Experimental Error vs Human Mistakes
Identifying uncertainty, mistakes, and ways to improve investigations
Experimental Error vs Human Mistakes
Identifying uncertainty, mistakes, and ways to improve investigations
Science - Grade 6-8
- 1
A student measures the same pencil three times with a ruler and gets 14.8 cm, 14.9 cm, and 14.8 cm. Is this more likely experimental error or a human mistake? Explain.
Look for small, reasonable differences between repeated measurements.
This is most likely experimental error because small differences can happen when reading a ruler. The measurements are close together, so there is no sign of a large mistake. - 2
During a lab, a student forgets to zero the digital scale before measuring a beaker of water. The mass is recorded as 128 g, but the empty beaker's mass was included by accident. Is this experimental error or a human mistake? Explain.
Think about whether the problem came from normal limits of measuring or from not following the procedure.
This is a human mistake because the student forgot a required step. Zeroing the scale or subtracting the beaker's mass would have prevented the wrong measurement. - 3
A thermometer can only be read to the nearest 1 degree Celsius. Two students reading the same water sample record 22 °C and 23 °C. Is this more likely experimental error or a human mistake? Explain.
This is most likely experimental error because the thermometer has limited precision. A small difference of 1 degree can happen when people estimate a reading between marks. - 4
A group is testing how sunlight affects plant growth. They accidentally water one plant twice as much as the others. Is this experimental error or a human mistake? Explain how it could affect the results.
Identify the variable that was supposed to stay controlled.
This is a human mistake because the group did not keep the water amount the same for all plants. It could affect the results because extra water might change plant growth, making it harder to tell the effect of sunlight. - 5
Define experimental error in your own words. Include one example from a science lab.
Experimental error is the natural uncertainty or variation that happens when measurements are made, even when the procedure is followed correctly. For example, a ruler measurement may vary by a millimeter because a person has to estimate between marks. - 6
Define human mistake in your own words. Include one example from a science lab.
A human mistake is an avoidable error caused by doing something incorrectly or not following the procedure. For example, recording 35 mL instead of 53 mL is a human mistake. - 7
A student writes the temperature as 71 °C in a data table, but the thermometer actually showed 17 °C. Is this experimental error or a human mistake? Explain.
Check whether the error came from measuring or from recording the data.
This is a human mistake because the student copied or wrote the number incorrectly. The problem was not caused by the measuring tool's normal uncertainty. - 8
A class measures the time it takes a toy car to roll down a ramp. Trial times are 2.31 s, 2.28 s, 2.34 s, and 2.30 s. What does the small spread in the data suggest?
The small spread suggests normal experimental error from timing and measurement limits. The results are consistent because all trials are close to each other. - 9
A different group measures the same toy car ramp and records 2.3 s, 2.4 s, 9.8 s, and 2.3 s. Which value is most likely caused by a human mistake, and why?
Look for the data point that does not fit the pattern of the other trials.
The value 9.8 s is most likely caused by a human mistake because it is very different from the other trials. The student may have started or stopped the stopwatch at the wrong time. - 10
A balance scale always reads 2 g too high because it is not calibrated correctly. Is this random error, systematic error, or a human mistake? Explain.
Systematic error affects measurements in a consistent way.
This is systematic error because the scale is consistently off in the same direction. It is not random because the error is predictable, and it may not be a human mistake if the user did not know the scale was miscalibrated. - 11
A student reads the bottom of the meniscus in a graduated cylinder and records 42 mL. Another student reads from above the cylinder and records 44 mL. What type of issue is shown, and how can it be reduced?
This shows experimental error caused by viewing the measurement from different angles. It can be reduced by reading the bottom of the meniscus at eye level each time. - 12
Explain why repeating trials helps reduce the effect of experimental error.
Think about why one measurement might not represent the whole experiment well.
Repeating trials helps because random small errors may be different each time. Scientists can average the results to get a value that is more reliable than a single measurement. - 13
A student spills part of a chemical sample but continues the experiment and records the result without telling the group. What is the main problem with this data?
The main problem is that the data may be invalid because a human mistake changed the amount of sample. The student should report the spill and repeat the trial if possible. - 14
For each situation, label it as experimental error or human mistake: A. A stopwatch reaction time causes a 0.1 s difference. B. A student uses the wrong chemical. C. A ruler has marks only every 1 mm. D. A student skips trial 3 but writes down a made-up value.
Experimental error can happen even when the procedure is followed. Human mistakes are usually avoidable.
A is experimental error because reaction time creates small measurement uncertainty. B is a human mistake because the wrong chemical was used. C is experimental error because the ruler's precision is limited. D is a human mistake because the student invented data instead of doing the trial. - 15
A lab report says, 'Our results were wrong because of human error.' Rewrite this statement to be more scientific and specific.
Avoid vague phrases. Name the action, tool, or measurement that caused the problem.
A better statement would identify the exact problem, such as, 'One trial may be inaccurate because the timer was started after the car had already begun moving.' Scientific explanations should describe the specific source of error or mistake.