AP Physics 1 - We Can Do This!

​In AP Physics, you'll need to be able to record mathematical calculations to

the correct number of significant digits.  While many teachers simply use the

rule of 3 significant digits, you can be penalized for using too few or too

many digits, especially in experimental work.  

 

Significant does not mean important when referring to values, it means

"measured to."    When you write a number like 200 mL with no decimal

place, you are saying that you were measuring liquids like this:  100 mL,

200 mL, 300 mL.  Each value could be off by as much as 50 mL which is

huge and would cause lots of error in an experiment.  These values all have

1 significant digit and sloppy measurements.

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On the other hand, if you used a quality graduated cylinder, you could write a value of 200.0 mL because it was exact.  You are now saying that the value is 200.0 mL which is +/-.05 mL which is a precise value.  It  has 4 significant digits.

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You should have gotten pretty good at significant digits (I will call them sig digs in class) in pre-AP chemistry.  But here are the rules:

1) all non-zero values are significant.  1234 g = 4 significant digits

2) all zeros that are sandwiched between non-zeros are significant.  104 N = 3 significant digits, 104.05 = 5 significant digits.

3) All zeros AFTER a decimal and ALSO after a non-zero are significant.  .0052 = 2 significant digits, but 52.00 = 4 significant digits.

 

In most calculations, 3 significant figures are acceptable in AP Physics. For the record, this "rule" drives your teacher up the wall because there are rules for significant digits and they are either significant or they are not and there are rules for this, but welcome to College Board, darling.

 

In experimental work, use the number of digits in your data.  For example, a measurement of 12.345 g from a digital balance gives you five significant digits and you'll need to take all of them into account.  A force probe might read 1.008 N and you would want all 4 significant digits.

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As a rule of thumb, use the correct number of significant digits based on the equipment used in an experiment - even if it is 5 or 6 digits and then follow the rules for calculations on problems.

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http://tinyurl.com/jgj5f6r. This is a Kahn Academy based assignment.  Look to the left on the site and you'll see five links to complete. The video is only 5 min long.  When you are done, go to:

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http://www.sciencegeek.net/APchemistry/APtaters/sigfigs.htm.  This is a 20 question online quiz not just on counting significant digits, but also on measuring and making calculations with them.  You may take it as many times as necessary to make a perfect score.  Take a screen shot of it on your computer or phone, take a photo of it, or print it out and bring it to our first class meeting.  Do not text any photos of work this summer.  I do not yet have a grade book, so there is no place for them to go.

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When you are done, go back to the main page.