Paper 2

• Forces- Scalar and Vector Quantities

  -Scalars only havemagnitude(size) e.g.speed-Vectors have magnitude anddirectione.g.velocity-Arrows are used to represent vectors where the length of the arrow shows magnitude and the way it faces is the direction-The diagram such as shown in the image is afree body diagram-Forces are vectors

  
• Forces- Contact and Non-contact forces

  -Aforceis a push or a pull acting on an object due to interaction with another object. Force is avector-Contactforces requires the objects to touch such as tension, friction and air resistance-Non-contactforces apply when the objects aren't touching such as gravity, electrostatic force and magnetism
• Forces- Gravity

  -Gravity is a force ofattractionbetween all masses-Gravity on Earth is due to itsgravitational field-Massis related to the amount of matter in an object-Weightis the force acting on an object due to gravity and the objects mass-Gravity on Earth is 9.8N/kg-This also means weight and mass aredirectly proportional-Centre of massis the single point where the weight of an object may be considered to act through-The equation for weight is shown in image

  
• Forces- Resultant Forces

  -When multiple forces act on one object, it can be seen as asingle forcethat has the same affect as all the forces added up-This is called the resultant force

  
• Forces- Vector Diagrams for same direction or diagonal forces

  -Vector diagrams require ascaleof cm to newtons-When the forces act in the same direction you simplyadd the lengthsto draw one big resultant force-For diagonal forces they can be split into two forces: thehorizontalandvertical-These forces add up to make the same size as the original diagonal force-The separation into two lengths helps determine the overall effect on the object

  
• Forces- Vector Diagrams for two angled forces

  -Forces can act on each other atangles, vector diagrams allow us to calculate the resultant force1) A scale should be decided e.g. 1cm=1N2) Draw a point to represent the object3) Draw a line to represent one of the forces (10N) and use a protractor to draw the other force (8N) at the angle given (30°)4) Draw the other force to the head of the top force at the same angle and then join the lines together to make a parallelogram5) Draw a line for the object to the other tail of the parallelogram, this is the resultant force

  
• Forces- Energy stores

  -Thermal energy

  -Kinetic

  -Gravitational potential energy

  -Elastic potential energy

  -Magnetic

  -Chemical (chemical bonds, what humans use for energy)

  -Electrostatic

  -Nuclear (from breaking an atom)
• Forces- Work Done

  -When a force causes an object tomove, energy is transferred-This is calledwork-Energy is transferred because it requires energy to move the object (mustovercomethe resistive forces like friction)-The movement of an object is calleddisplacement-For example, when a man is moving a box, the work done to overcome thefrictioncauses an increase inthermalenergy. This means the energy in the mans chemical energy store has been converted to the thermal energy store of the box.-The distance must be in thesame line of actionas the force

  -One joule of work is done when one newton causes a displacement of one metre-One joule = 1 newton metre of workmeaning one joule of energy causes a displacement of one metre-The equation for work done is shown in the image

  
• Forces- Energy Transfer

  -Energy can be transferred between stores in many waysThese include:-Mechanicallysuch as physically stretching a rubber band-Electricallysuch as plugging something into a socket-Heating-Radiationsuch aslightandsoundwaves
• Forces- Work done applied to brakes in a car

  -The car has a kinetic energy storing as it is a moving object-When brakes are applied, the brake presses against the wheel-This means a force of friction acts between the brake an wheel-Work done by the frictional forcecauses thekinetic energy storeto transfer to thethermal energystore of the brakes

  
• Forces- Work done when applied to a person going up stairs

  -The person is moving upwards so they are movingagainsttheforce of gravity-The force of gravity acting on them is theirweight-Therefore theforcehere is their weight and the distance is thedistanceof the person off the ground-So work done is weight x distance off ground-Remember only the distance in thesame line of actionof the force is relevant-This means only the vertical distance is relevant as weight acts downwards-Here the personschemical energystore has been transferred to theirgravitational potential energystore

  
• Forces- Elastic and inelastic deformation


  -Multiple forcesare required tochange the shapeof an object such as pulling on both ends of a spring otherwise the forces would beimbalancedand the object would move

  -When stretching, stretching forces areequal in magnitudebutopposite in direction.(forces are balanced)-When squeezing, squeezing forces areequal in magnitudebutsame in direction.-Three forces are needed to bend an elastic material as shown in image-Elastic materials will return to their original length/ shape if the forces on them are removed. This iselastic deformation.-If it doesn't return to its original shape it isinelastic deformation-Certain polymers are inelastic

