SpaceLesson 1: GravityGravity is a force. It is measured in units called Newtons (N), named after the famous scientist and mathematician Sir Isaac Newton. Gravity, like magnetic and electro-static forces is a non-contact force. That means it can act on you from a distance. You do not have to be touching something to feel its force of gravity. Most forces, such as friction, are contact forces.Gravity is always an attractive force; it pulls objects towards each other.All objects that have energy exert the force of gravity on all other objects with energy. However, the force is very, very weak so you normally only feel the force of gravity from objects that are close and have the largest amount of energy. The mass of an object is directly related to its energy so normally we use mass rather than energy when describing an objects gravity. An object with more mass (more massive) has a stronger gravitational force. Massive does not mean big. An object can be very large but with very little mass, for example a balloon.The size of the force is also related to the distance between the objects; the closer they are the stronger the force of gravity they feel. Standing on the surface of the Earth or other planet you feel the strongest pull of its gravity. As you move away from the surface and into space the pull becomes less.The constant pull of gravity from the Sun, the most massive object in our solar system, causes the planets to move around it in an elliptical (almost circular) path called an orbit.

Mass and WeightMass and weight are not the same thing. It is a common misconception because the two words are used interchangeably in everyday situations. However, in science they have specific meanings that are different.Mass is a measure of the amount of ‘stuff’ something is made of; particles, atoms etc.It is measured in kilograms (kg).It is Constant. It does not change depending on your location.Weight is the force of gravity acting on your mass.It is measured on Newtons (N).It is Not Constant. It does depend on where you are; The Earth, the Moon, in space…Gravitational Field Strength is given in Newtons per Kilogram (N/kg). For Earth this is 9.8N/kg. For planets with more mass than Earth it is higher, for planets with less mass it is lower.

To calculate the weight of an object you use the formula;Weight = Mass x Gravitational Field Strength

78. Use this formula to work out the weight of a 10 kg mass on the surface of the Sun, the planets, the dwarf planets our moon and Ganymede (Jupiter’s largest moon) in the table below;

Star, planet or other object

Gravitational Field Strength / N/kg

Weight / N

The Sun 293

Mercury 3.8

Venus 8.8

Earth 9.8

The Moon 1.7

Mars 3.7

Ceres 0.3

Jupiter 24.7

Saturn 10.5

Uranus 9.0

Neptune 11.7

Pluto 0.5

Eris 0.8

Ganymede 1.4

Lesson 2: Calculations Using w = mg The equation; weight = mass x gravitational field strength can be used to calculate the weight of an object of known mass on any planet, star, asteroid etc. However, the equation can also be rearranged to find any of the variables if two are known.When using equations, we often use symbols instead of words to make it simpler to understand.Weight is given the symbol wMass is given the symbol mGravitational field strength is given the symbol g

So; weight = mass x gravitational field strength becomes w = m x g

For example;

Tom has a mass of 75 kg and is standing on the Moon where the gravitational field strength is 1.7 N/kg. Calculate his weight on the moon.E) Weight = mass x gravitational field strength

V) Mass, m = 75 kg, Gravitational field strength, g = 1.7 N/kg

E) Weight, w = 75 x 1.7

R) w = 127.5

Y) N (Newtons, the unit of weight)

Another example;Tom has a mass of 75 kg but is now on an asteroid that is smaller than the Moon. His weight on the asteroid is 22.5 N. Calculate the gravitational field strength of the asteroid.

E) w = m x g

V) m = 75 kg, w = 22.5 N E) 22.5 = 75 x g R) g = 22.5 / 75

= 0.3

Y) N/kg (Newtons per kilogram)

It is important that the values are given in the correct units when carrying out calculations.Mass must be in kilograms (kg)Weight must be in Newtons (N)Gravitational field strength must be in Newtons per kilogram (N/kg)Sometimes mass is given in grams (g) for very small objects. To convert this to kilograms use the following calculation; Mass in kilograms = Mass in grams / 1000

For example;A toy cars has a mass of 250g so its mass in kilograms is 250 / 1000 = 0.250kg

Sometimes weight is given in kilonewtons (kN) for very large objects. To convert this to Newtons use the following calculation; Weight in Newtons = Weight in kilonewtons x 1000

For example;

A train has a weight of 270 kN so its weight in Newtons is 270 x 1000 = 270,000 N.

