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Chapter 3 (average velocity (average velocity = change in displacement /…

- - - - steeper gradient = higher speed
- - - - upwards = increasing displacement
      - downwards - decreasing displacement
    - - on a curved displacement-time graph find the gradient of a tangent to find the instantaneous velocity.
- - - - The vertical velocity changes due to acceleration of free fall
      - the vertical displacement and time of flight can be calculated using equations of motion
      - horizontal velocity remains constant
        
        the component of acceleration in the horizontal direction is zero.
        
        horizontal acceleration = gcos90° =0
  - - - as the horizontal velocity is a straight line, we can calculate it using pythag
  - - - horizontal component of the velocity is vcosθ, and the initial vertical upwards component of the velocity is vsinθ
- - - - for curved v-t graph, use gradient of a tangent for instantaneous acceleration
- - - - the acceleration of free fall is g (9.81ms^-2 on earth)
        
        Values for g varies all around the earth e.g. 9.825 in Helsinki, 9.816 in london etc
  - - - some methods are
        
        Electromagnet and trapdoor
        
        An electromagnet hlds a small steel ball above a trapdoor. When the current is switched off, a timer is triggered, the electromagnet demagnetises and the ball falls.
        When it hits the trapdoor, the electrical contacgt is broken and the timer stops. The value for g is calculater from the height of the fall and the time taken.
        
        Light gates
        
        The electromagnet and trapdoor introdudce tiny delays into the timing. Instead we can use light gates, two light beams, one above the other with detectors connected to a timer.
        When the ball falls through the first beam, it interrupts the light and starts the timer. When the ball falls through the second beam a known distance further down, the timer stops.
        
        Taking pictures
        
        A small metal ball is dropped from rest next to a metre rule, and its fall is recorded on video or with a camera in rapid-fire reoeating mode. (alternatively a stroboscope illuminates the scene with rapid flashed)
        The camera shutter is held open, producing a photograph with multiple images of the falling ball. The position of the ball at regular intervals is then determined by examing the recording
    - - using s = ut + 0.5at²
        
        becomes s = ut + 0.5gt²
        
        Plotting a graph of s on the y axis, and t² on the x-axis will get a graph of gradient(m) of g/2
- - - - thinking distance
        
        the distance travelled between the moment you first see a reason to stop, to the moment when you use the brake
        
        these are affected by factors such as
        
        speed of vehicle
        
        condition of brakes
        
        tires / condition of tires
        
        road
        
        thinking distance = speed x reaction time
        
        the greater the speed or reaction time the greater the vehicle will travel before the driver applies the breaks
      - braking distance
        
        the distance travelled from the time the brake is applied until the vehicle stops