UCT OHS Natural Science Grade 8 Term 4 Exam Module 17-30 PDF

Term 4 Examxam Module 17-30 NATURAL SCIENCE Grade 8 Topics you are writing about: Static electricity Electricity and circuits Circuits and components Electromagnets and electric current Series circuit Parallel circuits Radiation of visible light Absorption and reﬂection of visible light The sun and our solar system Objects around the sun Earth and the Milky Way Galaxy The Centauri group of stars Calculating light years The Universe Let’s get started! The outlay of the paper Question 1 10 marks Multiple choice question 01 Example: 1.1 What is NOT part of the water cycle: A. condensation B. evaporation C. sublimation D. deposition Answer: 1.1 A Question 2 10 marks Column A and Column B 02 Example: COLUMN A COLUMN B 2.1 Animals that eat A Primary plants. consumers B Secondary consumers Answer: 2.1 A Question 3 10 marks Give a scientiﬁc term for the 03 statements Example: 3.1 Variables that are kept the same in an experiment. Answer: 3.1 Controlled variables OR ﬁxed variables OR constant variables Question 4-8 60 marks 4-8 Longer questions on all topics Tips: - Ensure you understand circuits, all of the components, how they work, how to draw them and how to do calculations with the components. - Understand how light works, their wavelength, their frequencies and how to do calculations with the speed of light. - Know all things about the sun - Know our solar system and the order of the planets - Know our Universe such as the Milky Way Galaxy and the stars Static Electricity Mod 17 And Electricity and circuit Mod 18 NATURAL SCIENCE Grade 8 DEFINING STATIC ELECTRICITY The effects of static electricity are all around us. Have you ever felt a slight shock when you put a jersey over your head on a cold day, or perhaps you have observed your hair stand on end when you touch certain objects? To understand the above, let’s uncover some important terms. Ref: Drawn on paint Friction A contact forced in which objects are rubbed against each other. Static An imbalance of charges in a non-conducting material, in which the charges electricity remain nearly fixed in one location until they are given a path to escape A contact force in which a charged object is brought in contact to an Conduction uncharged/neutral object. (electric charge can move by 2 objects coming in contact by conduction) A non-contact force in which a charged object is brought Induction close (no contact) to an uncharged object. (electric charge can move by 2 objects coming close by induction) HOW DOES IT HAPPEN? The atom is held together by the electrostatic attraction between the positively charged nucleus and the negatively charged electrons. Within an atom, the electrons closest to the nucleus are the most strongly held, whilst those further away experience a weaker attraction. You have dragged the surface of the plastic comb against the surfaces of your hair. When two surfaces are rubbed together there is friction between them. The friction between two surfaces can cause electrons https://www.siyavula.com/read/science/grade to be transferred from one surface to the other -8 https://www.siyavula.com/read/science/grade-8 ELECTRON TRANSFER AND CALCULATING OVERALL CHARGE https://www.siyavula.com/read/science/grade-8 LET’S CALCULATE THE OVERALL CHARGE OF THE FOLLOWING OBJECTS A B C An image from UCT OHS THE BEHAVIOUR OF CHARGED OBJECTS Objects with the same charge tend to push each other away. We say that they are repelling each other. Objects with opposite charge tend to pull each other together. We say that they are attracting each other. An image from UCT OHS TRANSFER AND DISCHARGE OF ELECTRONS THE SCIENCE BEHIND THE DISCHARGE OF ELECTRONS (SNAP, CRACKLE, SPARK) When electrons transfer from a charged object to a neutral object we say that the charged object has discharged. Pexels Discharging can take place when the objects touch each other or are brought near to each other. When electrons move across an air gap they can heat the air enough to make it glow. The glow is called a spark. Sometimes the air is heated so suddenly, that a sudden expansion of air takes place, causing a snapping/crackling sound. Sparks can be harmless, but sometimes dangerous. (Can cause flammable materials to ignite). Electrostatic discharge can also cause electric shocks. Have you ever been shocked by a shopping trolley while you are pushing it around a shop? You have experienced an electric discharge ! Electrical Discharge There are many examples of static electricity in our everyday lives. Some of these examples include: ○ Clothing - when it is rubbed against surfaces, it causes a build-up of static electricity which can lead to a small shock if you touch a metal object. ○ Electronics - companies have take steps to avoid static electricity damaging their products such as spraying them with an anti-static spray or packaging them in anti-static bags. ○ Chemical industries - chemicals can be flammable and it is important to avoid any sparks from static electricity, so scientists take precautions to avoid this. Electrical Discharge Lightning is an extreme example of static electricity. Lightning is a highly-charged form of static electricity (natural type). The lightning bolts can travel exceptionally fast and reach very high temperatures. These bolts cause a sound when it occurs which is called thunder. Friction in clouds (liquid & ice particles) create a build up of charge. Negative charges collect at the bottom. Negative charges on ground are repelled by clouds negative charge, causing positive charges to line up at ground level. An image from UCT OHS When the size of the charge becomes large enough, the air can no longer resist their flow. Large