Mechanics

• Scaler quantity


  A quantity that only has magnitude e.g. Density energy time etc
• Moment

  The turning effect of a force

  the force (N) x the perpendicular distance (m) between the pivot and line of action of the force

  can be clockwise or anticlockwise

  measured in Nm
• Equilibrium


  No net (resultant) forces or moments act on it

  forces and moments are balanced
• Conditions required for equilibrium


  The resultant force acting on the body must be zero

  the principle of moments must apply about any point on the body
• Principle of moments states 


  Sum of clockwise moments about any point in an object = sum of anticlockwise moments about the same point
• A Couple


  A pair of forces acting in a body that are of equal magnitude and opposite direction, acting parallel to one another, but not along the same line

  forces acting this way produce a turning force or moment
• Uncertainty


  The interval that a value is said to lie within with a given level of confidence
• Absolute uncertainty


  Expressed in the units of the quantity measured.

  either half the range of a set of results, half the resolution of a single reading ( some readings require two judgments)
• Percentage uncertainty


  Absolute uncertainty expressed as a percentage of the mean value

  %u=(AU/mean value)x100
• Random error


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


  Causes all readings to differ from the 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
• Accuracy


  A measure of how close a measurement is to the true 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
• Repeatable 


  The same experiment can repeat measurement using the same method and equipment and obtain the same value
• Reproducible


  An experiment can be repeated by 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
• Anomalous results


  A result that doesn’t fit with the pattern of other results in a set of data
• Categoric data 


  Data that CAN be sorted into categories or groups
• Continuous data


  Data that can have any value or scale
• Reading

  A piece of experimental data requiring only one judgment E.g. thermometer, top-pan balance, measuring cylinder, digital voltmeter, Geiger counter, pressure gauge
• Measurements 


  A piece of experimental data requiring two judgments E.g ruler, vernier calipers, micrometer, protractor, stopwatch, any analouge meter
• Valid result


  A result which answers the question it was intended to answer
• Reliable result


  A result that can be consistently reproduced in independent experiments
• Vector quantity


  A quantity that has both a magnitude and an associated direction e.g. force friction momentum etc
• displacement


  A distance in given direction
• speed


  The change of distance travelled per unit time.

  The rate of change of displacement
• velocity


  The change of displacement per unit time.

  the rate of change of displacement
• What is acceleration 


  The change of velocity per unit time

  The rate of change of velocity
• What is acceleration of free fall

  Acceleration of an object acted on only by the gravitational force
• What is a projectile


  An object which has been projected
• What is projectile motion

  A projected object in motion acted on only by the gravitational force.
• what is the gradient of a distance-time graph

  Gives the instantaneous speed of an object
• What is the gradient of a velocity-time graph

  Gives the instantaneous acceleration of an object
• What is the area under a velocity-time graph

  Gives the displacement of the object