Units, measurements and uncertainty - …...2015/10/02 · Units, measurements and uncertainty...

Units, measurements and uncertainty

Fundamental science: Physics

•  Process of comparing measured values against reference or fundamental values

•  Expressed in numbers and units

•  Some quantities are in simplest form, others are chosen for convenience

Fundamental units

Fundamental and derived SI units

Topic 1: Measurement and uncertainties 1.1 – Measurements in physics

PRACTICE: SOLUTION: •The correct answer is (D).

FYI •The body that has designed the IB course is called the IBO, short for International Baccalaureate Organization, headquartered in Geneva, Switzerland and Wales, England. •The IBO expects you to memorize the fundamental units.

FYI: “Funky print” practice problems are drawn from old IB tests

FYI: Blue headings are assessment criteria put out by the IBO

Derived units

•  Involves measurement of two or more fundamental quantities

•  For example: acceleration: m 𝑠↑−2  momentum: Ns

SI unit – system international units

•  How to find a fundamental unit? •  Think about a formula. For example find

the fundamental unit of Force and energy •  Force = Newton N and E = Joule J

Force = mg = kg m𝑠↑−2 

PE = mgh = kg m 𝑠↑−2 m = kg 𝑚↑2 𝑠↑−2 

Derived Units expressed in SI units

𝑘𝑔 𝑠↑−2 𝐴↑−1  𝑘𝑔 𝑚↑2  𝑠↑−2 𝐴↑−1 

Prefix – in data booklet

Standard form and scientific notation Standard form: 1200 000 Scientific form: 1.2 x 10↑6  Changing big numbers: positive exponent, move right

•  Standard form: 0.0000012 •  Scientific form: 1.2 x 10↑−6 

Using a micrometer screw gauge

Range: 0 – 25mm Accuracy ~ 0.01mm = 0.0001m

How to read a micrometer

Check for zero error

Fig 1 What is the micrometer reading here?

Fig 1 What is the micrometer reading here? 7.

Fig 1 What is the micrometer reading here? 7. 38 mm

Fig 2 What is the micrometer reading here?

Fig 2 What is the micrometer reading here? 7

Fig 2 What is the micrometer reading here? 7 . 72 mm

Fig 3 What is the reading here? …….mm

Using Vernier calipers

How to read a Vernier caliper Metric Vernier Caliper Reading - YouTube [720p].wmv

Fig 1 What is the reading that should be recorded here? Answer: ......... mm

Fig 1 What is the reading that should be recorded here? Answer: 37...... mm

Fig 1 What is the reading that should be recorded here? Answer: 37.46...... mm

Fig 2 What is the reading that should be recorded here? Answer: 34 ......... mm

Fig 2 What is the reading that should be recorded here? Answer: 34.60......mm

Fig 3 What is the reading that should be recorded here? Answer: .40........ mm

Fig 3 What is the reading that should be recorded here? Answer: .40.00.....mm

Recording uncertainties

•  What is the length of the pencil? •  How sure are you in each case?

Example

•  How would you state the error in each case?

Example

SOLUTION: • 6.2 is the nearest reading. • The uncertainty is certainly less than 0.5.

Practice

SOLUTION: • Find the average of the two measurements: (49.8 + 50.2) / 2 = 50.0. • Find the range / 2 of the two measurements: (50.2 – 49.8) / 2 = 0.2. • The measurement is 50.0 ± 0.2 cm.

Absolute error – your choice •  Limit of reading is the smallest graduation

of the scale of an instrument •  Uncertainty is at least 1/2  of the limit of

reading •  In most cases the uncertainty is greater

than the limit of reading

For each object find the limit of reading, the uncertainty and state the measurement

Units, measurements and uncertainty - …...2015/10/02 · Units, measurements and uncertainty...

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