  
• Forces- Extension

  -Theextensionof a spring is directly proportional to the force applied such as weight (linearon a force-extension graph)-However once thelimit of proportionalityis reached doubling force wont double extension (force- extension graph becomesnon-linear)-Limit of proportionality is point where elastic material starts to be inelastically deformed (wont return to old shape)-Force (N)= spring constant (N/M) x extension (m)applies whilst it is directly proportional-Extension can also becompression-The spring constant is the same value until limit of proportionality-This find the force needed to stretch an elastic object-When we stretch or compress an object, we are using aforceto dowork-Thework doneto stretch or compress a spring isequalto theelastic potential energystored in the spring if it has not beeninelastically deformed(before limit of proportionality)

  
• Forces- Required practical: Relationship between force and extension

  1) Set up equipment as shown

  2) Measure the spring length

  3) Add 100g to the mass holder

  4) Measure the extension of the spring

  5) Repeat steps 3-4 for a range of masses from 100g-1000g at 100g intervals

  IV: Mass on spring DV: Extension CV: Spring

  Errors: The spring may become inelastically deformed meaning further measurements are incorrect

  
• Forces- Movements, Levers and Gears

  -A moment is the turning effect when a force causes an object to rotate about apivot-Equation of a moment is shown in image, Moment =Nm-When an object isbalanced, the total clockwise and anti-clockwise moments are equal-Leversandgearscan be used totransmitrotational effects of forces andmagnifythesizeof the force or thedistancethe force moves-When a gear moves a gear double the size, the force is doubled. However the smaller gear rotates twice every one rotation of the larger gear meaning work done is the same.-For calculations with gears you measure theradius

  
• Forces- Pressure in a Fluid

  -A fluid can either be gas or liquid-Particles in fluids collide with their containers, creating a forcenormalto the surface-The equation for pressure is shown in image, pressure is measured in pascals (pa), area is metres squared-When pressure acts on a bigger area, abigger forceis created. This is used in hydraulics

  
• Forces- Atmospheric Pressure

  -The atmosphere is a relatively thin layer of gas around Earth-The greater the altitude, the less dense the atmosphere and the lowering theatmospheric pressure-At a higher altitude there is less air above a surface so there is smaller amount of molecules and therefore weight of air acting on the surface (force) , lowering the pressure
• Forces- Pressure in a Column of Liquid

  -Pressure at a particular part in a column of liquid depends on liquiddensityand theheightof the column above the pointThe higher the column-The greater theweightabove the point-The greater theforceon the surface at that point-The greater thepressureThe more dense the liquid:-Theweightof the fluid increases due to more particles-This means there would be more force from the fluid above the same point, increasingpressure

  -The equation for pressure is shown in the image,height= metres, density= kg/metres cubed

  
• Forces- Upthrust

  -When an object issubmergedthe bottom surface experiences a greater pressure than the top due to the height of column-This creates an upwards resultant force called Upthrust-The size of an Upthrust isequalto the weight of the liquid displaced.-An objectfloatswhen its weight is equal to the Upthrust andsinkswhen it is greaterAn object less dense than the liquid:-Displacesa volume of liquid greater than its own weight so it will rise-Will float with some of the object remaining below the surface-Will displace liquid ofequalweight to the object

  -An object with low density will have more of the object above the surface-An object denser than liquid cant displace enough liquid to equal its own weight so sinks

  
• Forces- Distance and Displacement

  -Distance is ascalarquantity so doesn't account where it ends up-Displacement is avectorquantity as it has a direction so tells you how far an object has moved from its origin (overall journey)
• Forces- Speed

  -Speed is ascalarquantity (m/s)-Speed is often an average-The speed of sound is 330m/s-The speed of a walking human is 1.5m/s-The speed of a running human is 3m/s-The speed of a cycling human is 6m/s-The equation for speed is shown in the image

  
• Forces- Velocity

  -Velocity is avectorquantity-When travelling in a straight line, an object with a constant speed has a constant velocity (no direction change)-When an object turns, velocity changes though speed can still be constantAn object travelling in a circle:-is constantly changing velocity (direction)-accelerating, even if travelling a constant speed (velocity is increasing due to changing direction)
• Forces- Newton's First Law

  -Newtons first lawstates that an object will remain in the same velocity unless acted on by a resultant force-If there isno resultant forces,stationary objects stay stationary and moving objects continue to move at aconstant velocity(speed and direction)-This means if there is a change in velocity there must be a resultant force-Inertiais the tendency for objects to continue in the same state of motion
• Forces- Distance-time graphs

  -A distance-time graph can be used to represent the motion of an object travelling in a straight line-The speed of an object is found from thegradient-A straight horizontal line shows a stationary vehicle-If an objectaccelerates, it draws an upwards curve-We use atangentsgradient to find its speed at a particular time

