P2 Science Friday 15th June 2018 Key Revision

P2  Science Friday 15th June 2018 Key Revision

P2 Science Friday 15th June 2018 Key Revision Points Triple Science Forces & Weight Vector magnitude and direction (i) displacement (ii) velocity (iii) i) displacement (i) displacement (ii) velocity (iii) ii) velocity (i) displacement (ii) velocity (iii) iii) acceleration (i) displacement (ii) velocity (iii) iv) force (i) displacement (ii) velocity (iii) v) weight (i) displacement (ii) velocity (iii) vi) momentum Scalar magnitude ONLY (i) displacement (ii) velocity (iii) i) distance (i) displacement (ii) velocity (iii) ii) speed (i) displacement (ii) velocity (iii) iii) time (i) displacement (ii) velocity (iii) iv) power (i) displacement (ii) velocity (iii) v) energy Contact force physically touching (i) displacement (ii) velocity (iii) i) friction (i) displacement (ii) velocity (iii) ii) air resistance (i) displacement (ii) velocity (iii) iii) tension (i) displacement (ii) velocity (iii) iv) normal contact force Non-contact force physically separated (i) displacement (ii) velocity (iii) i) gravitational (i) displacement (ii) velocity (iii) ii) electrostatic (i) displacement (ii) velocity (iii) iii) magnetic

Write down the equation that links mass, gravitational field strength and weight. [REMEMBER] The weight of an object may be considered to act at a single point referred to as the objects centre of mass Resultant Forces Resultant Force Is a single force that has the same effect as all the original forces acting together HT ONLY Need to draw free-body diagrams (i) displacement (ii) velocity (iii) examples below)

For these diagrams you do not need to draw the actual object a dot/square can represent the object and simple arrows represent the magnitude and direction Vector Diagrams Forces (i) displacement (ii) velocity (iii) HT Only) Example. A woman walks 40m east then 30m south What is the resultant displacement (i) displacement (ii) velocity (iii) you have to draw a scaled Diagram see the one below) Work Done Work Done When a force is used to move an object, energy is transferred (i) displacement (ii) velocity (iii) because the object has moved)

Write down the equation that links distance, force and work done.[REMEMBER] 1 joule = 1 newton-metre Now we can combine two equations that you have to memorise. Question In this question we have MASS not WEIGHT so two steps use W = m x g Elasticity 1. Compression forces Squeezing or crushing a drink-can two forces are involved, acting inwards onto the object 2. Tension forces Stretching a blob of blu-tac or a rubber band two forces are involved, acting outwards from the object

3. Bending forces Bending a plastic ruler two forces are involved, acting inwards very much like the compression forces, but having the result of bending the object. 4. Elastic deformation When we stretch a rubber band or a spring a small amount we temporarily deform it. The object will return to its original size once the deforming force is removed. 5. Inelastic deformation when we squash a drink-can or stretch a piece of blu-tac, we permanently deform it. The object will not return to its original size once the deforming force is removed. Extension of spring RP 6 XP IV: Mass (i) displacement (ii) velocity (iii) 1N additions) DV: Extension of spring CV: (i) displacement (ii) velocity (iii) i) Spring (i) displacement (ii) velocity (iii) ii) the point of measuring the

extension (i) displacement (ii) velocity (iii) start-end) (i) displacement (ii) velocity (iii) iii) waiting for spring to Stop bouncing/moving Write down the equation that links extension, force applied to a spring and spring constant.[REMEMBER] Elastic PE & Extension If one keeps adding masses to the spring the proportional relationship between force and extension breaks down called the limit of proportionality (i) displacement (ii) velocity (iii) before this limit = linear; after this limit = non-linear). The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

You do not need to Remember this equation Just use it Moments & Gears (i) displacement (ii) velocity (iii) Triple Only) Examples of forces causing rotation Write down the equation that links distance, force and moment of a force. [REMEMBER] In balancing moments: clockwise = anticlockwise Examples of GEARS