potential difference. Negative and positive charges flow to meet (electric discharge and the effect of static electricity). Flow of electrons heat the air rapidly. Danger of lightning Objects struck by lightning can catch fire. SAFETY Damaged appliances from power surges Electrocution risk for occupants Go indoors. Avoid water during a storm - dams, lakes, swimming. Avoid metal objects. do not stand under an isolated tree. (they are tall and a better conductor than the air) have the contact numbers for emergency medical and fire services. Wait at least An image 30OHS from UCT minutes after the last thunder roar before going outside. Energy and energy transfer Energy cannot be created nor destroyed, but can be changed from one form to another. Potential energy is the energy stored in an object due to its position/by virtue of its height. Kinetic energy is the energy that an object has due to its motion. When an object starts moving, its potential energy gets converted into An image from UCT OHS learning campus kinetic energy. Energy and energy transfer Ball Calculate the potential energy 10 m 0.5kg of the ball at the given height. Note that gravitational acceleration is 9.8m/s Ep = mgh = 0.5kg x 9.8 x 10m = 49 J. Energy and energy transfer Calculate the potential energy of the ball at the given height. Note that gravitational acceleration is 9.8m/s Ep = mgh = 0.5kg x 9.8 x 0m = 0 J. Ball 0.5kg 0m Systems Systems consist of many different parts all working together to serve a purpose/function. Electrical systems are circuits that consists of different parts that transfers electrical energy. Systems List of parts - ○ Cell: long line and short line with positive and negative side. ○ Light bulb: circle with an ‘x’. Used to convert electrical energy into light and heat. ○ Conducting wire: the pathway that the electrical current passes through. ○ Switch (closed): line with two ‘.’ on either side. A closed switch shows that the electrical current can flow uninterrupted throughout the circuit. Circuit diagrams A simple electric circuit has at least three components: source of energy, such as a battery. conducting material, such as the electric wires Output device that transfers the energy for a useful purpose, such as the bulb that provides light https://www.siyavulaeducation.com/wo rk-oer.html#BOOKS Different Systems Energy systems can be used in different ways to produce, distribute and consume energy. E.g: ○ Mechanical systems ○ Thermal systems ○ Electrical systems Different Systems Mechanical systems: ○ These systems use the energy of movement of objects. ○ These systems rely on the chemical energy from food (in humans) which gets transferred into kinetic energy ○ Chemical potential energy from food eaten (input) → kinetic energy (output). Different Systems Thermal systems: Different Systems Important energy conversions summary ! Mechanical systems: potential energy → kinetic energy Thermal systems: potential energy → heat energy Electrical systems: potential energy → electrical energy Biological systems: potential energy → kinetic energy Current Current is the flow of charge through a conductor. Electrons move through the circuit When electrons flow through the circuit, they move from negative terminal through the conductor, towards the positive terminal - Electron flow Electrons then move from the positive terminal to the negative terminal on the cell - conventional current. Build a circuit & draw its circuit diagram An image from UCT OHS learning campus An image from UCT OHS learning campus Open and Closed Circuits A circuit can only function if there is a complete/unbroken pathway for the electrical charge to flow. LIVE SESSION - Circuits and components NATURAL SCIENCE Grade 8 Circuit components The cell The cell is the source of energy in a circuit. The cell stores electrical potential energy in the form of chemical energy. Wires carry electricity over short and long distances A bulb - an incandescent bulb(an output device). These bulbs have a resistant wire called a filament which is made of wire that resists the flow of electric charges. The filament heats up to be white hot when connected in a circuit and gives off light and heat energy. An LED - device emits light when a current passes through it, making it useful for providing visual feedback. Circuit components A switch controls the flow of current in a circuit. More circuit components A resistor is a device that resists the flow of current in a circuit. Electrical resistance is a measure of how much an object opposes or resists the flow of electric charges. Ohms Fixed and variable resistors. An electric motor is a device that converts electrical energy into mechanical energy. They provide motive power for a variety of devices Buzzers convert electrical energy into sound energy. More circuit components A fuse is an electrical safety device that breaks the circuit if a fault in an appliance causes too much current to flow. too much current flowing, the fuse melts The circuit symbol for a fuse is an '‘s'’ shape. Measuring the current and voltage Current is the flow of charge through a conductor. One ampere of current = flow of one coulomb of electric charge per second through a conductor. A current of 1 ampere, is transferring 1 coulomb of electric charge per second Current is measured in Amperes (SI unit) Ammeter Do you think current would flow if there is a gap in the circuit ? What happens to the current within the bulbs ? Measuring the current and voltage Voltage is the electrical potential difference between two points in a circuit / energy required to move a charge along Voltage is measured in Volts (SI unit) (V) Voltmeter Which circuit component do you think supplies