Calculate the weight of a 50kg object on the planet Mars where gravitational field strength is 3.7 N/kg

E) Equation – write it out w = m x g

V) Values – write them out, check units w = ? m = 50kg, g = 3.7N/kg

E) Enter values into the equation w = 50 x 3.7

R) Rearrange if necessary & Result w = 185

Y) (Y)units Newtons, N

Calculate the weight of a 30kg object on the planet Saturn where gravitational field strength is 10.5 N/kg

E) Equation – write it out w = …… x ……..

V) Values – write them out, check units w = ? m = ………, g = ………

E) Enter values into the equation w = ……… x ………

R) Rearrange if necessary & Result w = …………

Y) (Y)units …………

Calculate the weight of a 500g object on the planet Venus where gravitational field strength is 8.8 N/kg

E) Equation – write it out

V) Values – write them out, check units

E) Enter values into the equation

R) Rearrange if necessary & Result

Calculate the mass of an object on Uranus, where g = 9.0 N/kg, that weighs 315N

E)

V)

E)

Y) (Y)units

R)

Y)

79. Calculate the weight of 0.1kg apple on earth80. Calculate the weight of a 5kg mass on uranus81. Calculate the mass of an alien that weighs 10N on mars82. The alien flies to Jupiter what happens to its mass?83. Calculate the weight of the alien on Jupiter84. Raphael says “astronauts on the moon can bounce around because there is no

gravity” Is he correct? Give a reason.85. Calculate the weight of a 500kg satellite on earth86. The satellite is launched into deep space, far from any planets and the sun. What

will its mass and weight be?Significant Figures & Decimal PlacesYou may be asked to quote values to a certain number of significant figures or decimal places. Failure to do so can cost you marks in an exam situation.Decimal places refer to the number of characters after the decimal point;34.5467 is to 4 decimal places.When reducing the number of decimal places look at the next number in the sequence and round either up or down based on the following rule;If the number is 5 or larger round up, if less than 5 round down.To 3 decimal places; 34.5467 larger than 5 so… 34.547To 2 decimal places; 34,5467 larger than 5 so… 34.55To 1 decimal place; 34.5467 less than 5 so… 34.5

10. Practice rounding the following numbers to the required number of decimal places;

Original Number Number of decimal places Answer

44.567 1

212.093 1

27.523 1

80.247 1

3.163 1

42.7631 2

56.3471 2

81.1241 2

1001.2358 2

12.34513 3

0.045892 3

10.78291 3

The rules for significant figures are a little more complicated.The numbers 1-9 are always significant.0 is only significant if it is between two significant numbers or at the end of a number after the decimal point.Once you have identified the significant numbers you can then round accordingly as per the rules with decimal places.For example; 0.0000015 has only 2 significant figures as all of the 0’s do not count. But… 0.0001015 has 4 significant figures as the 0 between the 1’s does count. And… 0.00010150 has 5 significant figures as the last 0 also counts.

Another example; 43,250 has 4 significant figuresIf you are required to give it to 3 significant figures, then it becomes 43,300To 2 significant figures it becomes 43,000And to 1 significant figure it would become 40,000

11. In the table below fill in the answer box giving the number to the required significant figures;

Original Number Number of significant figures Answer

27.34 3

0.0002762 3

12.00352 3

240,856 3

150.11 3

72.62 2

0.004821 2

15.32 2

253,200 2

28 1

356 1

0.0083 1

Lesson 3: Days, Years & SeasonsThe Earth is roughly spherical (shaped like a football). It orbits the Sun at the centre of our solar system. Whilst in this orbit it also spins around a central axis like a wheel on an axle. See the diagram below.

The side facing the Sun is in daylight. The side facing away from the Sun is in darkness that we call night. It takes the Earth 24 hours to complete one rotation on its axis. We call that a day.When viewed from above the Earth appears to be spinning in an anticlockwise direction. This means that the Sun always rises in the East, moves across the sky and sets in the West.The other planets in the solar system also have days and nights. The information is given below;

Name of planet/ dwarf planet Time for one rotation on axis/ Earth units

Mercury 59 days

Venus 243 days

Earth 24 hours

Mars 24 hours 37 minutes

Jupiter 9 hours 55 minutes

Saturn 10 hours 40 minutes

Uranus 16 hours 50 minutes

Neptune 16 hours 11 minutes

Pluto 6 days 9 hours

12. Which planet has a day most like the Earths?13. Which planet has the longest day?14. Which planet has the shortest day?15. Based on this information which planet would be the most suitable for humans to

live on?