Pressure in Fluids (i) displacement (ii) velocity (iii) Triple Only) Write down the equation that links area of the surface, force normal to a surface and pressure.[REMEMBER] (ALL) On equation sheet (HT ONLY) (HT ONLY) The greater the depth the greater the pressure. The greater the density the greater the pressure. The greater the gravitational field strength the greater the pressure. Floating/Sinking & Atmospheric Pressure (HT ONLY) Floating & Sinking

UPTHRUST A partially submerged object experiences a greater pressure on the bottom surface than on the top surface (i) displacement (ii) velocity (iii) resultant force upwards) If the UPTHRUST is GREATER than the weight of the object the object will RISE up through the liquid. If the UPTHURST is LESS than the weight of the object the object will SINK. If the UPTHRUST force is EQUAL to the weight of the object the object will FLOAT (i) displacement (ii) velocity (iii) not move). Atmospheric Pressure ALL Tiers Earth atmosphere model think layer of air round the earth atmosphere gets less dense with increasing altitude (i) displacement (ii) velocity (iii) height) Why? (explain) air molecules colliding with surface create atmospheric pressure as the altitude increases so the number of particles decrease (i) displacement (ii) velocity (iii) less air) so therefore there are less collisions so less pressure So

atmospheric pressure decrease s with an increase in height Distance/Displacement & Speed Distance & Displacement Distance how far an object moves Scalar direction does not matter Displacement includes both distance in straight line and direction Vector Speed Scalar (therefore Velocity is Vector) Walking = 1.5m/s Running = 3m/s Cycling = 6m/s Speed of sound = 330m/s in air Write down the equation that links distance travelled, speed and time. [REMEMBER] Please be careful you can write speed = distance/time that is fine but if use shorthand DO NOT WRITE s=d/t use the one above instead

(HT ONLY) motion in a circle requires changing velocity but constant speed because direction (i) displacement (ii) velocity (iii) if tangent is drawn) is always changing to maintain speed (i) displacement (ii) velocity (iii) constant acceleration). Distance Time Graphs 1. Calculate Speed gradient of d-t graph 2. (HT ONLY) Calculate Acceleration at given point (i) displacement (ii) velocity (iii) time) draw a tangent (i) displacement (ii) velocity (iii) then triangle) then work out gradient (i) displacement (ii) velocity (iii) y/x) Different combinations or lines for D-T graphs below.. Velocity Time Graphs & Acceleration 1. Calculate Acceleration gradient of v-t graph

2. (HT ONLY) Calculate distance/displacement area under the line Different combinations or lines for V-T graphs below.. Write down the equation that links acceleration, change in velocity and time taken. [REMEMBER] Acceleration & Terminal Velocity On equation sheet - Uniform Acceleration (constant acceleration) Object falling under gravity has an acceleration of 9.8m/s Be careful that one of the velocities might be 0, read the Q! especially if from a standing start etc. or it stops dead. Terminal Velocity An object falling through a fluid (i) displacement (ii) velocity (iii) gas/liquid) initially

accelerates due to the force of Gravity Eventually the resultant force will be zero and the object will move at its terminal velocity. TRIPLE ONLY Terminal Velocity Drag (UP) Weight (Down) 1: Newtons First Law 3 Newtonian Laws If the resultant force acting on an object is zero (i) displacement (ii) velocity (iii) i) the object is stationary, the object remains stationary (i) displacement (ii) velocity (iii) ii) the object is moving, the object continues to move at the same speed and in the same direction same velocity

(HT ONLY) these two circumstances is called INERTIA 2: Newtons Second Law (f=ma) The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object. Write down the equation that links acceleration, mass and resultant force. [REMEMBER] (HT ONLY) Inertial mass measure of how difficult it is to change the velocity of an object defined as ratio of force: acceleration 3: Newtons Third Law Whenever two objects interact, the forces they exert on each

other are equal and opposite. Examples Acceleration XP RP 7 Investigating effect of mass on acceleration (at constant force) 1. Set up apparatus as shown on diagram with 1kg mass on the trolley (i) displacement (ii) velocity (iii) blu-tac) string should touch ground 2. Place 1N (i) displacement (ii) velocity (iii) 100g) onto mass holder at the end of string 3. Make sure the card segment attaches passes through the light gate and interrupts the light beam measure width and enter data in data logger 4. Make sure you release the trolley from the same distance from the gate and record acceleration 5. Repeat steps 2-4 by adding 1N to the mass holder

