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 Combined 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 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. 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) 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 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. 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)

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