EARTH, MOON AND SUN REVIEW

ANSWERSYear 7 Science

Chapter 2.2 page 343(2) Name one thing that is currently pulling you with a strong gravitational force.

The Earth is currently exerting a strong gravitational pull.

(3) Name one:

◦ a natural satellite of the Sun

◦Natural satellites of the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, the dwarf planets and comets.

◦ b natural satellite of Earth

◦ The only natural satellite of Earth is the Moon.

◦ c artificial satellite of Earth.

◦ Artificial satellites of Earth include communication satellites, the Hubble Space Telescope, the International Space Station (ISS) and space junk.

(4) Recall how gravity changes with distance by ranking the following from the place which would have the highest gravity to the place with the lowest gravity.

A On top of Mt Kosciuszko (New South Wales), the tallest mountain in Australia (2228 m).

B At the top of Q1 tower (Queensland), the tallest building in Australia (323 m)

C On Bells Beach (Victoria) (sea level)

D On the edge of the Lake Eyre (South Australia) (15 m below sea level)

Highest gravity to lowest gravity: D (Lake Eyre), C (Bells Beach), B (Q1 tower), A (Mt Kosciuszko)

(5) State how many high tides and how many low tides will be experienced every day at the docks in Fremantle, Western Australia.

There will be two high tides and two low tides.

Chapter 2.2 page 343

Chapter 2.2 page 343(9) The times for high and low tides differ around Australia. Explain why.

The times for high and low tides differ around Australia because Australia’s coastline covers hundreds of kilometres east to west.

(13) Identify whether a neap or a spring tide produces greater changes in sea levels. Use a diagram to explain your answer.

Spring tides produce greater changes in sea levels than neap tides. This is because the Sun and Moon are both pulling in the same direction. Neap tides are caused by the Sun and Moon pulling perpendicular to each other.

Chapter 2.3 page 350(1) State which of the following is correct. Earth spins from:

A north to south

B east to west

C south to north

D west to east

(2) Recall the following terms by matching each with the correct number of days:

◦A year 365.25 days

◦A ‘normal’ calendar year 366 days

◦A leap year 366 days

Chapter 2.3 page 350(3) Define the following terms:

◦ a 1 day 1 day is the time taken for a planet to rotate on its own axis (for Earth 24 hours).

◦b 1 year 1 year is the time taken for a planet to revolve once around the Sun (for Earth 365.25 days)

◦ c 1 revolution. 1 revolution = 1 complete orbit

(4) Describe the problems that would be caused if our calendar year was taken as 36514 and not 365 and 366 days.

If the calendar year was taken as 365¼ days, then each year would start 6 hours later than the previous one. This would make every fourth year ‘out’ by one day.

Chapter 2.3 page 350(5) Explain why tropical countries are located around the equator.

The tropics are found near the equator because that is where sunlight falls more directly, concentrating its light and heat. Hence the climate there is hot throughout the year.

(6) The equinox marks the time in the year that the length of day and night are exactly the same. Predict:

a how many equinoxes occur each year

There are two equinoxes each year.

b the seasons they occur in

One equinox occurs in autumn and the other in spring.

Chapter 2.3 page 350

(7) Use a sketch to help define the following terms:

◦ a Earth’s axis

◦b the equator

◦ c the poles.

(8) Some people only have a birthday every four

years. Identify the date on which they were born.

They were born on 29 February (a leap year

and hence only occurring every fourth year)Earth’s axis

the poles

the poles

equator

Chapter 2.3 page 350

(11) Use the labels on the diagram shown in

Figure 9.3.6 to identify the part(s) of Earth

(A, B, C or D) experiencing:

a) summer = C

b) winter = B

c) a day in which the Sun is always in the sky = D

d) a day in which the Sun never appears. = A

Chapter 2.3 page 350

(12) Use Figure 9.3.5 to help to predict the season that Australia experienced on the following dates:

◦A 21 March Autumn

◦B 30 June Winter

◦C New Year’s Day, 1 January Summer

◦D Anzac Day, 25 April Autumn

Chapter 2.3 page 350(13) We can only celebrate New Year’s Eve at 12 midnight because our calendar years are rounded off at either 365 or 366 days. If we used 365.14 days for our calendar year, then New Year’s celebrations would have to be celebrated at different times each year.

a) Calculate how many hours there are in one quarter of a day. One quarter of a day 24/4 =6 hours

b) New Year’s Eve was at 12 am this year. If the calendar year was 365.14 days long, then calculate the time it would occur:

◦ i next year 12am + 6hrs = At 6 a.m.

◦ ii the year after that. 6am + 6am = 12pm (noon)

c) Calculate how many years would pass before NYE returned to 12 am.

Four years would pass. The third year NYE would be at 6pm and the fourth year at 12am

d) Use this example to explain why the length of a calendar year is rounded to 365 or 366 days.

If the year was taken as 365¼ days, each new year would start 6 hours later than the previous year. It would start at midnight only every 4 years.

Chapter Review page 362

(1) State whether the following statements are true or false:

a) Only large masses like planets, stars and moons have a gravitational field.

False: All objects have a gravitational field, but planets, stars and moons have a much greater mass and hence a much larger gravitational field than you or the objects around you.

b) The further you go out from a planet, the weaker its gravity becomes. True

c) A day on Earth is the time it takes for Earth to revolve once around the Sun.

False: A day on Earth is the time it takes for Earth to rotate once around its own axis.

d) Earth has four seasons because of its tilted axis. True

e) On Earth, we only see one side of the Moon. True

f) Pluto is a planet.

False: Pluto is a dwarf planet.

Chapter Review page 362(5) Describe the shape of an ellipse.

An ellipse is an oval or slightly flattened circle

(6) The Moon can still be seen during a lunar eclipse. Explain why?

Some light from the Sun is bent by the Earth’s atmosphere during an eclipse, allowing some light to fall on the Moon. This makes it slightly visible.

(7) Explain why Earth experiences four seasons each year.

The Earth experiences seasons because it is tilted on its axis. Summer occurs in the hemisphere that is tilted towards the Sun, while it is winter in the hemisphere tilted away from the Sun. Spring and autumn occur when the tilt of the Earth towards the Sun is small

(8) Describe how the day and year are related to Earth’s movement.

A day is the time it takes for Earth to rotate once on its own axis. A year is the time it takes to orbit the Sun

Chapter Review page 362(13) Everything around you has its own gravitational field.

a) Identify what mass affects you the most.

The mass that affects you the most is the Earth.

b) Explain why other things like the wall or the person sitting next to you don’t influence you much.

Other things have very little mass and so their gravitational force is very small and won’t have much effect on you.