Investigating effect of force on acceleration (at constant mass) Exactly the same experiment set up BUT now increase the mass ON the car and keep the mass on the end of the string the SAME Errors: (i) displacement (ii) velocity (iii) i) trolleys have differing masses (i) displacement (ii) velocity (iii) ii) different mass of blu-tac (i) displacement (ii) velocity (iii) iii) string different materials relates to friction (i) displacement (ii) velocity (iii) iv) length of card segment not measured or different in each experiment (i) displacement (ii) velocity (iii) v) not starting/letting go of trolley at the same point (i) displacement (ii) velocity (iii) distance) Do not get forget the classic ramp acceleration practical too (increase ramp therefore increase acceleration) Forces & Braking Stopping distance = thinking distance (reaction time) + braking distance The distance is to do with DISTANCE it takes to do something NOT THE TIME it takes!! Thinking distance increases

(i) displacement (ii) velocity (iii) i) Alcohol (i) displacement (ii) velocity (iii) ii) drugs (i) displacement (ii) velocity (iii) iii) tiredness (i) displacement (ii) velocity (iii) iv) Distractions (i) displacement (ii) velocity (iii) reaction 0.2-0.9s) Use computer programmes to Measure reaction times greater precision Braking distance increases (i) displacement (ii) velocity (iii) ii) brakes/tyres are worn (i) displacement (ii) velocity (iii) ii) poor weather conditions (i) displacement (ii) velocity (iii) icy/wet road) (i) displacement (ii) velocity (iii) iii) increase mass in car (i) displacement (ii) velocity (iii) i.e. more passengers) (i) displacement (ii) velocity (iii) iv) speed Brakes when force is applied to brakes work done by friction force between brakes and wheel reduces KE of the vehicle slowing it down but the temp. of brakes increase Large decelerations can lead to loss of control lack of grip skidding or overheating brakes Momentum (i) displacement (ii) velocity (iii) HT Only)

Write down the equation that links mass, momentum and velocity. [REMEMBER] Conservation of momentum the total momentum before an event is equal to the total momentum after the event. (TRIPLE & HT ONLY) Calculations for momentum collisions remember MOMENTUM BEFORE = MOMENTUM AFTER (i) displacement (ii) velocity (iii) and anything that is stationary has a velocity = 0) (TRIPLE & HT ONLY) Changes in momentum This equation is given on equation sheet This equation relates to safety features i.e. air bags, seat belts, crumple zones. gymnasium crashmats, cycle helmets, cushioned surfaces for playgrounds etc. In most of these it is the TIME for the collisions to take place that increases NOT, less force per se, by increasing the time taken you

decrease the force and then momentum etc. Waves Longitudinal vibrations are along the same direction as the direction of travel areas of compression and rarefaction sound waves Transverse the vibrations are at right angles to the direction of travel water waves & EM spectrum Properties of waves Amplitude maximum displacement of a point on a wave away from its undisturbed position.

Transverse distance from a point on one wave to the equivalent point on the adjacent wave. Frequency is the number of waves passing a point each second. On equation sheet Wave speed = speed at which the energy is transferred through the medium Wave Equation & RP XP 8 - Waves Write down the equation that links frequency, wavelength and wave speed. [REMEMBER] (i) displacement (ii) velocity (iii) i) describe a method to measure the speed of sound waves in air 1. Person A stands as far away as possible from a large reflecting wall

