In the fields of science precision and accuracy mean two very different things. Accuracy is defined to be how close the result value is to the actual value. Precision is basically being able to reproduce the same result in other trials. In the hypothetical data given to us from Alf, Beth, Carl, and Dee, Dee is the most accurate and Carl is the most precise. Alf’s data is very clumsy and the fact that his average is so close to the actual value for gravity is luck. His individual data was up to 2.18 above the actual value. Since the other trials were below the actual speed, this abnormally high value compensated for the other low values to give a value close to the actual speed. Beth is in between the others for her precision and accuracy. Her accuracy is not bad and her average is also fairly close. Carl is by far the most precise of the group. His deviation from the average was never more than 0.04. Usually if the precision is high, and the accuracy is low, there was an error involved in the experiment or calculations. The handout points out that since Carl’s speed was below the actual speed, friction might have caused his speed to be too low. Dee had the over-all best lab. Her accuracy is very close and her precision is fairly good too.
There are three types of error involved with experiments, personal, systematic, and random. Because we are only human we are all vulnerable to personal error. This is the experimenter messing up. This could be done by reading a temperature wrong, measuring the wrong amount of something, or miscalculating the data. These errors are different from the other two types because they can all be eliminated by being careful. Systematic errors are usually errors in the equipment that are consistent, so the experiment sill has good precision. This is caused from a flaw in the equipment, like a scale may read 6 grams, when the actual mass is 5 grams. It is always good to be skeptical of the equipment and check it before using it. Another type of systematic error is failure to account for all of the variables acting on the equipment. The third type of error is random error. These are errors that are unpredictable, and caused by unknown variables in the experimental process. Common types of random error include temperature change, mechanical vibrations, and other physical variations. In principle, all systematic and human error can be eliminated, but random error can never be eliminated. In order to keep your experiments accurate and precise, one must always be very careful when conducting experiments, and always keep a close eye on the equipment.