RI Y3 Physics Notes EOY

Physics Notes (RP) - EOY Topics 1) Measurements -------------------------------------------------- 2-4 2) Kinematics ------------------------------------------------------ 5-6 3) Scalars & Vectors ---------------------------------------------- 7-8 4) Dynamics 1 ---------------------------------------------------- 9-11 5) Dynamics 2 -------------------------------------------------- 11-13 6) Work, Energy & Power ------------------------------------ 14-15 7) EM Spectrum ------------------------------------------------ 16-17 8) Waves --------------------------------------------------------- 18-19 9) Sound -------------------------------------------------------------- 20 10) Pressure ------------------------------------------------------ 21-22 11) Kinetic Model of Matter ----------------------------------- 23-24 12) Temperature ------------------------------------------------ 25-26 13) Thermal Properties of Matter --------------------------- 26-27

2 Measurements 1.1 Accuracy vs. Precision ACCURACY PRECISION Closeness to the actual value Reproducibility Based on a measurement’s true value Not based on a measurement’s true value Can be derived from one reading Has to be derived from multiple readings • Measurement is usually recorded to smallest half division of smallest scale of instrument (e.g. thermometer, measuring cylinder) • When measurements involve intervals, record to smallest division (e.g. metre rule, protractor) 1.2 Units SI DERIVED UNITS Quantity Common units Derived unit Volume m3 m3 Density kg m-3 kg m-3 Acceleration m s-2 m s-2 Force kg m s-2 Newton (N) Work done kg m2 s-2 Joule (J) SI PREFIXES Prefix Symbol Multiply by giga- G x1,000,000,000 mega- M x1,000,000 kilo- k x1,000 deci- d ÷10 centi- c ÷100 milli- m ÷1,000 micro- u ÷1,000,000 nano- n ÷1,000,000,000

3 1.3 S.F & D.P Addition & Subtraction – least decimal place of a term e.g. 0.04529 + 0.0028 = 0.0481 (actual: 0.04809) 5 d.p + 4 d.p = 4 dp Multiplication & Division – least significant figure of a term e.g. 0.93 ÷ 0.07837 = 12 (actual: 11.86678576) 2 s.f ÷ 4 s.f = 2 s.f Combined – find d.p first, then overall s.f e.g. !".!!"!!".!"!".!!"=!.!"!".!!"=0.0007 (1.𝑠.𝑓) 1.4 Measuring Instruments Vernier Calipers • Correct to 0.01cm 10cm + 0.02cm = 10.02cm • When no object is being measured o Lower jaw slightly to left – negative zero error o Lower jaw slightly to right – positive zero error Observed reading – Zero error = Corrected reading e.g. 2.64cm – (-0.02cm) = 2.66cm

4 Micrometer Screw Gauge • Place object between anvil & spindle • Turn ratchet until 2-3 clicks heard o correct pressure o any further turning results in inaccurate reading • Smallest division = 0.01mm • Every horizontal interval is 0.5mm 2.5mm + 0.38mm = 2.88mm • When no object is being measured o Reading < 0 or 0 cannot be seen – Negative zero error o Reading > 0 – Positive zero error • Same method to obtain corrected reading as vernier calipers 1.5 Types of measurement errors Systematic Random > or < true value by fixed amount readings scattered about a mean value; equal chance of (+) & (-) e.g. not accounting for zero error, not accounting for background radiation when measuring activity of radioactive source e.g. fluctuation in count-rate of radioactive decay, variation in diameter of a piece of wire can be eliminated can only be reduced eliminated only if source of error is known, not by repeating measurements & averaging reduced by repeating measurement & averaging, plotting graph & line of best fit

5 Kinematics 2.1 Definitions & Equations v=u+at v2=u2+2as s=ut+!!at2 s=!!(u+v)t QUANTITY DEFINITION SYMBOL Displacement Distance moved in a specified direction from a reference point s Speed Distance travelled / time taken v Velocity Instantaneous Rate of change of displacement with respect to time (found by drawing tangent on s-t graphs) Average Change in displacement / time taken vave Acceleration Instantaneous Rate of change of velocity with respect to time Average Total change in velocity / total time taken aave 2.2 Graphs Displacement-time graphs • Gradient = velocity • Can be negative unlike distance-time a) Velocity = 0 b) Velocity = constant c) Constant acceleration v = final velocity a = acceleration u = initial velocity t = time taken v = final velocity a = acceleration u = initial speed s = displacement s = displacement t = time taken u = initial speed a = acceleration s = displacement v = final velocity u = initial speed t = time taken (aka trapezium area under v-t graph)

6 Velocity-time graphs • Gradient = acceleration • Area = change in displacement • Can be negative unlike speed-time a) Acceleration = 0 b) Acceleration = negative c) Acceleration = po sitive In all cases, because gradient = constant, acceleration = constant Acceleration-time graphs • Area = change in velocity • Can be negative a) velocity = constant b) acceleration = constant 2.3 Sign conventions • For displacement o taken with respect to a reference point § e.g. starting point of motion o if, e.g., displacement to right is positive, then to left is negative • For velocity o Fix a direction of motion as positive § e.g. in vertical motion § if downward motion is fixed as positive, then up is negative o Same case for acceleration

7 Scalars & Vectors SCALARS VECTORS quantities that are fully described by a magnitude alone quantities that are fully described by both a magnitude and a direction (remember using the letters V&S) e.g. distance, speed, time mass, area, volume, energy, work done, and power e.g. displacement, velocity, acceleration, force, weight and momentum 3.1 Addition of Vectors 1. Vector Triangle Method • Connect the tail of V2 to the head of V1 • Everything is to scale (i.e. angles, lengths) • Resultant V joins tail of 1 to head of 2 2. Parallelogram Method • 2 V’s represented by sides of a parallelogram • Resultant V is diagonal Subtraction of vectors • Flip the head & tail of the vector being subtracted Addition of more than 2 vectors • Use a vector polygon • Similar to vector triangle •If both forces in same direction, then Fr = F1 + F2 •If two forces in opposite direction, then Fr = F1 – F2 or F2 – F1, depending on the direction •Hence the addition of two forces (F1 > F2) is: F1 – F2 ≤ Fr ≤ F1 + F2

8 Forces in Equilibrium • When 3 coplanar forces acting on a point are in equilibrium o can be represented in by adjacent sides of triangle o when drawn in a vector triangle, the forces form a closed triangle • Same for polygon of forces 3.3 Vector Resolution • Any vector can be resolved into any two perpendicular directions o Perpendicular components o e.g. horizontal & vertical components • Component of vector = influence of vector in a given direction • Perpendicular components are independent of each other • e.g. Using trigonometry, sin 37° = Fy / 5 Fy = 5 sin 37° = 3.01N cos 37° = Fx / 5 Fx = 5 cos 37° = 3.99N • When object is in equilibrium o Sum of all vertical components of forces = 0 o Sum of all horizontal components of forces = 0

9 Dynamics 1 4.1 Different Types of Forces FORCE DESCRIPTION Weight (W) • Gravitational force exerted by Earth on an object Friction (F) • When 2 surfaces in contact, exert force on each other • Component parallel to surfaces is friction • Acts in a direction so as to resist relative / tendency of motion between the s