the voltage ? Why? Current and voltage when components change Electromagnets & electric current NATURAL SCIENCE Grade 8 Effects of an electric current Generates heat Resistors allow electrons to move through them, but do not make it easy. They are said to resist the movement of electrons. Resistors therefore influence the electric current in a circuit. But, why would we want to resist the movement of electrons? Resistors can be extremely useful. Think about a kettle. If you look inside you will see a large metal coil. The element is a large resistor. When electrons move through the resistor they expend a lot of energy in overcoming the resistance. This energy is transferred to the surroundings in the form of heat. This heat is useful to us as it heats our water. Effects of an electric current Generates heat cont.. - In an incandescent light bulb, current flows through the thin filament. - Tungsten - High resistance - Electrical energy → heat energy - Glows with heat - Other examples : - Geyser - Heater - Toaster - Kettle Effects of an electric current Generates heat cont.. - Safety: - Faulty appliances like a kettle that boils over if not switched off manually. - Overheating may occur, causing a fire - What is the safety device ? - A fuse serves to protect an overloaded electrical circuit by breaking the flow of electricity before any damage is caused. Effects of an electric current Generates heat cont.. - Safety: Short circuits - Short circuits occur when an easier or shorter electrical path is created. - This path offers little resistance allowing the current to flow through this ‘’short circuit’’ rather than the main circuit path. - Sticking a metal knife into a switched on toaster can create a short circuit ! - Higher current flows through short circuits causing heating up and a fire. Effects of an electric current Effects of an electric current Generates a magnetic field - The movement of current in a wire causes a magnetic field. - Magnetic field - North pole and south pole. Earth has a magnetic field around it. - Attraction and repulsion - A compass has a needle with a small magnet. - Plotting compasses react to magnetic fields. - The plotting compasses change direction when the current is switched on. - This means there is a magnetic field around the wire, which means that the presence of the electric current in the wire must have produced a magnetic field Electromagnets- https://www.youtube.com/watch?v=tHIchO1pbFA Electromagnet: A magnet in which the magnetic field is produced by a current. The magnetic field around an electromagnet can be made stronger by: Increasing the no. of turns of the wire around the nail Increasing the electric current Increasing the voltage https://www.siyavula.com/read/science/grade-8 An image from UCT OHS learning campus Uses of electromagnets speakers electric bells telephones magnetic trains industrial lifters and separators A crane with an electromagnet picking up metal scrap. How would the attracted metal scrap be released from the electromagnet once picked up? Effects of an electric current Causes a chemical reaction in a solution Different ways in which compounds can be split - Thermal decomposition - Electrolysis Uses electrodes We will look at how electricity can be used to separate copper chloride. Watch the video! Thermal decomposition: https://www.youtube.com/watch?v=fwukX8Ec-Pg Electrolysis: https://www.youtube.com/watch?v=38ULHoKWZag Effects of an electric current Causes a chemical reaction in a solution cont.. When copper (II) chloride is placed in water, the copper chloride separates into copper ions and chlorine ions. The copper ions are positively charged & the chlorine ions are negatively charged. Therefore, the mixture of copper chloride and water form an ionic solution. https://www.youtube.com/watch?v=qqmKqpA61GI&t=71s Siyavula Let’s look at how electricity can be used to separate a compound. Name the compound in the solution. What has to be done to allow the electric current to flow through the solution? What is the source of energy ? Copper chloride Crocodile clips needs to be connected. Cells/battery An image from UCT OHS learning campus Uses of electrolysis One of the most important uses of electrolysis is electroplating. Electrolysis is used to electroplate metals. Pixabay Why do we electroplate? An example is in the making of jewellery where an inexpensive metal is made into a ring, for example, and then coated with gold by electroplating. This makes it less expensive than if it were made from pure Gold. Iron rusts easily and so it is useful to coat it with a layer of a zinc to protect it from corrosion. (galvanise) Many car parts, bathroom taps and wheel rims are electroplated with chromium (does not corrode, resists scratches and can be polished for a shiny appearance) Pixabay Wikimedia Series circuits NATURAL SCIENCE Grade 8 Series circuits Definition: In a series circuit all the different components are connected one after the other, without any branches. There is only one pathway for the electric current to follow. An image from UCT OHS learning campus Pixababy Pixabay Pixabay Draw a series circuit Draw a circuit with 3 cells connected in series, 2 bulbs in series and 1 ammeter. Remember to always use symbols when asked to ‘draw’ a circuit. Current at any point in a series Name the component circuit is the same, because that measures the there is only one path for current current in the circuit. to flow. Series circuits Conductors and insulators Conductors : Materials that allow electricity to pass through them Insulators: Materials that don’t allow electricity to pass through them, or they allow very little electricity to pass through them. Good conductors - eg. copper