Forces and Energy Transfer

� Speed=distance/time� Average Speed = average of 2 different speeds� Velocity = speed in a particular direction oftravel.� Acceleration = increase in speed from stationaryor a speed to its desired speed.� Acceleration is rate of change of speed� A = Change in speed/time taken: Therefore� A = v-u/t� V = final velocity� U = beginning velocity� Or: V^2 = U^2 + 2AS� OR: S = ut+ � at^2� UNITS: M/S/S, M/S^2, MS^-2Average Speed Equation:V+U/2 = S[(][distance)]/T* Equations of Motion:* Average Speed = V+U/2 = S/T* Acceleration = V-U/T* V2 = U2 + 2AS , S = UT+1/2AT2* V = final velocity U = Initial Velocity A = Acceleration T = TimeS = distance* Scalar quantities, = magnitude only* Eg, Mass, Speed, Time* Vector quantities = magnitude and direction* EG, Weight, Acceleration, displacement* In a distance time graph, gradient = speed* In a speed time graph, the area under the graph is the distance* Acceleration on a velocity time graph is the gradientForces* Measured in Newtons* Show 2 things:direction and magnitude* Resultant of 2+ forces = single force that is equivalent to thecombination.* Forces make objects: accelerate, decelerate and change directionNewtons 2nd Law of Motion* Objects resist a change in velocity* UNBALANCED FORCES CAUSE ACCELERATION* Size of acceleration is different for different objects* Amount of accel depends also on MASS IE:* Force (n) = mass(kg) + acceleration (m/s/s)* N2lProjectiles* Find Vertical and Horizontal component of vel* Vertically use EQNS of motion* 3. Horiz usE S = d/tW=MGNewtons 3rd Law of motion* For every action there is an equal and opposite reaction* For instance when you kcik a football, the football kicks you backas such* Why is it a bad idea to drive into a concrete post at 70 KPH?* According to Newtons 3^rd law the block will apply the same forceon the car as the car applies on the block.

Except the block isprobably buried in cement, so it would remain still but the carwould continue, or try to continue, to go forward unless brakingforces were applied, so the car would go straight into the blockand the car would crumple.Car Safety* P=Mv* Momentum = Mass x Velocity* Units: Kgms^-1* Mass is the same anywhere in the universe but weight is not.* W=mg when g = gravitational field strength* Overall stopping distance of a car depends on thinking distanceand braking distance.Stretching Materials* Most materials will change shape when a small force is applied tothem but will return to their original shape when then force isreleased.* Materials which do this = elastic* Not = plastic* If we apply a load to a spring tiw ill extend, more we apply moreit will extend* When we remove, the load the spring retirns to its original length* But if we apply to much, the spring will be damaged and willl notreturn, it is passed it’s ELASTIC LIMIT.* Robert Jooke, fount extension is proportional to load provided elnot exceeded = Hooke’s LawEnergy* Can’t be created, just reused* Changes from 1 type to another e.g.

Kinetic to Heat* Principle of Conservation of energy �Energy exists in differentforms and can transfer between them. Everything need energy* Different forms* Fuels store chemical energy* People and machines can convert this energy into other forms toallow them to do useful tasks.* Energy us never lost or destroyed* Always converted* Forms of energy:* Kinetic* Heat* Chemical* Electrical* Light* Sound* Gravitational Potential Energy* Energy: Different Forms* Conserved* Required to do useful thingsPotential Energy is affected by gravity, mass and height* Potential energy is given to objects if they fall* Objects have more potential energy if they are higher* Objects have more kinetic energy if they move faster or have moremass.* IE: PE = MGHKinetic Energy* To do with movement* The faster u go, the more Kinetic Energy* Mass and Velocity affect kinetic energy.* KE = � MV^2Energy and WorkEnergy:Differnet Forms:KE = � MV^2P.E = mghConservationDoing Useful things WORK.Work:Work Done = Energy transferredMechanical Work done = Force x distancePOWERRate at which work is doneWork Done/Time Taken = energy transfer/time takenUnit = Watt = 1J/SMomentumProduct of mass and velocityVECTOR quantityWhen 2 object act on each other, total momentum remains constantPressureWhen forces act effect spread over an area.Product is the force acting on an area: P=F/AIncrease pressure, decrease are / increase forceHydraulicsVolume of liquid can’t be reduced by squeezing it.

Liquids pass on anypressure that is appliedLiquids transmit pressure equally in all directions liquids can beused as FORCE MULTIPLIERSProperties are used in hydraulic machinesVolume of gas can be reduced by squeezing because they can pass onsome of the pressurem but not all of it because they can be compressedE.g: If the input force is 10N and the input area is 0.1 m2 in ahydraulic jack, and the output area is 0.

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5 m2, then what is themaximum load that can be lifted?First: what is the pressure on the oil = input force/input area =10/0.1 = 100 N/M^2This pressure is transmitted thought the liquid:Output force = Pressure x Output Area100 x 0.5 = 50Ngas particles move about freely at high speed, in a solid particlesvicrate and cannot change positions.

A solid has a fixed shape and volume. Particles = vibrate but cannotmoveNo attractions between particles in a gas.Brownian motion = looking down a microscope into a chamber with smokeparticles. Can see particles moving in a haphazard fashion which isbecause the air molecules are pushing it. Byt this I mean that theaprticles are being bombarded by air molecules and therefore itchanges direction.

Boyles LawFor a fixed mass of gas at constant temperature, the pressure isinversely proportional to the volume.If the volume is halved, the pressure doublesPresuure x volume always has the same valueP1 x V1 = P2 x V2The gas laws:Speed of molecules in a gas reduews as the temperature fallsPressure is directly proportional to the Kelvin temperature (for afixed mass of gas at constant volume. Similar relationship betweenvolume and temperature: The volume is directly proportional to thetemperaturePV/t = constMomentTurning effect of a force dpends on the size of the forace and theperpendicular distance from the point of application to the pivot.Moment = Force x distanceSum of clockwise moments = sum of anti-clockwise moments.Electricity* Resistors get hot when electric current passes through them* Voltmeters placed in parallel ammeters in series* V = IR* Current is a flow of charge* It Transfers energy to the different components within the circuit* We control current by adding or removing obstructions* Resistance = V/I* Ohm’s law states that current through a wire is directlyproportional to the voltage across it unless temperature is notconstant* Bulb doe not obey Ohms Law its VI graph is not a straight linebecause as current increases the temperature changes* P = VxI* I = Q/t* V = E/Q* R = V/I* P = VI* P = E/T* I = a* Q = c* T = s* V = v* P = w* E = J* R = Ohms* Thermistor reduces resistance as temperature increasesElectrical Power is the rate of energy transfer in WattsP = E/tOr P = Current x P.DAlso IxVE = VxIxTProve that P = VxIP = E/TP = Vq/(Q/I)So P = VI

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