Key Point about Q # 2 Identifying limitations [2007 June 31] (i) Relevant points must be underlined and ticked. Some of these might be: A Two sets of readings not enough (to draw valid conclusion) B Hard to judge rebound height, with reason C Parallax (error in measuring h) D Difficult to release without applying a force E Rule may not be vertical / perpendicular F Only cm divisions on rule (if borne out by readings) G Inconsistent bounce Suggesting improvements (ii) Relevant points must be underlined and ticked. Some of these might be: A Take several d values and plot graph/compare e values B Use video and play back slowly/position sensor C Method of reducing parallax problem (adjustable marker/drop many times to refine value of h/assistant to drop ball/ensure measurement taken at eye level) D Mechanical method of release/hold ball against stop E Method of making rule vertical G Use flat surface/turn off fans [] Page 1 of 38
Transcript
Key Point about Q # 2Identifying limitations [2007 June 31](i) Relevant points must be underlined and ticked. Some of these might be:
A Two sets of readings not enough (to draw valid conclusion)B Hard to judge rebound height, with reasonC Parallax (error in measuring h)D Difficult to release without applying a forceE Rule may not be vertical / perpendicularF Only cm divisions on rule (if borne out by readings)G Inconsistent bounce
Suggesting improvements(ii) Relevant points must be underlined and ticked. Some of these might be:
A Take several d values and plot graph/compare e valuesB Use video and play back slowly/position sensorC Method of reducing parallax problem (adjustable marker/drop many times to refinevalue of h/assistant to drop ball/ensure measurement taken at eye level)D Mechanical method of release/hold ball against stopE Method of making rule verticalG Use flat surface/turn off fans
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Identifying limitations(i) Underline and tick relevant point (one from each section):
A - two sets of readings are not enough (to draw a conclusion)B - difficult to make accurate cylinder shape - cylinder radius/circumference variesC - cylinder doesn’t roll straightD - human reaction error (in timing) - measured time is very short not ‘difficult to release cylinder and start stopwatch together’E - difficult to judge end point
Suggesting improvements(ii) Underline and tick relevant point (one from each section):
A - test many cylinders and plot a graph- test many cylinders and find many values of kB - method of making more accurate cylinderD - time over longer distance - use shallower angle ramp - use light gates/pressure switches to measure time - use freeze-frame photography to measure time - use motion sensor to measure time not just ‘use video’ not ‘repeated readings’ not just ‘use computer/data logger’E - mark distance with lines on ramp (to eliminate parallax) not ‘use a pointer’X - new method (e.g. vernier calipers) to measure average diameter
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Identifying limitations(i) Relevant points must be underlined and ticked.Some of these might be:
A Only two readings (are not enough to draw a valid conclusion).B Hard to judge/see (when/where) highest position with reference to movement. Do not accept reaction time ideas.C Parallax (error) or good diagram demonstrating this.D Difficulty in release/keeping rule still prior to release (reference to force).E Equilibrium position changes with evidence shown in measurements.X Other additional source of error.
Suggesting improvements(ii) Relevant points must be underlined and ticked.4Some of these might be:
A Take more readings and plot a graph/calculate k values.B High speed (camera to take) photographs/film the motion and play back frame by frame/ slow motion/ use pause OR motion/position sensor above/ below mass OR trial and error with light gate/ horizontal marker.C Measure at eye level/repeat to get eye in right place/ place rule as close as possible to vertical rule/use helper to release or measure/use mounted pin at end of rule (to help locate position on scale).
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D Use a named method to release the rule e.g. cotton and candle or scissors/electromagnet/end stop or clamp.X cm rule – use a mm rule. Need to see evidence in their previous measurements that their readings are taken to the nearest cm or 0.5 cm.Y Other additional solution, well explained.
Do not allow ‘repeated readings, vacuum, draft free room’Do not allow ‘use a computer to improve the experiment’Do not allow ‘increase range/change load on ruler/change length of ruler/changing quality of ruler’
Identifying limitations(i) Relevant points must be underlined and ticked. Some of these might be:
A Two sets of readings not enough (to draw valid conclusion).B Cone may have not reached terminal velocity.C Hard to see when cone strikes floor.D Cone falls at an angle (due to draughts/imbalance of cone).E Human error in timing/reaction time.F Difficult to measure diameter because cone flexible.G Parallax error (at reading positions).X Other source of error
Suggesting improvements(ii) Relevant points must be underlined and ticked.Some of these might be:
A Take more readings and plot a graph/calculate ratios.B Ensure terminal velocity by increasing release height/measure velocity at two intervals to check terminal velocity reached.C Use pressure/other sensor (on floor) to stop timer/use assistant to judge when it reaches the floor.D Turn off fans/balance the cone e.g. extra strip of tape.E1 Use light gate to trigger stopwatch/use video camera with slow motion replay/use multiflash photography/use high speed camera with known time intervals.E2 Time over greater distance.F Measure diameter of cone in two directions and average.G Drop in front of rule/read at eye level.Y Another improvement, well explained.Do not allow ‘repeated readings’ (unless qualified by ‘plot a graph’).
Do not allow ‘use a computer to improve the experiment’
