
and who have a good^ general knowledge.^ Spend some time revising and researching to find interesting facts to^ include.^ You^ may want^ to^ rate questions as^ 'easy',^ 'medium'^ or^ 'hard'^ and^ give more (^) points for harder (^) questions. You (^) can include mathematical (^) questions and (^) questions which require data^ interpretation. You^ should^ include^ at least (^20) questions. Think about how you will (^) group your questions. You^ could include:
any object in the Solar System', and ask what is being defined.
461 y
24 Earth and the Solar System
Which of the following objects is a planet? A the Moon B Hale-Bopp C Pluto
Which (^) statement about the orbits of (^) the Earth and Moon is correct? [1]
The diagram (^) shows how people 1000 years ago thought (^) the Solar System (^) looked.
[1] b [1]
[1] d [1]
i (^) XAM-STYLE QUESTIONS
calculate: work out from (^) given facts, figures or information
The Moon rotates on its axis in 24 hours and orbits (^) the Earth in 27.5 days. The Earth rotates on its axis in 24 hours and orbits (^) the Sun (^) in 365 days. The Moon orbits the Sun in 27.5 days. The Earth rotates on its axis in 24 hours and orbits the Moon in 27.5 days.
State one way in which this model is different from what we now know about the Solar System. State one^ way^ in which this model is^ similar to what we now know about the (^) Solar System. State one way in which the planets Mercury, Venus, (^) Earth and Mars (^) are similar. State one way in which Jupiter and Saturn are different to the planets in part c. Mars is 228 million km from the Sun. Calculate the time it takes for light
state: express in clear terms
What force keeps the planets in orbit round the (^) Sun? A momentum B air resistance C tension
[3] [Total: 7]
[1] D Uranus
When an orbiting object is at its closest to the Sun, it has its maximum kinetic energy and minimum gravitational potential energy. Planetary (^) data about orbital distance, (^) orbital duration, density, surface temperature and gravitational field strength can be analysed to show patterns in the properties and behaviour (^) of the planets.
[1] D gravity
5 Laurie is standing at point (^) X on the (^) Earth’s surface.
N Moon Earth X
S
6 The table shows some data about the objects orbiting (^) the Sun.
Use the information in the table to answer the following questions.
c [2] d [2] e
light from the Sun
[1] [
m m
[i] tn [2]
characteristics and main features
explain: set (^) out purposes or reasons; make
between th (^) jigs
why and/or how .in< I
evidence
a b
a b
d e f
How can you tell it is night time at point X? Redraw the diagram^ to show where point X will be after 12 hours. The Moon does not emit light. Explain how Laurie is able to see the Moon. Name the force which keeps the (^) Moon in orbit around the Earth. Describe the movement of the Moon. A ball dropped on Earth will fall faster than an identical ball dropped on the Moon. What does this tell you about the Moon’s gravity?
Name the object that is not a planet. Which (^) planet takes the least time to go round the Sun? A (^) student writes, (^) ‘the further away from the Sun a planet is, the lower its density’. To what (^) extent do you agree (^) with this statement? What data from the table suggests (^) that Pluto and Mars are the two least massive objects? Calculate the average orbital speed of Jupiter. Give your (^) answer in km/s to two significant figures. [3] [Total: 9]
[1] [Total: 7]
Object
Distance from Sun / million km
Average surface temperature / °C
Density / kg/m
Surface gravity / N/kg
Time of
years Venus (^108 470 5200 9) 0. | Earth (^150 15 5500 10) 1. Mars (^228) -30 4000 5 1. | Jupiter 778 -150^1300 26 Saturn (^1427) -180 700 11 30 | Pluto^5900 -230 500 4 248
learn that the redshift of (^) light from (^) distant galaxies supports the Big Bang theory
describe the Sun and galaxies, including the Milky (^) Way
learn that this redshift can be described by (^) Hubble's law, which can (^) be used to work out the age of the Universe.
describe how stable stars (such (^) as the Sun) are (^) powered by the thermonuclear fusion of hydrogen
25 Stars and the Universe
Spend two^ minutes^ thinking^ about^ these^ questions before (^) comparing notes with your neighbour for a further two minutes, adding to or correcting your
the class.
Where does the Sun get its energy? What colour are stars? What is a galaxy and what is the name of our galaxy? List what you know about the Universe.
We know many things about the Sun but a lot^ of^ that knowledge has been gained very recently. Working out what makes the Sun shine was a^ process of
found that best fits the evidence.
forever. However, in 1613, Galileo Galilei observed
showed that the Sun could not be made of ether.
Coal was burned in steam engines to power the UK's Industrial Revolution. This^ made scientists wonder whether the Sun was a giant lump of coal but calculations showed that a Sun made^ of coal would shine for less than 1 500 years and this is a shorter time than recorded history. However, efforts
conservation of energy. This led scientists to look^ for other sources of energy (that^ could be transferred by light).
Scientists like Hermann von Helmholtz believed
colliding with the Sun could be this source of energy. However,^ the^ total^ mass^ of^ meteorites^ was too small^ and^ they^ were^ not^ moving^ fast^ enough^ to
Other scientists imagined that the Sun^ was^ once much bigger so that it only just fitted inside^ the Earth's orbit. But the gravitational energy released
which was not enough time for the evolution of
Then radioactivity was discovered, and Einstein showed that mass can be transformed into energy.
This led scientists to work out that the Sun is
formed theory did not (^) appear until 1939.