2. And claps their hands rapidly at a regular rate. 3. This rate is adjusted until each clap just coincides with the return of an echo of the previous one or until clap and echo are heard as equally spaced. 4. Use a stopwatch to find the time between claps, t. 5. Make a rough measurement of distance to the wall, s. 6. The speed of sound, v = 2s/t in the first case. RP8 Waves RP XP 8 (i) displacement (ii) velocity (iii) ii) (i) displacement (ii) velocity (iii) ii) describe a method to measure the speed of ripples on a water Surface (i) displacement (ii) velocity (iii) need stopwatch, ruler, ripple tank see diagram) 1. Set up the ripple tank with about 5 cm depth of water. 2. Height of the wooden rod should JUST touch the surface of the water. 3. Switch lamp and motor on to low frequency waves that can be clearly

observed. 4. Measure the length of a number of waves then divide by the number of waves to calculate the wavelength. It may be more practical to take a photograph of the card with the ruler and take your measurements from the still picture. 5. Count the number of waves passing a point in ten seconds then divide by ten to record frequency. 6. Calculate the speed of the waves using: wave speed = frequency wavelength. RP8 Reflection RP XP 9 (i) displacement (ii) velocity (iii) Triple Only) Reflection waves can be reflected at the boundary between 2 different

mediums Examples of absorption of wave energy 1. waves hitting the beach usually give most of their energy to the sand 2. sunlight landing on a face is mostly absorbed, warming the skin 3. sound waves hitting thick curtains give up their energy and the sound is muffled Examples of transmission of wave energy 1. sea waves passing a shallow area continue with their energy mostly unchanged 2. light passing through a glass window continues with over 95% of its energy 3. ultrasound waves scanning a baby pass from flesh into bone and continue

with enough energy for the machine to detect the echo RP8 Refraction RP XP 9 (i) displacement (ii) velocity (iii) Triple Only) Refraction (i) displacement (ii) velocity (iii) HT Only) Refraction (i) displacement (ii) velocity (iii) i) If the ray moves from a LESS to a MORE dense medium then the ray bends TOWARDS the normal because light travels more slowly (i) displacement (ii) velocity (iii) i.e. Air water) (i) displacement (ii) velocity (iii) ii) If the ray moves from a MORE to a LESS dense medium then the ray bends AWAY from the normal

because light travels quicker (i) displacement (ii) velocity (iii) i.e. Water Air) Examples of Wave front diagrams (i) displacement (ii) velocity (iii) HT Only) Sound Waves (i) displacement (ii) velocity (iii) Triple & HT Only) Sound waves vibrations can travel through solid Ear sound waves cause ear drum to vibrate through a series of compressions conversion of sound waves to vibration of solids works on limited frequency The denser the object quicker sound travels because particles are closer together Human hearing is from 20Hz to 20kHz

Detection/Exploration Waves (i) displacement (ii) velocity (iii) Triple & HT Only) Ultrasound have a higher frequency than human hearing partially reflected when they meet a boundary between 2 different media time taken to each detector determines the boundary medial and industrial imaging Seismic Waves produced by earthquakes provide evidence for structure/size of Earths core (i) displacement (ii) velocity (iii) i) P-waves (i) displacement (ii) velocity (iii) longitudinal) travel at different speeds through solids and liquids (i) displacement (ii) velocity (iii) ii) S-waves (i) displacement (ii) velocity (iii) transverse) cant travel through liquids Echo Sounding using high frequency sound waves is used to detect objects in deep water

EM Spectrum EM Spectrum are transverse waves continuous spectrum travel same velocity through a vacuum 1. radio waves television and radio 2. microwaves satellite communications, cooking food 3. infrared electrical heaters, cooking food, infrared cameras 4. visible light fibre optic communications 5. ultraviolet energy efficient lamps, sun tanning 6. X-rays and gamma rays medical imaging and treatments. EM Spectrum - Properties 1. (i) displacement (ii) velocity (iii) HT ONLY) Radio waves produced by oscillations in electrical circuits when absorbed they create AC

current with same frequency as wave so they in turn can induce oscillations in electrical circuit 2. Changes in atoms/nuclei gamma rays 3. UV, X-Rays and Gamma Rays hazardous to body tissue depends on (i) displacement (ii) velocity (iii) i) dose (i) displacement (ii) velocity (iii) ii) type of radiation measure radiation in Sieverts (i) displacement (ii) velocity (iii) Sv) 4. UV (i) displacement (ii) velocity (iii) i) cause skin to age prematurely (i) displacement (ii) velocity (iii) ii) increase risk of skin cancer 5. X and Gamma Rays ionising radiation mutations in genes Lenses (i) displacement (ii) velocity (iii) Triple Only) Principal Focus parallel rays of light are brought to a focus

