A community for students.
Here's the question you clicked on:
 0 viewing
Dipankar
 3 years ago
HELP!!
i have a question!! Infact 2 questions about measurement uncertainty
In 149.9 ± 0.1 cm .... does 0.1 cm actually means 0.0999999999999 and we round it off to 0.1 . i think what i am saying is right but still want to confirm from some expert
next question 
in case of 4 units  3 units where least count is 1 units
answer will be 1 ± 2 units ? this method doesn't make sense in this case.
Dipankar
 3 years ago
HELP!! i have a question!! Infact 2 questions about measurement uncertainty In 149.9 ± 0.1 cm .... does 0.1 cm actually means 0.0999999999999 and we round it off to 0.1 . i think what i am saying is right but still want to confirm from some expert next question  in case of 4 units  3 units where least count is 1 units answer will be 1 ± 2 units ? this method doesn't make sense in this case.

This Question is Open

Carl_Pham
 3 years ago
Best ResponseYou've already chosen the best response.0You're misinterpreting the notation. The notation "149.9 +/ 0.1 cm" is not, despite appearances, the addition of two measurements. It's just a shorthand way of saying "the answer lies with some high probability between 149.8 cm and 150.0 cm." So you should not assign a measurement uncertainty to both the "149.9" and the "0.1", which it sounds like you are trying to do. The correct place at which to round the +/ bit is determined by your error analysis for the 149.9 bit, whatever it was. It is traditional to give only one digit in the +/ bit, although I suppose you could argue for different notations, depending on how the error analysis was done. In the second case, you are applying the rules of assigning measurement uncertainty mindlessly, using the sig dig rules, which you should not do. Always begin assigning measurement uncertainty by thinking about the measurement process and how error might accumulate. In the case of counting objects up to a number of 4, there are very few measurements I can imagine where it would be appropriate to assign any measurement uncertainty at all. Most such measurement will have an appropriate measurement uncertainty of zero. That is, they are what are often called "exact numbers." They have "infinite" significant digits, you might say. There are certainly cases where things you count should be assigned some measurement uncertainty. For example, if you dump a big box of marbles on the floor and try to count them by eye. If you spend 5 minutes on it and get 24,335, you might well assign a measurement uncertainty of +/ 10 marbles. But if you did it very carefully, over 2 hours, you might again assign an uncertainty of zero. Assigning measurement uncertainty is a judgment call, although there are mathematical tools that can usefully model some error processes. But mostly you use common sense.
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.