physics paper 1

• method to measure speed

  walking- 1. measure distance using tape measure, 2. time how long it sees you to walk distance using stop watch, 3. repeat experiment multiple times and find average

  sound- 1. two people at least 300m apart, measure distance with trundle wheel, person 1 will clap board, person 2 will press start with they see clapper, person 2 will stop when they hear clapper, sound travels much slower than speed, use v= x/t, distance is 300m and time is taken for person to hear clapper
• acceleration is a vector, it is the rate of change of velocity.
• falling objects are pulled down by gravity
• a feather falls slower than a hammer because it has largest air resistance
• if there was no air resistance, the feather and hammer would fall at the same time and hit floor at same time, the accelaration would be 10m/s^2
• A force is a push or pull, measured in newtons (N). Newtons 1st law- if a resultant force acts on an object, it will accelerate, acceleration is change in velocity over time so the velocity will change so the direction or speed of object will change (or both).

  
  

  if the resultant force is zero, there is no acceleration so moving at constant velocity (so same speed and same direction), or the object is at rest (no speed).
• A stationary car would have weigh acting below and the normal contact force acting above, a boat travelling at constant speed would have drag, thrust and weight acting on it, and a plane taking off at constant speed would have weight, thrust and drag acting on it
• • using light gates to measure speed set up two, one at start and one at end, measure distance between them, as soon as object passes through first it will measure the time taken to reach the second, use speed= distance/time, more accurate as it removes reaction time and human error with a stopwatch
• newtons second law- force=mass times acceleration

  circular motion- object moving in a circle with constant speed, the speed is constant but direction is always changing, so the velocity is always changing so it is accelerating

  
  

  force- for motion in a circle, there must be a force that supplies this acceleration, this is called centripetal force, and is directed towards the centre of the circle

  
  

  inertial mass- this is a measure of how difficult it is to change the velocity of an object
• newtons third law- every action force has an equal and opposite reaction force
• momentum is always conserved in a collision (where there are no external forces like friction, air resistance etc)
• human reaction time- there is a delay between the stimulus and the response
• ruler drop experiment- someone else holds a ruler just above your open hand, they drop it at a random time, record the distance from the bottom of the ruler to the point where it was caught, average human reaction is 0.25 seconds
• after seeing a hazard, before you react, during reaction time you travel X metres, thinking distance, then you react causing the car to slow down and stop over Y metres, braking distance
• thinking distance- speed, affected by reaction time, concentration, tiredness, distractions, influence of drugs/alcohol

  braking distance-speed, poor road conditions (icy, wet), bald tires, low friction, worn brake pad, mass
• the greater the speed, the greater the distance travelled during the same time
• when in a crash, there is a large deceleration over a very short time as you stop moving from a high speed, as force= mass times acceleration means a great force is exerted on the car, and the passengers
• before the crash, you have a large momentum due to high velocity, after the crash, you have no momentum as you are not moving, a greater force is felt
• the work done to stop a vehicle is equal to the KE of the vehicle, as all the kinetic energy has to be transferred into friction for it to stop
• energy changes

  object projected upwards- KE transferred into GPE and then GPE transferred into KE as it falls back down

  objected projected up a slope- KE transferrred to GPE (also heat if friction is present)

  movement hitting an object- KE transferred to sound/ KE transferred into obstacle that moves too

  objected being accelerated by a constant force- object is having work done, with it gaining KE

  vehicle slowing down- KE transferred to heat(through breaks)