Poor conductors - eg. nichrome Resistance in good conductors are low Resistance in poor conductors are high Common conductors: Copper, Steel, Brass, Aluminium, Nichrome The effects of adding or removing components in a series circuit - Adding/removing cells in a series circuit Cells are the source of energy in a circuit. Voltage in a cell is the energy needed to move a charge, voltage is contained in the cells. Voltage adds up as more cells (voltage) is added in a series circuit. Hence Total voltage = Voltage 1 + Voltage 2 + Voltage 3… Vt = V1 + V2 + V3… In other words, Total voltage is the sum of the voltages of each cell. Vt = V1 + V2 + V3… In other words, Total voltage is the sum of the voltages of each cell. The effects of adding or removing components in a series circuit - Total Voltage in a series circuit is shared amongst the resistors in series Remember, Voltage is the energy used to move a charge Hence, voltage will have an effect on current While current is the rate at which a charge moves. Cells increase, Voltage increases Voltage , Current This can be seen by bulb brightness Current is the same throughout the resistors/bulbs A 1 = A2 = A3 The effects of adding or removing components in a series circuit - Adding / removing resistors/bulbs in series As we add resistors in series, the total resistance increases. An increase in total resistance will decrease the current. Resistance Current Circuit 1 Total Voltage 18V Total Resistance 10 Current: Let’s check on the next slide Circuit 2 Total Voltage 18V Total Resistance 20 Current: Let’s check on the next slide Circuit 1 Total Voltage 18V Total Resistance 10 Current: 1.80 Amps Circuit 2 Total Voltage 18V Total Resistance 20 Current: 0.90 Amps The effects of adding or removing components in a series circuit - Summary Voltage & Current are cells, Voltage (Vt) DIRECTLY PROPORTIONAL !!! Voltage, Current (brighter bulbs). Resistance remains unaffected / independent cells, Voltage. when comparing Voltage to Current Voltage, Current (dimmer bulbs). Resistance & Current are bulbs , Resistance. INVERSELY PROPORTIONAL !!! Resistance, Current (dimmer bulbs). Voltage remains unaffected / independent bulbs, Resistance. when comparing Resistance to Current Resistance, Current (brighter bulbs). LIVE SESSION - Parallel circuits NATURAL SCIENCE Grade 8 Output devices Lets begin with the shorter content on output devices, since parallel circuit understanding will require your continuous chain of thought. Output device: An output device converts or transforms potential energy in a cell into other forms of energy. Explain circuit components in terms of their output. Output devices Eg. LED (Light Emitting Diode): This device emits light when a current passes through it, making it useful for indicating the state of a circuit or for providing visual feedback. A speaker is used to convert electrical signals into sound waves, making it useful for producing audible alerts or for providing feedback in audio applications. Electrical energy —------- > sound energy / waves Parallel circuits Define parallel circuits Bulbs can be connected in parallel. Ammeters are connected in series even in parallel circuits Parallel circuit Vs Series circuit Resistors connected in parallel Let’s discuss the pathway that current takes. Components connected in parallel are connected opposite / across each other on separate branches/wires. Parallel circuits have more than one path for current to flow. If a component is broken or removed, the other parallel branches keep working. Each resistor/bulb gets the full / total voltage to push the charge along. Total Current divides / splits / branches out in a parallel circuit What do ammeters do? If Bulb X was the only resistor in the circuit with a current of 5 amps passing through it, it would be getting the full /total voltage since its the only bulb. When bulb Y is added, it also gets the full voltage and therefore a current of 5 amps as well (if its equal resistance to bulb X). What would therefore be the total current of the circuit ? Which ammeters read the total current ? Which ammeters read the current on :Bulb X Total voltage of a parallel circuit has the :Bulb Y same value as the voltage across each Predict what would happen to the total current if another Bulb (Z) were branch,This relationship can be added in parallel. expressed as: V Total = V1 = V2 … V1 & V2 are across each bulb This can be confirmed using PhET – in the upcoming slides Current divides / splits / branches out in a parallel circuit Parallel circuits can also be drawn like this. Current branching effect is better demonstrated with this diagram Drawing a parallel circuit 1. Can you convert a PhEt constructed circuit into a circuit diagram ? The effects of adding and removing components V Total = V1 = V2 … A Total = A1 + A2 Total current increases as more resistors / bulbs are added because there are more pathways for current to flow Total resistance decreases as more resistors are added (as total resistance total current ) **Let’s conclude that total current splits/branches out. **Total voltage is not shared, it is the same as the voltage across each resistor. The effects of adding and removing components 1. Note the current on the series circuit and on each branch in the parallel circuit. 2. Note the total / circuit current of the parallel circuit. The effects of adding and removing components Total current splits Voltage stays the same More pathways, more current in total /total current Circuit / Total resistance ? At = A1 + A2 + A3 Vt = V1 = V2 Let’s discuss and compare the following.. What happens when a bulb / output component burns out / is disconnected / faulty? 