Physics 2a – Motion and Forces Accuracy and precision Prior learning Know ways accuracy and precision can be improved In an experiment. Key words –Accuracy,

Physics 2a – Motion and Forces

Accuracy and precision

• Prior learning• Know ways accuracy and precision can be

improved In an experiment.• Key words

– Accuracy, precision, absolute error, uncertainty

Topic – Physics 2a – Motion Friday 3rd February

Physics 2a – Motion and ForcesStarter task: Recap standard

measurements / Scientific notation

Heinemann: Questions 1.1 1-5 page 41


• Define terms accuracy, precision, uncertainty and absolute error

• Use uncertainty of common lab equipment to calculate measurement with uncertainty

• Estinate the uncertainty of a result using an experiment

By the end of this lesson we should be able to:

Topic – Physics 2a


Task 1: notes

• Accuracy relates to an instrument’s use.

• An instrument is accurate if it truly reflects the quantity being measured e.g. if you wanted to measure the width of this page you would use a ruler with millimetre markings.

• Precision relates to how an instrument differentiates between slightly different quantities e.g. bathroom scales, kitchen scales and laboratory scales all measure mass and are accurate for the mass they measure.

Laboratory scales are more precise as they can measure to 0.01 g whereas bathroom scales can measure to 0.5 kg


Task 1: notesUncertainty:

• All measurements you make have some amount of uncertainty.

• The uncertainty of an instrument is usually one half of the finest scale e.g. a ruler which measures in millimetres has an uncertainty of 0.5 mm. An electronic timer usually to 0.005 s

• The uncertainty of an instrument measure its precision. If you measure the width of an A4 piece of paper you will get a reading of 21.1 cm. The uncertainty is 0.5 mm so the reading is 21.1 0.05 cm


Uncertainty in common laboratory equipment:

• Metre rule 0.05 cm • 50 mL measuring cylinder 0.2 mL • 50 mL measuring cylinder 0.2 mL • 10 mL measuring cylinder 0.1 mL• -100C – 1100C thermometer 0.50C (does depend on

precision of thermometer)


Task 2: Activity• Use a timer, ruler, thermometer and measuring

cylinder to take some measurements including the

uncertainty in each measurement.

What to measure Measurement Uncertainty Measurement with Uncertainty

Volume of water in a 50 mL measuring cylinder

Temperature of the water in the measuring cylinder

Length of the measuring cylinder

Time to walk across the classroom


Estimating the uncertainty in a result

• An experiment or a measurement exercise is not complete until the uncertainties have been analysed. The report should include an estimate of the total uncertainty. This gives the reader of the report some idea of your confidence in the result.

• The following processes are used for estimating uncertainty.1. When adding or subtracting data, add the absolute

uncertainties.1. e.g. T (change in temperature) = 40 0.5 0C - 35 0.5 0C = 5

1 0C

• When multiplying or dividing data, add the percentage uncertainties.


Absolute and % uncertainty

Physics 2a – Motion and Forces• You would calculate as follows:• Specific heat of metal to a whole number so answer so

far is cmetal = 198 J kg-1 K-1

• Uncertainty (%) = 0.120 + 0.6 + 23 + 0.476 + 1.351 = 25.547%

• Hence, you would obtain the following result: cmetal = 198 Jkg-1J-1 25.547%

now 25.547% of 198 = 50.6so cmetal = 198 51 Jkg-1J-1

• Once you have done all of this you can consider the

relative success of your measurement exercise.

• Your result is: 147 J kg–1 K–1 cmetal 249 J kg–1 K–

1


• If I then give you the actual specific heat of the metal and it falls within your values, you can conclude that your experiment is consistent with known values (accurate). Or in other words, there are probably no major errors.


Summary task

• Read pg 43/44

• Work through example 1.2A

• Then questions from text pg.45

• Check answers in the back of book

• Ask for help!!


• Define terms accuracy, precision, uncertainty and absolute error

• Use uncertainty of common lab equipment to calculate measurement with uncertainty

• Estimate the uncertainty of a result using an experiment

By the end of this lesson we should be able to:

Topic – Physics 2a

Documents

Physics 2a – Motion and Forces Accuracy and precision Prior learning Know ways accuracy and precision can be improved In an experiment. Key words –Accuracy,