Focal Length distance from the lens to the principal focus CONVEX LENS at various points Visible Light (i) displacement (ii) velocity (iii) Triple Only) Each colour of VL has own wavelength/ frequency Specular reflection reflection from a smooth surface in a singular direction Diffuse reflection reflection from a rough surface causing scattering Colour Filters absorb certain wavelengths and transmit other wavelengths (i) displacement (ii) velocity (iii) remember any colour will absorb ALL

colours but the colour/s it is made from) Opaque object determined by which wavelengths are strongly reflected wavelengths not reflected are absolved if all reflected equally white if all absorbed appears black IR Absorption & Emission RP XP 10 Method 1. Place the Leslie cube on to a heat proof mat. 2. Fill the cube with very hot water and replace the lid of the cube. 3.Use the detector to measure the amount of infrared radiated from each surface.

4.(i) displacement (ii) velocity (iii) CV) Make sure that before a reading is taken the detector is the same distance from each surface. 5.Draw a bar chart to show the amount of infrared radiated against the type of surface. Remember the Leslie Cube has 4 different surfaces have a look at diagram therefore you do not need to do the experiment with different insulating layers all the surfaces have same surface area (i) displacement (ii) velocity (iii) CV) and they all start with the temperature (i) displacement (ii) velocity (iii) CV) hence the Cube is very useful in making sure the control variables are consistent. Black Body Radiation (i) displacement (ii) velocity (iii) Triple Only) All objects emit and absorb infra-red radiation the hotter the body more IR radiates in a given time A perfect black object absorbs all the radiation incident on it no reflection

or transmission of radiation but therefore because it is the best absorber it is also a good emitter. The temperature of a body increases if rate of absorption is higher than rate of emission (HT ONLY) Greenhouse effect & greenhouse are examples of absorption and radiation being emitted and used (i) displacement (ii) velocity (iii) difference in type of waves) Poles of a Magnet Magnetic forces are strongest at the poles Two like poles = REPEL & 2 unlike poles = ATTRACT both non-contact force Permanent magnet (i) displacement (ii) velocity (iii) Fe, Ni, Co, Steel) produces its own magnetic field Induced magnet a material that becomes a magnet when in a magnetic field Magnetic field region around the magnet where a force acts upon another magnet Attraction of magnetic field depends on the distance from the magnet closer to the poles the stronger the mag. Field

Magnetic field lines FROM NORTH TO SOUTH! Magnetic compass contains small bar magnet needle points in direction of Earth's magnetic field Electromagnetism When a current flows through a conducting wire magnetic field produced strength of the field depends (i) displacement (ii) velocity (iii) i) current through the wire (i) displacement (ii) velocity (iii) ii) distance from the wire SOLENOID shaping wire (i) displacement (ii) velocity (iii) twisting/coiling) increases the strength of magnetic field it is strong and uniform. SOLENOID Cross-section through solenoid You can FURTHER increase the strength of the magnetic field by placing bar magnet (i) displacement (ii) velocity (iii) iron) within the coil this is an ELECTROMAGNET How can the magnetic effect of a current can be demonstrated

Make a simple electric circuit by joining a long straight wire with a battery and a plug. Now, take a magnetic compass needle and place the straight wire parallel and over the compass needle. Then switch on the circuit so that current flows through the wire from south to north directions. Now, you will found that the north pole of compass needle gets deflected towards the west. Flemings LHR (i) displacement (ii) velocity (iii) HT Only) MOTOR EFFECT when a conductor carrying a current is placed in a magnetic field the magnet and the conductor exert a force on each other Flemings LHR enables you to work out: (i) displacement (ii) velocity (iii) i) magnetic force (i) displacement (ii) velocity (iii) motion) (i) displacement (ii) velocity (iii) ii) Magnetic field (i) displacement (ii) velocity (iii) NS) (i) displacement (ii) velocity (iii) iii) Current (i) displacement (ii) velocity (iii) from +ve to ve) Examples are below as to how to use it!

