howscienceworks taking measurements

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Teachers Notes

This sequence of slides is designed to introduce, and explain thetaking of measurements, including the meaning ofvariation, range,

mean (average) and the difference between accuracy & precision,as explained on page 362 in New Physics for You, 2006 & 2011editions.

Note : When you start this PowerPoint if you see a message about Read-only embedded fonts thenyou are recommended to select Open Read-Only as this (i) gives a clearer font for those at theback of the room and (ii) ensures that the text-highlighting of key words is correct.

On each slide the key points are revealed step by step, at the click ofyour mouse (or the press of a key such as the space-bar).

Before making the next mouse-click you can ask questions of the classor make statements about what is about to be revealed.

This should help students to become clearer about the ideas involved.

Naturally it pays to have quick practice-run first.

To start the slide-show, press function-key F5(or right-click->Full Screen)(to return to normal view press the key).

For more (free) PowerPoint presentations, visitwww.physics4u.co.uk


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How Science works:

New Physics for You, page 362

TakingTaking

measurementsmeasurements


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About taking measurements,

The meaning of variation, range andmean (average),

The meaning of accuracy and

precision.

Learning Objectives

You should learn :


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Taking measurements

When you take measurementsthere may be some variationin the readings.

If you time the fall of a paper parachuteover a fixed distance, the times may varyslightly.10.1 s, 10.2 s, 9.9 s, 10.0 s, 10.3 sLets look at these results more closely.

For example:


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Taking measurements

The results were:

10.1 s, 10.2 s, 9.9 s, 10.0 s,10.3 s

What is the Range of theseresults?


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Taking measurements : Range

The results were:

10.1 s, 10.2 s, 9.9 s, 10.0 s, 10.3s

and the maximumvalue

Range = from min tomax

= 9.9 to10.3

Find the minimumvalue


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Taking measurements : Mean

The results were:

10.1 s, 10.2 s, 9.9 s, 10.0 s, 10.3sWhat is the mean (or average)

of these results?


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The results were:

10.1 s, 10.2 s, 9.9 s, 10.0 s, 10.3sAdd up the 5 numbers:

10.1+10.2+9.9+10.0+10.3 = 50.5

There are 5 items, so divide by 5:

Mean (or average) == 50.5

5

= 10.1s


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The results were:

10.1 s, 10.2 s, 9.9 s, 10.0 s, 10.3sWhy is it a good idea to calculate

the mean of your results?

Because it improves the reliabilityof your results.

Your results will be more reliable.


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Accuracy

Precision

and


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Definitions Accuracy andPrecision soundthe same thing

is there a

difference??


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Definitions : Accuracy

In your experiments, you need toconsider the accuracy of your measuringinstrument.For example:

An expensive thermometer

is likely to be more accuratethan a cheap one.

It will give a result nearerto the true value.

It is also likely to be more sensitive(with a better resolution). It willrespond to smaller changes in

temperature.


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As well as accuracy,precision is also important.

For example:

Precision is connected to

the smallest scale divisionon the measuring instrumentthat you are using.

Definitions : Precision


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For example, using a ruler:


A ruler with a millimetre

scalewill give greater precisionthana ruler with a centimetre

scale.


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For example:

A precise instrument alsogives a consistent readingwhen it is used repeatedlyfor the same measurements.



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For example, 2 balances:

A

B

A beaker is weighed on A, 3times:

The readings are: 73 g, 77 g,71 g

It is then weighed on B, 3 times:The readings are: 75 g, 73 g,74 g

So the Range is= 73 g 75 g = 2g

Balance B has better precision.

Its readings are grouped closertogether.


So the Range is= 71 g 77 g = 6g


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Accuracy compared withPrecision

Suppose you are measuring thelengthof a wooden bar:0

The length has a true value

truevalue

Lets look at 3 cases

And we can take

measurements of the length,like this:


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Accuracy compared withPrecision

0

truevalue

0

0

Precise(grouped)but notaccurate.

Accurate(the mean)but notprecise.

AccurateandPrecise.


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The meaning of variation and range,

How to calculate the mean (or

average),

and why this improves the reliability ofyour results,

The difference between accuracy andprecision.

Learning Outcomes

You should now understand:


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For more details, see:

New Physics for You, page 362

For more free PowerPoints, visit

the web-site at

www.physics4u.co.uk


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If you are connected to the web atthe moment, click below to seewhats available:

http://www.physics4u.co.uk/
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