physics

• Systematic errors


  The reading is larger or smaller than (or varying from) the true reading by a constant amount
• Random errors


  Scatter in readings about the true reading
• Precision


  The size of the smallest division (on the measuring instrument) or 0.01 mm for the micrometer
• Accuracy


  How close (diameter) value is to the true (diameter) value
• Instruments used to measure


  • Length: metre rule/tape
  • Diameter: micrometer (screw gauge) / digital caliper
  • Resistance: ammeter and voltmeter/ohmmeter/multimeter on 'ohm' setting
• Experimental measurements that are more accurate will have the peak/average value move towards the true value
• Experimental measurements that are more precise will have lines that are closer together/sharper peak
• Systematic errors


  e.g. constant error (in all readings), cannot be eliminated by averaging, error in measuring instrument
• Random errors


  e.g. readings scattered (equally) about true value, error due to observer, can be eliminated by averaging
• Ways to reduce systematic error in micrometer readings


  • Check for zero error (on micrometer)/zero the micrometer
• Acceleration


  Change in velocity/time (taken) or rate of change of velocity
• Speed


  Distance/time and has no direction
• Velocity


  Displacement/time and has magnitude and direction
• Distance


  Sum of lengths moved
• Displacement


  Straight line between two points and is a vector
• Scalar quantity


  Has magnitude only
• Vector quantity


  Has magnitude and direction
• Mass


  Property of a body resisting changes in motion/quantity of matter in a body/measure of inertia to changes in motion
• Weight


  Force due to the gravitational field/force due to gravity
• Situations where mass is constant but weight changes


  • Change in gravitational field strength
  • Change in fluid surrounding body
• Newton's second law


  (Resultant) force proportional/equal to rate of change of momentum
• Conservation of momentum


  Total momentum of a system (of colliding particles) remains constant provided there is no resultant external force acting on the system/ isolated or closed system
• Newton's first law


  A body/mass/object continues (at rest or) at constant / uniform velocity unless acted on by a resultant force
• Momentum


  Mass x velocity
• Kinetic energy


  Momentum^2 / 2 x mass
• Pressure


  Force/area (normal to force)
• Deriving pressure due to liquid


  1. Use of m=pV and use of V=Ah and use of F=mg

  2. Correct substitution to obtain p=pgh
• Explaining pressure exerted by gases

  1. Molecules/atoms/particles in (constant) random/haphazard motion

  2. Molecules have a change in momentum when they collide with the walls

  3. Force exerted on molecules therefore force on the walls

  4. Reference to average force from many molecules/many collisions
• Pressure at top of mountain

  • Fewer molecules per unit volume
  • Temperature is less
  • Hence lower speed of molecules
  • Hence less pressure
• Deriving pressure exerted by liquid on base

  1. Pressure=Force/Area

  2. Weight (of liquid)/Force (on base) = Ahpg

  3. Pressure=hpg
• Frequency of a progressive wave

  • Number of oscillations per unit time of the source/of a point on the wave/of a particle (in the medium)
  • Number of wavelengths/wavefronts per unit time passing a (fixed) point
• Loudspeaker moving towards observer causes rise in/higher frequency, loudspeaker moving away from observer causes fall in/lower frequency
• Diffraction of a wave

  • Wave incident on/passes by or through an aperture/edge
  • Wave spreads (into geometrical shadow)
• Longitudinal wave


  Vibrations/oscillations (of the particles/wave) are parallel to the direction or in the same direction (of the propagation of energy)
• Transverse wave


  Vibrations/oscillations (of the particles/wave) are perpendicular to the direction (of the propagation of energy)
• Doppler effect


  Change/difference in the observed/apparent frequency when the source is moving (relative to the observer)
• When a distant star is moving away from a stationary observer, the wavelength increases/frequency decreases/red shift
• Adjustments to produce stationary waves on a stretched string

  • Alter distance from vibrator to pulley
  • Alter frequency of generator
  • Change tension in string by changing value of the masses
• Diffraction


  Spreading/diverging of waves/light (takes place) at (each) slit/element/gap/aperture
• Interference


  Overlapping of waves (from coherent sources at each element)