physics P2A

physics P2A

1. graphs

   • distance-time graphs
     • shows the distance something has travelled and in how much time
     • features
       • gradient = speed
       • flat sections = stationary
       • straight = steady speed
       • the steeper the graph, the faster the object is travelling
       • downhill = going back toward starting point
       • curves = acceleration or deceleration
       • steepening curve = speeding up
     • calculating speed
       • speed = gradient
   • velocity-time graphs
     • velocity - the speed of the object with direction specified (30mph north or 20m/s 060)
     • features
       • gradient = acceleration
       • flat sections = steady speed
       • steeper = greater acceleration or deceleration
       • uphill = acceleration
       • downhill = deceleration
       • curve = changing acceleration

2. forces

   • weight, mass and gravity
     • weight
       • caused by the pull of the gravitational field
       • mass X gravitational field strength
       • Newtons
     • mass
       • just the amount of 'stuff' in an object
       • kg
     • gravity
       • the force on an object implemented by the strength it is being held to the planet with
   • resultant forces
     • the overall force on a point or object
     • change in velocity
     • if the resultant force on a stationary object is zero,the object will remain stationary
     • if there is no resultant force on a moving object it'll carry on moving at the same velocity
     • if there is a non-zero resultant force, then the object will accelerate in the direction of the force
   • when two objects interact, the forces they exert on each other are equal and opposite
   • friction
     • always slows things down
     • air resistance increases as speed increases
     • objects falling through fluids reach terminal velocity
       • fluids = air or liquid
       • terminal velocity = maximum speed
       • terminal velocity depends on shape and area
         • larger area = slower velocity
         • larger shape = slower velocity
   • a force is any external effort that causes an object to undergo a certain change, either concerning its movement or direction
   • forces change momentum
     • when a force acts on an object, it causes a change in momentum
       • larger force means a faster change of momentum
       • if someone has a quick change of momentum, the forces on the body will be very large

3. energy

   • stopping distances
     • sum of thinking distance and braking distance
       • thinking distance
         • affected by two things
           • how fast you are travelling
             • faster you are going, the further you will go
           • how dopey you are
             • tiredness
             • drugs
             • alcohol
             • careless
       • braking distance
         • affected by four things
           • how fast you are going
             • faster you are travelling, further it takes to stop
           • how good the brakes are
             • better brakes, shorter distance
           • how good the tyres are
           • how good the grip is
             • road surface
             • weather
             • tyres
   • work and potential energy
     • when a force moves an object through a distance, the energy transferred and work is done
     • work done = force X distance
     • gravitational potential energy = mass X gravitational field strength X height
   • Joules (J)
   • kinetic energy = 1/2 X mass X speed^2
   • kinetic energy transferred = work done by brakes
   • kinetic energy gained = potential energy lost
   • work done = power X time
   • momentum = mass X velocity

4. car design

   • brakes
     • the brakes reduce the kinetic energy
       • transferring it into heat and sound energy
     • regenerative braking systems
       • 1) use the system that drives the vehicle to do the majority of the braking
       • 2) rather than converting the kinetic energy into heat energy, the brakes put the vehicle in reverse. with the motor running backwards, the wheels slow
       • 3) the motor acts as a electric generator, converting kinetic energy into electrical that is strored in the vehicle's battery.
       • 4) this means that energy from braking is not wasted
   • safety
     • crumple zones
       • at front and back of the car crumple up on impact
       • the car's kinetic energy is converted into other forms of energy by the car body as it changes shape
         • e.g. heat energy
     • side impact bars
       • strong metal tubes fitted into car door panels.
       • help direct kinetic energy of the crash away from passengers to other areas of the car
         • e.g. the crumple zones
     • seat belts
       • stretch slightly, increasing the time taken for the wearer to stop
       • reduces the forces acting on the chest
         • some of the kinetic energy of the wearer is absorbed by the seat belt stretching
     • air bags
       • slow you down more gradually
       • stop you from hitting the hard surfaces
   • power ratings
     • the size and design of car engines determine how powerful they are
     • the more powerful the engine it transfers from its fuel every second, and so the faster its op speed can be
     • aerodynamic
       • less air resistance
       • air flows very easily and smoothly past the car
       • can travels at higher speeds