Figure 25.1: The Sun shining.
Discussion questions
to believe about what makes the Sun shine. For each one, write down how scientists showed that the belief was incorrect.
467 y
(^25) Stars and the Universe
Activity 25.1?
that the Sun is not yellow, did you know what
Were you able to think objectively and find
makes the Sun shine? that led to correctly understanding how^ stars shine.
25.2 Stars and galaxies When you^ look^ into^ the^ night^ sky,^ the^ light^ that^ you ."c from^ the^ stars^ has^ been^ travelling^ for^ many^ years. A (^) Nt i onomers use (^) this idea as a way of measuring (^) vast
I line).^ It^ is the^ distance that^ light^ travels through^ space^ in line year.^ Light^ travels^ at^ a constant speed^ of^3 x^ 108m/s llirough a (^) vacuum. This means that the (^) time it takes to I ravel somewhere^ is^ directly^ proportional^ to^ distance. < )nc^ light-year is the distance that light travels in one year,
illatance (^) = speed^ x^ time So, (^) one light-year (^) = 3 x (^) 108m/s x (^) 365.25 days x (^24) hours 3600 seconds (^) = 9.5 x^ 10l5m.
Mar is^ Proxima^ Centauri,^ which^ is^ about 4.2^ light-years ijway. When^ you^ see^ Proxima^ Centauri^ the^ light^ left^ it
lis because^ the^ Sun is^ much^ closer to us. Pluto has an oil iptical orbit but, on average, it is 40 times further from Ilie Sun than the Earth is. But this is (^) dwarfed by (^) the
Questions 5 The Sun is about eight light-minutes away. It takes sunlight about eight minutes to reach Earth on its journey from the Sun. a Given that the speed of light is 3 x^ 108m/s, how far away is the Sun in kilometres? b How many years would it take a car to get to the Sun travelling at 120 km/h? 6 After our Sun, (^) Proxima Centauri is (^) our next nearest star. It is about 4.2 light-years away. a How many seconds does it (^) take light from Proxima Centauri to reach Earth?
c Helios I & II hold the record as the fastest ever space probes at 252 738 km/h (about 70 km/s). How many years would it take these space probes to reach Proxima Centauri? d How long would it take them to reach the nearest galaxy 25 000 light-years away from us? The force^ of^ gravity^ pulls^ stars together^ in groups called galaxies. Our Sun is one of many (^) billions of (^) stars in our
stars in the Milky Way, about 20 stars for every person on Earth. The Milky Way is a spiral galaxy with a central bulge (see Figure 25.2). It has a diameter of 100 000 light- years and the disc is about 2000 light-years thick. Our Solar System is located about 30 000 light-years from the galactic centre, two-thirds of the way along a spiral^ arm. The Milky Way (^) is spinning (^) and it takes our Solar System (^) about 225 million years to travel once around the galaxy.
The Milky Way is one of many billions of galaxies, that make up the Universe. Most people consider the Andromeda Galaxy (Figure 25.3) to be our closest galactic neighbour and it is certainly our closest spiral galaxy. However, our nearest galactic neighbour is the Canis Major
> CAMBRIDGE IGCSE™ PHYSICS: COURSEBOOK
Dwarf Galaxy, which is 25 000 light-years away from us and 42 000 light-years from the centre of the Milky Way.
Figure 25.3: An infrared image of the Andromeda Galaxy, our closest spiral galaxy.
Questions 7 a Make two sketches to show the Milky Way Galaxy; one sketch should show its spiral structure and the other should show the galaxy edge on. b On your sketches mark the diameter of the Milky Way in light-years. c Mark the position^ of the Sun in the Milky Way.
8 The Solar System^ has existed for 4.6 billion years. How many^ times has the Solar System^ travelled around the Milky^ Way^ in^ that time? 9 How can the Canis Major Dwarf Galaxy be closer to us (^) than we are to the centre of our own galaxy?
1 0 Assuming that the average mass of a star is equal to
of the Milky Way?
11 Imagine that the Milky Way is shrunk down to fit into the space between the Earth and the Sun. On this scale, calculate how far away the following bodies would be from Earth: a Proxima Centauri (in^ km) b (^) Pluto (in km) c the Sun (in metres) d the Moon (in cm).
1 2 Write a sentence or two comparing your answers to question 25.1 1 with the length of a pencil, the length^ of a cricket pitch (about^20 metres),^ a 400 metre athletics track, and the radius of the Earth (6400 km).
How do astronomers measure distances (^) to faraway objects?
distances in (^) space. For nearby stars within (^) our
viewed from (^) opposite sides of our orbit around the Sun, as shown in (^) Figure 25.4. You can^ experience this yourself.^ Stretch^ out
Close one (^) eye and (^) open the (^) other and (^) then
should appear to^ move from side to side agaim-t the background (which^ should be at least two .urn lengths away).
background stars ^y^ (^) & \ / (^) * cVstar / /i\ ,para^ lax^ angle^ /
/ (^) / Earth in summer jr"^ Q Earth (^) in wlnb A"- ' —""B
Figure 25.4: Parallax in nearby stars.
the summer it appears to be at location X againiJ
(shown by the dashed line from B), the astrononv
to (^) position Y against the background stars. 1 In (^) groups, use the (^) biggest space available to you to mark out three positions to (^) represent
roughly south of A and B. Ensure that the
between the Sun and the star.
(^470) )
