OCR Physics

• Absolute Uncertainties:

  • The interval that a value is said to lie within, with a given level of confidence
• Accuracy:

  • A measure of how close a measurement is to the true value
• Analogue Apparatus:

  • Measuring apparatus such as rulers, beakers and thermometers that rely on the experimenter reading off a scale to determine the measurement
• Anomalies:

  • Data points that don’t fit the pattern of the data
  • Repeat readings help remove anomalies
• Control Variables:

  • Variables that must remain the same throughout an experiment so as to not affect the results
• Dependent Variables:

  • The variable being measured in an experiment
  • It is dependent on the independent variable
  • The dependent variable should be plotted on the y-axis of a graph
• Digital Apparatus:

  • Measuring apparatus such as ammeters, voltmeters and digital calipers that digitally measure and display a measurement
• Fiducial Marker:

  • A thin marker, such as a splint, that is used to ensure readings are taken from the same place each time
  • They are used to improve the accuracy of measurements
• Gradient:

  • The change in the y-axis value over the change in the x-axis value between two points
  • If the graph is curved, a tangent can be drawn to calculate the gradient at a specific point
• Independent Variables:

  • The variable that is changed by the experimenter in an experiment
  • The independent variable should be plotted on the x-axis of a graph
• Line of Best Fit:

  • A line drawn on a graph to demonstrate the pattern in the plotted data points
• Percentage Uncertainties:

  • The uncertainty of a measurement, expressed as a percentage of the recorded value
• Precision:

  • A measure of how close a measurement is to the mean value
  • It only gives an indication of the magnitude of random errors, not how close data is to the true value
• Prefixes:

  • Added to the front of units to represent a power of ten change
• Random Errors:

  • Unpredictable variation between measurements that leads to a spread of values about the true value
  • Random error can be reduced by taking repeat measurements
• Repeatable:

  • The same experimenter can repeat a measurement using the same method and equipment and obtain the same value
• Reproducible:

  • An experiment can be repeated by a different experimenter using a different method and different apparatus, and still obtain the same results
• Resolution:

  • The smallest change in a quantity that causes a visible change in the reading that a measuring instrument records
• Resolution of Forces:

  • The splitting of a force into its horizontal and vertical components
• Scalar Quantities:

  • A quantity that only has a magnitude, without an associated direction
  • Examples include speed, distance and temperature
• SI Units:

  • The standard units used in equations
  • They are: metres, kilograms, seconds, amps, Kelvin and moles
• Significant Figures:

  • A measure of a measurement’s resolution
  • All numbers except zero are counted as a significant figure
  • When zeros are found immediately after a decimal place, they too are counted
• Systematic Errors:

  • Causes all readings to differ from the true value by a fixed amount
  • Systematic error cannot be corrected by repeat readings, instead a different technique or apparatus should be used
• Triangle of Forces:

  • A method of finding the resultant force of two forces
  • The two forces are joined tip to tail and the result is then the vector that completes the triangle
• Vector Quantities:

  • A quantity that has both a magnitude and an associated direction
  • Examples include velocity, displacement and acceleration
• Vernier Scales:

  • The type of scale used on calipers and micrometers, that involve reading from a fixed scale and a moving scale to produce accurate measurements
• Zero Errors:

  • A form of systematic error, caused when a measuring instrument doesn’t read zero at a value of zero
  • This results in all measurements being offset by a fixed amount
• Acceleration is the rate of change of velocity
• Average speed is the distance over time for the entire region of interest
• Braking distance is the distance travelled between the brakes being applied and the vehicle coming to a stop
• Displacement is the direct distance between an object's starting and ending positions, a vector quantity with both direction and magnitude
• Displacement-Time Graphs show how displacement changes over time, with the gradient giving the velocity and curved lines representing acceleration
• Free-Fall occurs when the only force acting on an object is gravity
• Instantaneous speed is the exact speed of an object at a specific given point
• Projectile Motion is the motion of an object fired from a point and only affected by gravity, often split into horizontal and vertical components for problem-solving
• Reaction Time is the time taken to process a stimulus and trigger a response, affected by alcohol, drugs, and tiredness
• Stopping Distance is the sum of thinking distance and braking distance for a driven vehicle
• Thinking Distance is the distance travelled during the driver's reaction time, affected by alcohol, drugs, and tiredness
• Velocity-Time Graphs show how velocity changes over time, with the gradient giving acceleration and curved lines representing changing acceleration
• Velocity is the rate of change of displacement, a vector quantity with both direction and magnitude