  
• Forces- Acceleration

  -The equation for acceleration is shown in image, Change in velocity= m/s, time= seconds-The acceleration of an object in free fall is 9.8m/s^2-When an object slows down, the change in velocity is negative and so is acceleration-Another equation is used to calculateuniform acceleration(constant rate)V^2 - U^2 = 2as, you will be given this equationV= final velocity, U=initial velocity, a= acceleration, s= distance

  
• Forces- Velocity-Time Graphs

  -Thegradientof a velocity-time graph finds the acceleration of an object-The area under the graph is the total distance travelled

  
• Forces- Newton's Second Law

  Learn this well!!!:-The acceleration of an object isdirectly proportionalto the resultant force acting on the objects andinversely proportionalto the mass of the object

  -If resultant force doubles, acceleration doubles-If mass doubles, acceleration halves-The equation can be seen in image

  
• Forces- Inertial mass

  -Mass is a measure ofInertia-Inertial massis a measure of how difficult it is to change a given object's velocity-The inertial mass is defined as theratioof the force needed to accelerate an object over the acceleration produced-The larger the inertial mass, the larger theforceto producea given accelerationthan an object with a smaller inertial mass
• Forces- Average road speed facts


  -Cars travel at13m/son amain roadand30m/son amotorway-To accelerate from a main road to a motorway it requires an acceleration of2m/s^2-For a typical family car this requires2000N
• Forces- Terminal Velocity

  When an object falls through a fluid (gas or liquid):-At first, the object accelerates due to gravity-As it speeds up, resistive forces increase-The resultant force reaches zero when the resistive forces balance the gravitational forces. This is terminal velocity.

  -The acceleration due to Earth's gravity is 9.8m/s^2-A speed-time graph is shown in image

  
• Forces- Newton's Third Law

  -Newton's third law states when twoobjectsinteract, the forces they exert on each other are opposite and equal-This means if an object exerts a force on an object. The other object exerts the force back-This is why space ship thrusters cause it to rise

  
• Forces- Momentum

  -The equation for momentum and change in momentum is shown in image,momentum=kg m/s-When an unbalanced force acts on amovable/ movingobject there is a change in momentum-To calculate change in momentum you sub the equation for acceleration into the equation for resultant force-This means forceequals/is the rate of change of momentum,-This the reason forsafety devicessuch as crumple zones in cars or seatbelts. They increase the time of a fixed change in momentum and therefore reduce the force felt on impact.

  
• Forces- Conservation of Momentum

  -In a closed system, the total momentum before an eventequalsthe total momentum after the event-This means you can find the new velocity or new mass using the momentum equation

  
• Forces- Stopping Distance

  Stopping Distance depends on:-Thethinkingdistance (distance for the driver to react)-Thebrakingdistance (distance travelled under braking)

  -The greater the speed the greater the braking force-Thinking distance isdirectly proportionalto speed-Doubling the speed increases the braking distance by a factor of four

  
• Forces- Reaction time


  -Reaction times vary from0.2-0.9seconds-This can result in quite some distance before breaking-Reaction time is affected by tiredness, sobriety and distractions
• Forces- Factors Affecting Braking Distance

  -The braking distance can be affected by the conditions of theroad, vehicleandweather-Vehicles can have worn brakes or tires or incorrect tire inflation-To stop a car the brakes apply a force to the wheels, the greater the force the greater the deceleration-Work is doneby thisfrictional forceto transfer kinetic energy to thermal, heating the brakes-The equation for work done is shown in image-To find the size of the braking force required, the work done equation can be used where distance is braking distance

  
• Forces- Problems with heavy braking

  -If the braking force istoo large, brakes can overheat and tyres can lose grip. This is more likely in worn tyres or brakes.-Basically the brakes will overheat and the car will lose control
• Waves- Transverse and longitudinal waves


  -Waves transferenergy, not particles-The particles of a waveoscillatearound a fixed point-In transverse waves the oscillations areperpendicularto the direction of energy transfer-In longitudinal waves the oscillations areparallelto the direction of energy transfer
• Waves- Properties of waves

  -Frequencyis the number of waves passing a point per second, measured in Hz, one Hz means one wave per second-Amplitudeis the maximum displacement of any particle from its undisturbed position-Amplitude indicates the amount of energy a wave carries-Wavelengthis the distance from one point to another similar point such as distance between two wave peaks-Periodis the time taken for one complete oscillation in secondsPeriod (T) = 1 ÷ Frequency (Hz)

  
• Waves- Wave speed

  -The speed of a wave is how quickly energy is transferred (speed of waves movement)-It is a measure of how far the wave moves in one second-It is found using the equation shown-Speed is m/s. Wavelength is metres. Frequency is Hz-As waves are transmitted from one medium to another their speed and thereforewavelengthchanges-Thefrequencyremainsthe same as the same number of waves are being produced by the source per second-Due to the wave equation, speed and wavelength aredirectly proportional