(NHHS) Pure Physics Notes/Summary

guan studies 🤓 MEASUREMENTS term definition physical quantity a quantity that can be measured. it consists of a numerical magnitude and a unit oscillation each complete to-and-fro motion period time taken for one complete oscillation factors : length of string, gravitational field strength scalar quantity a physical quantity that has magnitude but no direction (e.g. mass, distance, speed, quantity) vector quantity a physical quantity that has both magnitude and direction (e.g. force, displacement, velocity, acceleration) base quantities SI unit symbol for si unit length metre m mass kilogram kg time second s electric current ampere A thermodynamic pressure kelvin K amount of substance mole mol luminous intensity candela cd factor prefix symbol

10 12 tera- T 10 9 giga- G 10 6 mega- M 10 3 kilo- k 10 -1 deci- d 10 -2 centi- c 10 -3 milli- m 10 -6 micro- µ 10 -9 nano- n object measurement hydrogen nucleus radius: 10 -15 m ‼ typical atom diameter: 1.0×10 -10 m ‼ human hair diameter: 0.1µm wire diameter: 2×10 -3 m chopsticks length: 2×10 -1 m football field length: 10 2 m mount everest height: 8×10 3 m ‼ earth diameter: 10Mm light distance travelled in a year: 9.5×10 15 m earth to the andromeda galaxy distance: 2×10 22 m digital calipers: part use inside jaws used to measure the internal diameter of objects outside jaws used to measure the external diameter or width of objects

digital display used to show the numerical value locking screw used to ensure that the jaws do not move apart zero button used to reset the displayed length back to zero tail used to measure the depth of an object digital micrometer screw gauge: part uses anvil & spindle used to measure the diameter of an object digital display used to show the numerical value zero button used to reset the displayed length back to zero ratchet can be turned to adjust the spindle so that the spindle is in contact with the object instrument precisions: instrument measuring range smallest division example of usage measuring tape zero to several metres 0.1cm a person’s waist metre rule zero to one metre 0.1cm height of a table digital calipers zero to 15 centimetres 0.001cm diameter of a test tube digital micrometer screw gauge zero to 2.5 centimetres 0.0001cm diameter of a wire 🧠 parallax error ● when we use a metre rule, our eyes should be positioned such that our line of sight is perpendicular to the rule ● worn ends may introduce errors to the reading so it is better to measure from another point and subtract it from the final reading ● taking several readings and calculating the average also minimises errors

KINEMATICS term definition displacement the distance measured in a straight line from the origin speed rate of change of distance formula : speed = distance ÷ time taken unit : m/s velocity rate of change of displacement formula : velocity = displacement ÷ time taken unit : m/s acceleration rate of change of velocity formula : acceleration = change in velocity ÷ time taken unit : m/s 2 📈 displacement-time graph: ● gradient represents the velocity of the object 📉 velocity-time graph: ● gradient represents the acceleration of the object ● area under graph represents the displacement of the object

DYNAMICS I: MASS AND WEIGHT term definition gravitational field a region in which a mass experiences a force due to gravitational attraction gravitational field strength gravitational force per unit mass at a point (usually 10N/kg) mass weight a measure of the amount of matter in a body the gravitational force acting on an object that has mass scalar quantity vector quantity si unit: kg si unit: N independent of the gravitational field strength dependent on the gravitational field strength measured with a beam balance/electronic balance measured with a spring balance 🧠 F = ma ● F = resultant force (N) ● m = mass (kg) ● a = acceleration (m/s 2 ) 🧠 acceleration due to gravity (free-fall) = 10m/s 2

DYNAMICS II: FORCES term definition newton's 1 st law of motion every object will continue its state of rest or uniform motion in a straight line unless a resultant force acts on it inertia the reluctance of an object to change its state of rest or motion, due to its mass newton's 2 nd law of motion when a resultant force acts on an object of a constant mass, the object will accelerate in the direction of the resultant force newton's 3 rd law of motion for every action force, there is an equal and opposite reaction force. these forces act on different bodies terminal velocity when air resistance acting on an object equals its weight, the object starts to travel at a constant speed known as terminal velocity. this means that the object has zero acceleration friction: definition the contact force that opposes motion between surfaces in contact positive effects ● we can walk without slipping ● moving objects are able to slow down when needed negative effects ● cars are less efficient by up to 20% ● moving parts in engines, motors and machines suffer wear and tear ways to enhance friction ● using treads ● using parachute ● using chalk ways to reduce friction ● using wheels ● using ball bearings ● using lubricants and polished surfaces ● using air cushion 🔄 newton’s 3rd law of motion characteristics: ● forces always occur in pairs, each pair is made up of an action and a reaction force

● action and reaction forces are equal in magnitude ● action and reaction forces act in opposite directions ● action and reaction forces act on different bodies ● action and reaction forces must be of the same nature (contact/non-contact) 💨 characteristics of air resistance: ● it always opposes the motion of moving objects ● it increases with the speed of the objects ● it increases with the surface area (or size) of the objects ● it increases with the density of air

TURNING EFFECT OF FORCES term definition moment of a force the product of the force and the perpendicular distance from the pivot to the line of a