Orbiting the Sun

All the planets, dwarf planets, asteroids and comets that make up our solar system orbit the Sun. The Sun contains over 99% of the total mass in our solar system and therefore has the strongest pull of gravity. All the planets move around the Sun in the same direction. The time it takes to travel once around the Sun is called the period of revolution. On Earth that is 365.25 days or 1 year.

Information about the other planets is given below;

16. Describe the relationship between Distance from the Sun and Orbital Velocity?17. Describe the relationship between Distance from the Sun and Period of

Revolution?18. Can you explain why this is the case? (Think about the force of gravity before you

answer)

Seasons

On Earth we have seasons. We have summer, where we have longer hours of daylight and it is warmer, and we have winter, where we have fewer hours of daylight and it is colder.

19. Looking at the diagram above what can you say about the Earth that may be the cause of seasons?

20. Why do the Northern and Southern hemispheres not have the same season at the same time?

21. Quito, the capital city of Ecuador is on the equator. Why does it experience very little seasonal change throughout the year?

22. In summer the North Pole has 24 hours of daylight for almost 3 months. Can you explain why?

23. Look at the diagram below;

The diagram shows the position of the Sun in the sky at mid-day on the 21st December.On the diagram draw the path the Sun will take from sunrise to sunset. Draw one arrow on the line to show the direction of travel.

24. Add a second line to show the path taken by the Sun on the 21st June. Show the Sun at mid-day.

25. Explain why the two paths are different?

Lesson 4: The UniverseOur Sun is a star. It is much bigger and brighter than the other stars we see in the sky because it is very much closer than them.A star is the term used to describe a cloud of hydrogen gas that has collapsed under its own gravity to the point that nuclear fusion can occur in its core. This is where atoms are forced together to make larger atoms and, in the process, release huge amounts of energy. This energy is then released into the surroundings as electromagnetic radiation. The balance between these 2 forces causes a star to assume a spherical shape. Our Sun has been doing this for approximately 5 billion years and will continue to do so for at least another 4 billion.

Our solar system is huge in comparison to the distances between places on Earth that we are used to using. Units such as the metre and kilometre are very impractical.

The average distance between the Earth and Sun is 149,600,000,000 m.We call this distance 1 Astronomical Unit (AU).We can use this measurement for comparing distances within the solar system.

Planet Distance from Sun in AU

Mercury 0.39

Venus 0.72

Earth 1.00

Mars 1.52

Jupiter 5.20

Saturn 9.58

Uranus 19.20

Neptune 30.05

The inner rock planets are all relatively close to the Sun. The outer gas giant planets are very much further away. The distances between the outer planets is also huge. This means that most of our solar system is empty space.However, this unit of distance also becomes impractical when we want to measure distance to nearby stars. The next nearest star to Earth is Proxima Centauri. It is 268,770 AU away. For these distances we need a unit of measurement that is even bigger.Light travels at 300,000,000 m/s in empty space.It takes 8 minutes and 18 seconds for light to reach the Earth from the surface of the Sun. For that same light to reach the dwarf planet Pluto takes 5 hours!The unit of measurement we use to measure distance to other stars is called the light year. It is the distance travelled by light in one year.1 light year = 9,460,800,000,000,000 m

Proxima Centauri, our nearest neighbour, is 4.24 light years away from the Earth.Sirius, the brightest star in the sky, is 8.61 light years away from Earth.Betelgeuse, the red star in the top left corner of the constellation Orion is 624.5 light years away.

The Milky Way Galaxy

we are here

There are approximately 250 billion stars in our Galaxy, The Milky Way. It is 105,700 light years in diameter. It is one on of the over 100 billion galaxies that are known in the observable universe.The closest galaxy to the Milky Way is the Andromeda Galaxy which is 2.5 million light years away.

Time TravelWhen we look at light coming from another star, we are seeing that star as it was in the past. The light we see today coming from Proxima Centauri left that star over 4 years ago. The light coming from Betelgeuse left that star 642 years ago. When we look at the light from distant galaxies we are looking at them as they were before the time of the dinosaurs.

26. Put the following words in order of size from smallest to largest:Planet, galaxy, universe, solar system, star

27. What is the relationship between the distance a planet is from the sun and the length of its year.

28. What defines a day?29. What defines a year?30. Why is mars’ gravity lower than earths?31. What is a largest distance 1 light year, 500AU or 9million KM