1. Why does the disconnected bulb not shine/work? 2. Why does the connected bulb continue to shine/work? Our home electricals are connected in parallel Let’s summarise current, resistance & voltage in a parallel circuit LIVE SESSION - Radiation of visible light NATURAL SCIENCE Grade 8 Radiation Visible light refers to all forms of radiation we can see with our eyes. ROYGBIV Radiation of light and radiant energy. This energy falls onto Earth in form of light and heat. Radiation Light is produced naturally by the sun or fire or artificially as well using electricity. Luminous and non luminous objects. Chemical reactions also can produce light, eg. lantern fish, glow worms, jellyfish.. Would you consider the moon to be luminescent ? Radiation Light is a form of energy Light energy is also called radiant energy or radiation. Light travels at 300 000 km/s [this is the speed limit of the universe) Light travels in straight lines You can only see, when light from an object enters your eye As you move away from a light source, it’s intensity decreases. Would you be able to see the flower in the middle of darkness? Radiation Spectrum of visible light: the collection of colours that make up white light. The Sun radiates white light, which is a combination of all the different colours we see in a rainbow. Radiation Spectrum of visible light Light travels in straight lines but its movement through a medium causes waves. Wavelength: The length of a wave pattern / distance between 2 points in phase. Frequency: The number of waves that move past a point in one second. Radiation Spectrum of visible light High energy / high Low energy / low frequency / short frequency / long wavelength wavelength UV light has a higher frequency. Protect your eyes and skin from the sun: Apply sunblock Use sunglasses Wear a large brimmed hat Wear higher coverage clothes Dispersion: When white light is broken up into the different colours of light Dispersion: When white light is broken up into the different colours of light The formation of a rainbow The speed of light 300 000 km /s Distance from Earth to the Sun : 150 000 000km Carry out calculations using the speed of light Opaque , transparent & translucent Materials that do not allow light to pass through them. Materials that allow light to fully pass through them (you can see through these objects). Materials that allow light to partially pass through them (you can partially see through these). OPAQUE TRANSLUCENT OPAQUE TRANSPARENT Opaque and transparent objects Factors that influence the size of a shadow : Further distance of light source creates a smaller shadow Closer distance of light source creates a larger shadow. LIVE SESSION - Absorption and reﬂection of visible light NATURAL SCIENCE Grade 8 Visible light overview Using ray diagrams to show the absorption and reﬂection of light - Absorption of light Light can be TRANSMITTED , ABSORBED, REFLECTED OR REFRACTED. Transmission occurs when light hits an object that is transparent or translucent. Some objects that transmit visible light absorb other wavelengths of light. For example, sunglasses are designed to transmit visible light and absorb ultraviolet light, protecting your eyes. Using ray diagrams to show the absorption and reﬂection of light - Absorption of light If all light is absorbed by an object it appears black. If all light is reflected by an object it appears white. A material has colour because it absorbs some of the colours (frequencies) in the visible spectrum of light, and reflects other colours The absorbed colours (frequencies) do not reach the eye, and are not seen. The reflected colours (frequencies) reach the eye, and are seen. Using ray diagrams to show the absorption and reflection of light - Absorption of light We see the red shell of the ladybird as red light is reflected and the other colours are absorbed. What about the black spots of the ladybird? Is black a colour? The black spots on the ladybird absorb all the colours and no light is reflected. Do you remember learning about heat energy transfer in Gr 7? We looked at the absorption & reflection of heat. Using ray diagrams to show the absorption and reflection of light - Absorption of light Using ray diagrams to show the absorption and reﬂection of light - Reﬂection of light On smooth surfaces, all light is reflected in the same direction (regular reflection). On rough surfaces, reflected light is reflected in different directions (scattered reflection). When light is reflected from a rough surface, not all the light that is reflected reaches the eye, and therefore, the brain is not able to form an image. Using ray diagrams to show the absorption and reflection of light - Reflection of light An image from UCT OHS Using ray diagrams to show the absorption and reﬂection of light - Reﬂection of light Ray of light: A line of light that radiates from a luminous object. Ray diagram: A ray diagram shows the path that light travels The law of reflection states that when a ray of light reflects off a smooth surface, the angle of incidence is equal to the angle of reflection Using ray diagrams to show the absorption and reflection of light - Reflection of light Seeing light- The eye The pathway of light → Light passes through the cornea Enters the eye via the pupil (dialate & constricts) Lens Focuses light Light hits/falls onto the retina & where it’s converted into nerve impulses Optic nerve carries nerve impulses to the brain. Brain Forms the image from the nerve impulse. Seeing light- The eye Refraction of light Refraction is the bending of light when it travels from one medium to another. Light behaves as a wave does and waves travel at different speeds in different media. When light enters a different medium, it