The factors the affect the size of the force on the conductor: (i) displacement (ii) velocity (iii) 1) size of current (i) displacement (ii) velocity (iii) ii) strength of magnetic field bigger magnet For a conductor at right angles to a magnetic field and carrying a current On equation sheet Electric Motors (i) displacement (ii) velocity (iii) HT Only) ELECTRIC MOTOR When a coil of wire carrying a current in a magnetic field rotates see 3 different versions of the same diagram so you are familiar with it Explanation of electric motor: When an electric current flows through a coil coil experiences a force and moves one side moves up the other down the direction of current must be reversed every half tern this is done by a commutator (i) displacement (ii) velocity (iii) conducting ring split in 2) Increasing the motor effect

(i) displacement (ii) velocity (iii) i) Increase the current (i) displacement (ii) velocity (iii) ii) Increase the strength of magnetic field (i) displacement (ii) velocity (iii) iii) Place commutator closer to wire Btw if you want to change direction either (i) flip over the magnets (ii) change the direction of current (flip battery other way around) Loudspeakers (i) displacement (ii) velocity (iii) Triple & HT Only) Loudspeakers transform electrical signals into sound. Inside a loudspeaker there is a permanent magnet. An electromagnet attached to the speaker cone is inside the magnet field of the permanent magnet. Explanation of loudspeakers 1. The electrical current from the amplifier is

continually changing direction 2. Causes the magnetic field around the electromagnet to continually change. 3. The changing attraction and repulsion between both magnetic fields make the electromagnet move back and forth. 4. This causes the speaker cone to vibrate back and forth, which generates sound waves. 5. The frequency at which the current changes direction is the frequency of the sound that the speaker produces. Induced Potential (i) displacement (ii) velocity (iii) Triple & HT Only) Generator Effect electrical conductor moves relative to a magnetic field a p.d. is induced across the ends of the conductor if conductor is part of a complete circuit a current is induced

An induced current generates a magnetic field that opposes the original change, either the movement of the conductor or the change in m magnetic field. Factors affecting the induced potential (increase) (i) displacement (ii) velocity (iii) i) The speed of movement is increased (i) displacement (ii) velocity (iii) ii) The magnetic field strength is increased (i) displacement (ii) velocity (iii) iii) The number of turns on the coil is increased (i) displacement (ii) velocity (iii) iv) Having an iron core inside the coil Factors that affect the direction of the induced potential difference/induced current (i) displacement (ii) velocity (iii) i) The magnet is moved out of the coil (i) displacement (ii) velocity (iii) ii) The other pole of the magnet is moved into the coil Generator & Microphones (i) displacement (ii) velocity (iii) Triple & HT Only)

Making AC Electricity When a wire is moved in the magnetic field of a generator, the movement, magnetic field and current are all at right angles to each other. If the wire is moved in the opposite direction, the induced current also moves in the opposite direction. This means that as a coil is rotated in a magnetic field, the induced current reverses direction every half turn. This is called alternating current (i) displacement (ii) velocity (iii) AC). It is different from the direct current (i) displacement (ii) velocity (iii) DC) produced by a battery, which is always in the same direction. Microphones 6-Marker 1. pressure variations in sound waves cause the flexible diaphragm to vibrate 2. the vibrations of the diaphragm cause vibrations in the coil 3. the coil moves relative to a permanent magnet, so a potential

difference is induced in the coil 4. the coil is part of a complete circuit, so the induced potential difference causes a current in the circuit 5. the changing size and direction of the induced current matches the vibrations of the coil 6. the electrical signals generated match the pressure variations in the sound waves Transformers (i) displacement (ii) velocity (iii) Triple & HT Only) Transformer made from primary and secondary coil with iron core On equation sheet If 100% efficient the electrical power put and input would be equal therefore.

