Using light gates is a great way to get students familiar with data loggers. Systematic error: A measurement error where results differ from the true value by a consistent amount each time. Random error: a measurement error due to results varying in an unpredictable way. The gradient will be unchanged, and the systematic error should be easily detected.Īnother approach, incidentally, would be to plot \(2s\) against \(t^2\), giving a simpler gradient of \(g\). For example, if the height is measured 1 cm too short each time, the line on the graph will be shifted downwards. Systematic errors can often be eliminated by plotting a graph. Might lead on to a discussion about systematic errors (should the graph pass through the origin?).Allows \(g\) to be determined from a gradient, an important skill.Shows that \(g\) is (more-or-less!) constant: the graph is a straight line.Helps to spot anomalies visually – an indication of random error.In the film, Christina and Alom drop the ball from different heights and collect a lot of (not very good!) data quickly. If you’re going to plot a graph, however, you might as well have two meaningful variables. Much better would be to exclude anomalous values first, and better still would be to plot a graph of \(h\) against \(t^2\) to spot those anomalies. Your students could just repeatedly drop the g-ball from the same height and average all their data, then substitute their average \(t\) into \(s = \fracgt^2\) to find \(g\). How is this better than using a stopwatch?.In the film, Alom and Christina use an L-shaped bracket clipped to a metre rule to press the release switch, to aid a clean release. The switch release can limit accuracy, but overall the g-ball is a quick way to collect a large number of data points. Like most stopclocks, it measures to a resolution of 0.01 seconds. The g-ball starts timing when released and stops timing as soon as it hits the floor. There appear to be at least two manufacturers, Unilab and Mollic). We’ve found other UK suppliers: Philip Harris, Better Equipped, Breckland Scientific. These cost about £20 + VAT from education suppliers, one of which is Timstar (as of Timstar appear to have stopped selling the G Ball. Uncertainty: the interval within which the true value can be expected to lie. This is us showing our age! A better term might be ‘resolution’.Īccuracy: a result is accurate if it is close to the true value. In the film, at about 2:22, the word ‘precision’ is used to mean the timer’s smallest scale division. ![]() The ASE book The Language of Measurement (£13.50/£8.50 members) refers to precision as:Ī measurement is precise if values cluster closely. There’s more error handling in some of the other films in the series, and we’re planning to complete a film specifically about error as the series continues. ![]() Since we anticipate this practical being used early in the A level course, we’ve not included comments about how to do a full error analysis. It’s good to compare at least two methods (even if one is shown as a demonstration only), to prompt and inform discussion about precision, accuracy and uncertainty. Which of these methods you use might depend on your students’ skill, your own preference, apparatus availability, ease of data collection or processing, and class size. Use an electromagnetic switch to release a ball bearing, with triggered timing.Drop a ‘g-ball’, which times its own fall.Drop a ball and time its fall with a stopwatch.Where Ð"y represents distance traveled between breaks and Ð"t represents the time of travel between breaks.The film shows four different methods of measuring g using a falling object: We used the Science Workshop program to calculate the velocities and accelerations due to gravity of the picket fence between breaks in the beam using Recorded Data, Calculated Results, and Graphs The Datastudio software recorded for the amounts of time between breaks. ![]() The photogate sent to the computer a signal when its beam was broken by one of the dark bands. We dropped the picket fence through the photogate, which was connected to the computer through the Science Workshop 700 interface. ![]() *ĝell computer with Science Workshop 700 interface
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