changes speed, and if it entered at an angle then it also changes direction. Refraction of light When light enters a glass prism or raindrops, at an angle, the white light changes direction causing it to bend. This is the refraction of white light. The refracted white light is made up of colours that travel at different speeds, and so they are refracted / bent at different angles and there they separate or split up into individual colours. This is the dispersion of white light. Red light refracts the least and violet light refracts the most, based on their frequency. Refraction of light Can we explain what is happening with the ruler and straw in the water ? Refraction of light Refraction and reﬂection of light Refraction and reﬂection of light - Refraction Optometrists - specialise in the function and care of eyesight. They help to treat eye diseases and improve the eyesight of their patients. Refraction and reflection of light - Refraction LIVE SESSION - The sun and our solar system NATURAL SCIENCE Grade 8 The sun - as a star Have you ever wondered why the sun is called a star ? Our solar system only has one star, the sun ! It is unique, hence the name Solar. The sun looks bigger and brighter than other stars 150 million km away from earth How come we can see this star in the daytime ? Approx. a million earths could fit in the sun Produces radiant energy - solar radiation Centre of the sun is 15 000 000 C Solar panels The sun - as a star Why is the sun important ? The sun - as a star A. B. C. D. 1. Which of the above scenarios uses the sun's energy ? How do we use it? 2. Differentiate between renewable and non-renewable energy. 3. Which of the above uses renewable energy? 4. Which of the above uses non-renewable energy? The sun - as a star Hottest part of the sun where nuclear reactions occur Dark areas that are slightly cooler than the rest of the Sun's surface,typically 3900 degrees Loops and arcs of gas suspended above the sun’s surface Explosion of gas on the surface which sends high energy particles into space. The sun - as a star Sunspots - Dark areas that are slightly cooler than the rest of the Sun's surface,typically 3900 degrees The sun - as a star What would happen if the sun disappeared ? Earth would be in darkness Planets would continue their forward motion and be thrown out into space What about the moons’ visibility? Photosynthesis? Food chains would be disrupted Freezing temperatures ? Light and heat Collapse of the atmosphere No life sustained :( How the sun works- Nuclear fusion The Sun is mostly made up of hydrogen gas and also helium gas with a tiny amount of other gases. Sun's centre is so hot that nuclear reactions can occur, which change atoms from one element to another! In the Sun's case, four hydrogen nuclei are squeezed or fused together to form a new helium nucleus. This process is called nuclear fusion. This nuclear fusion reaction releases energy because the new helium nuclei produced have slightly less mass than the four hydrogen nuclei used to make them. This energy travels outwards from the Sun's core towards its surface. The Sun's energy then spreads out into the solar system in the form of heat and light. Uranium is used in nuclear power plants. What do you think are the advantages and disadvantages of nuclear power ? The Chernobyl nuclear power plant disaster !!! Maximum severity !!! Ukraine 1986 Lets Watch Sir David Attenborough visit Chernobyl LIVE SESSION - Objects around the sun NATURAL SCIENCE Grade 8 Planets and moons - Overview of the solar system Eight planets around the sun. Incl. moons, dwarf planets, asteroids, kuiper belt objects and comets. Terrestrial planets → Asteroid belt → Gas / ice giants Planet arrangement - MVEMJSUN Watch the planet song ! Acronym for the 8 planets Which is the largest planet? My Very Eager Mother Just Served Us Noodles Mr Vince’s Emotional Monkey Just Sat Under Nelly ? Why was Pluto demoted ? Pluto has not cleared out it’s own orbital pathway. It meets the size requirements of planets (similar size to Mercury) It does orbit the sun. Planets and moons - Overview of the solar system The inner solar system - Terrestrial planets Planets and moons - Overview of the solar system The gas giants - much larger than terrestrial planets Which is the largest planet? Other objects around the sun Asteroids are rocky objects that could be left over from the Most asteroids are found in the formation process of our solar system approx.4.6 billion years ago. asteroid belt, which is between Made of rock and iron ore. Mars and Jupiter. They’re too small to be called planets. An image from UCT OHS https://www.siyavula.com/read/science/grade- learning campus Other objects around the sun Meteoroids - Solid object smaller than an asteroid, mostly from the asteroid belt. Meteor - Is a meteoroid that burns up as it enters earth’s atmosphere / shooting star. Meteorites - The remains of meteors that crash without burning up completely. Comets Comets - icy, dusty objects, orbiting around the Sun at great distances. (rock and ice) - Found in the Kuiper Belt and in the predicted Oort Cloud A comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by another comet. If this happens, then the comet's orbit changes and occasionally the comet will come into the inner solar system for us to see. Comets will travel around the Sun and leave the solar system again. An image from UCT OHS learning campus The Kuiper belt and the Oort cloud The Kuiper belt - a region of space filled with trillions of small icy and rocky objects that lies in the outer reaches of the solar system, past the orbit of Neptune [Eris and Pluto (dwarf planets) lie in the Kuiper belt]. The Oort Cloud - is thought to be a huge