(EXPLAIN) How the effect of an AC current in one coil in inducing a current in another is used in transformers 1. The primary coil is connected to an AC supply 2. An alternating current passes through a primary coil wrapped around a soft iron core 3. The changing current produces a changing magnetic field 4. This induces an alternating voltage in the secondary coil 5. This induces an alternating current (i) displacement (ii) velocity (iii) AC) in the circuit connected to the secondary coil Solar System (i) displacement (ii) velocity (iii) Triple Only) Solar system (i) displacement (ii) velocity (iii) i) 1 star (i) displacement (ii) velocity (iii) sun) 8 planets and dwarf planets orbit around the sun (i) displacement (ii) velocity (iii) ii) natural satellites and moons orbit around planets (i) displacement (ii) velocity (iii) iii)

the solar system is part of the Milky Way galaxy Formation of the Sun (i) displacement (ii) velocity (iii) i) formed from a cloud of dust and gas (i) displacement (ii) velocity (iii) nebula) and (i) displacement (ii) velocity (iii) ii) pulled together by gravitational attraction Protostar As the gas falls together, it gets hot A star forms when it is hot enough for nuclear fusion reactions to start. This releases energy, and keeps the star hot. Main Sequence Star a star is stable because the forces in it are balanced The outward pressure from the expanding hot gases is balanced by the force of the stars gravity. E.g. our Sun is at this stable phase in its life. Nuclear fusion involves two atomic nuclei joining to make a large nucleus. Energy is released when

this happens. Life cycle of a star (i) displacement (ii) velocity (iii) Triple Only) During most of a star's lifetime, hydrogen nuclei fuse together to form helium nuclei. As the star runs out of hydrogen, other fusion reactions take place forming the nuclei of other elements. Heavier elements than hydrogen and helium (i) displacement (ii) velocity (iii) up to iron) are formed. Elements heavier than iron are formed in supernovas. (i) displacement (ii) velocity (iii) i) Fusion processes in stars produce all of the naturally occurring elements. (i) displacement (ii) velocity (iii) ii) Elements heavier than iron are produced in a supernova. The explosion of a massive star (i) displacement (ii) velocity (iii) supernova) distributes the elements

throughout the universe. Heavy elements are found in the Sun and planets of the solar system. This suggests that the solar system was formed from the remains of earlier stars that exploded as supernovas Orbital Motion (i) displacement (ii) velocity (iii) Triple Only) Gravity provides the force that allows planets and satellites (i) displacement (ii) velocity (iii) both natural and artificial) to maintain their circular orbits. An object moving in a circle is constantly changing direction. This means that, even if its speed stays the same, its velocity is constantly changing. (i) displacement (ii) velocity (iii) Remember that velocity is speed in a particular direction.)

If the objects velocity is changing, it must be accelerating. The centripetal force is the resultant force that causes this acceleration, and it is always directed towards the centre of the circle. Changing Speed An object travelling faster covers more distance per second. It will change direction by a bigger angle each second compared to slower object. A greater centripetal force is needed to achieve this bigger acceleration toward the centre. Changing Radius A circle with a smaller radius has a smaller circumference. Therefore, an object travelling in a circle with a smaller radius has less distance to travel per orbit. It will complete more of the orbit per second, changing direction by a greater angle each second. A greater centripetal force is needed to achieve this bigger acceleration toward the centre.

Red Shift (i) displacement (ii) velocity (iii) Triple Only) Red Shift The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. (i) displacement (ii) velocity (iii) observed light coming from galaxies) this provides evidence for Big Bang Theory. BBT suggests that the universe began from a small region that was extremely hot and dense Since 1998 the most distant galaxies are receding faster However there is still much about the universe not understood dark mass/dark matter The diagrams below how you evidence red shift you can see that the black lines have shifted to the red end means galaxies moving away however if they move to the blue end the galaxies are moving towards each other! (i) displacement (ii) velocity (iii) this is blue shift)

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