cloud of icy objects surrounding the Sun at the very edge of our solar system. (has billions of comets). Oort cloud : Kuiper belt : Circle Circle the Sun in the Sun in the same every direction. plane as planets. An image from UCT OHS learning campus Earth - Earth’s position 3rd planet from the Sun. -40 to 40 degrees celsius average of 15 degrees celsius Perfect distance from the Sun (150 million km) Allows for a perfect temperature range for water to exist in 3 phases. Allows for a perfect temperature range that is comfortable for life to survive in. Habitable zone: The range of distances that a planet can lie from the Sun and still have liquid water on the surface. Our Sun's habitable zone (light green). Our Earth is the only planet in the solar system which is positioned within our Sun's habitable zone. https://www.siyavula.com/read/science/grade-8 LIVE SESSION - Earth and the Milky Way Galaxy NATURAL SCIENCE Grade 8 Conditions that sustain life on earth Outline the factors that sustain life on Earth: 1. Temperature 2. Sunlight 3. Water 4. Oxygen gases Why are these factors important in sustaining life on earth? Conditions that sustain life on earth Temperature : -40 degrees celsius to 40 degrees celsius : Allows water to exist in 3 phases : Habitable temperature range : Organisms are adapted to live in this temperature range Conditions that sustain life on earth Sunlight : Photosynthesis : Trapped in fossil fuels Gases (Oxygen) : Respiration : Used in combustion Conditions that sustain life on earth Water : Water is needed by all organisms to survive. :Plants require water for photosynthesis :Animals depend on plants and need water to survive :Our bodies contain water for many chemical reactions (digestion) :Water is a habitat for aquatic organisms A galaxy is a collection of stars Universe - everything that exists, including galaxies and the spaces between them. (>100 billion galaxies) A galaxy is a massive collection of stars, gas and dust all held together by gravity. All of the individual stars that you can see are members of our Milky Way Galaxy. Ancient greeks thought the galaxy looked like spilled milk. Romans later named it ‘’The Milky Way. Our Milky Way Galaxy This is what the Milky Way would look like if we had to see it from far away in space. But scientists only know this from lots of observations made from Earth. The structure or shape we see is from inference from other observations. https://www.siyavula.com/read/science/grade-8 Galaxies and how we identify them - Galaxy shapes Galaxies have different shapes, to which they can be classified with The most colourful galaxies are called spiral galaxies. Galaxies and how we identify them Our Milky Way galaxy forms part of a larger group of 45 galaxies called the local group. The Milky Way Three main members of the local group : Andromeda Triangulum Andromeda our nearest neighbouring galaxy Spiral Largest Andromeda largest Spiral 2.5 million light years Milky way 2nd largest Barred spiral Triangulum Spiral 3rd largest - Located in a constellation that looks like a triangle UCT OHS Install the star gazer on your phone and map out the night sky LIVE SESSION - The Centauri group of stars NATURAL SCIENCE Grade 8 Rules of engagement 1. Respect your peers and Subject Specialist (no foul or vulgar language or comments to deter from the purpose of the live session will be tolerated). 2. Ask relevant and related questions. 3. Be present and take notes. 4. No numbers or social media handles to be exchanged in the chats. 5. Use emojis to respond, but not to deter from the lesson. 6. If possible keep your camera on. Outcomes: Describe the difference between a galaxy and the universe. Explain the sun's location in the Milky Way galaxy. What to expect today… Our solar system in the Milky Way galaxy The sun’s position in the Milky Way Galaxy Our solar system in the Milky Way galaxy Let’s recap / understand the following: What is a solar system ? What is a galaxy ? What is the Milky Way galaxy ? Constellations A constellation is a group of stars that, when viewed from Earth, form a pattern in the sky. Southern Cross or Crux - famous constellation that is visible, even from big cities in South Africa. Zodiac - derived from the constellations along the sun's path in the sky Uct OHS Questions to answer 1. Can you describe why was our galaxy named the Milky Way ? Ancient greeks thought the galaxy looked like spilled milk. 1. Provide a term for: group of stars that, when viewed from Earth, form a pattern in the sky. Constellation 1. Identify the constellation alongside. The southern cross constellation https://www.siyavula.com/read/science/grade-8 Our solar system in the Milky Way galaxy Articulate the components of the universe and their sizes in comparison to each other. Our solar system is found in a galaxy in the universe. Solar system Galaxy Found in a Galaxy Found in the universe Components include: sun, planets, Components include: stars, asteroids, comets, dwarf planets and dark matter, dust and gas. moons. Much smaller than a galaxy Much bigger than a solar system (contains solar systems) Disc shaped Different shapes and sizes Components of the universe ‘’The Hubble Extreme Deep Field is the most distant picture of the Universe ever taken.’’ The Hubble Telescope was used by astronomers to take an image of a small patch of sky. About 5500 galaxies were discovered in the image. https://www.siyavula.com/read/science/grade-8 The Sun's location in the Milky Way Galaxy Major spiral arms in our galaxy Our Sun is located in a small spiral arm called the Orion (or Local) Arm (toward the edge) Orion (or Local) arm lies between the Sagittarius arm and the Perseus arm. FUN FACT Sun It takes the Sun about 200 million years to complete one orbit around the galaxy centre https://www.siyavula.com/read/science/grade-8 The Sun's location in the Milky Way Galaxy The central lump The rest of the galaxy outside the bulge 100 000 light years or 9.5 x 1017 km https://www.siyavula.com/read/science/grade-8 Questions to answer 1. What are the two main parts that make up our Milky Way Galaxy? The bulge and disk 1. Where are the spiral arms located; in the disk or the bulge of our galaxy ? Disk 3. Label parts A, B & C on the diagram below.. Bulge Sun Disk Uct OHS Solar system Vs Galaxy Vs Universe The Centauri group Which is the closest star to earth ? Next closest star to earth ? Alpha Centauri Describe Alpha Centauri: Triple star system (3 stars are in orbit around each other) Proxima Centauri (small and faint) Contains 3 main stars Centauri A (brightest & big) Centauri B (Bright & big) Can only be seen from the Southern hemisphere (Alpha Centauri is located too far to the south on the sky's dome) Pixabay Proxima Centauri, Centauri A & Centauri B Proxima Centauri, the closest star to our own Sun, is about 40 trillion km away from the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion km away from us. UCT OHS Where is Alpha Centauri located ? Key Broken line : Oort Cloud Number rings: Lightyears https://www.siyavula.com/read/science/grade-8 LIVE SESSION - Calculating light years NATURAL SCIENCE Grade 8 Light years, hours & minutes -What does distance mean to us ? What units do you usually use to measure distance? Which appropriate units of measurement would you use to measure the following distances? 1. Distance from your home to a nearby mall. ____________ 2. DIstance of a short race on a sports field or your backyard. ___________ 3. Length of your desk.__________________ 4. Length of your fingernail. ___________________ 5. Length of a microorganism. ______________ Light years, hours & minutes - How big are the distances in space ? Light years Calculations Light years, hours & minutes - How big are the distances in space ? The immense size of the universe resulted in scientists finding different ways of measuring distance. The Sun is about 150 million kilometres away from Earth. Proxima Centauri, is about 40 trillion kilometres or 4 light years away. All the other solar systems, stars and galaxies are millions, billions and trillions of km away. Using kilometres is impractical because the numbers are far too BIG ! Light years may sound like time , but it is distance. Defining light years as a distance rather than time. Sometimes we also use a unit that sounds like time when we describe distance in our daily lives. What is the speed of light ? 300 000 km /s UCT OHS The Universe NATURAL SCIENCE Grade 8 Facts! 01 Facts Grouping of stars Remember the difference between these terms: Astronomy: The study of celestial bodies Astrology: The branch of science which deals with celestial objects, space, and the physical universe as a whole. Astronomer: A person who is skilled in astronomy or who makes observations of celestial phenomena. Sky view Constellations The sky has been divided up into 88 areas. The ancient names of constellations are still used, for example, Perseus, Centaurus and Orion. The names are related to gods and animals depending on the culture. We see different constellations in summer and winter. Not all can be seen in SA: Winter Spring Summer Fall Scorpius Capricornus Gemini Cancer Sagittarius Aquarius Taurus Leo Aquila Pisces Canis Major Virgo Cygnus Pegasus Cetus Bootes Hercules Eridanus Crater Lyra Orion Hydra Ophiuchus Perseus Telescope -help see faint, distant objects more clearly and magnify the image - Inventor of the telescope Terms: Reﬂection: Bouncing off Refraction: Bending through Magnify: Enlarge Focus: Make clearer Telescope: Magniﬁcation instrument Telescope and conditions for looking into space How does it work: Light emitted from galaxies and stars travel in straight lines in all directions. Looking at a star means you are looking at it’s light rays. The further away a star is, the more the straight is spread out and so we see less of its total light. Telescope gather and direct light from objects so that we can see them better irrespective of the distance. Big lenses or mirrors to collect as much light as possible. Telescope also concentrate or focus the light and redirect it into our small eye so that we can see the dim object. Objective lense Types of telescopes: Optical telescope: collect and direct visible eyepiece light from celestial objects. ○ Reﬂecting: uses mirrors ○ Refracting: uses lenses Magniﬁcation = focal length of telescope ÷ focal length of eyepiece Eg. focal length of telescope is 3 000 mm and the focal length of the eyepiece is 30 mm. magniﬁcation : 3 000 ÷ 30 = 100 times magniﬁcation Types of telescopes: Radio telescope: detects radio waves (not visible to the human eye) coming from distant objects. They have very long wavelengths compared to optical light. Radio telescopes typically look like large dishes. Types of telescopes: Space telescope: Sent into space on rockets where they work as satellites. The telescope on the satellites take pictures of bodies in space without looking through Earth’s atmosphere. They collect other types of light at different wavelengths that we cannot see with our eyes. Best conditions for looking into space: The area is far away from cell phone and radio networks The area has ﬁne weather The area gets little to no rainfall The location has no interference from other radio signals The location is remote/ no towns/ buildings/ developments End.

UCT OHS Natural Science Grade 8 Term 4 Exam Module 17-30 PDF

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