<< Chapter < Page Chapter >> Page >
A = πr 2 = 3 . 1415927 . . . × 1 . 2 m 2 = 4 . 5238934 m 2 size 12{A=πr rSup { size 8{2} } = left (3 "." "1415927" "." "." "." right ) times left (1 "." 2" m" right ) rSup { size 8{2} } =4 "." "5238934"" m" rSup { size 8{2} } } {}

is what you would get using a calculator that has an eight-digit output. But because the radius has only two significant figures, it limits the calculated quantity to two significant figures or

A = 4 . 5 m 2 , size 12{A" = "4 "." 5" m" rSup { size 8{2} } } {}

even though π size 12{π} {} is good to at least eight digits.

2. For addition and subtraction: The answer can contain no more decimal places than the least precise measurement . Suppose that you buy 7.56-kg of potatoes in a grocery store as measured with a scale with precision 0.01 kg. Then you drop off 6.052-kg of potatoes at your laboratory as measured by a scale with precision 0.001 kg. Finally, you go home and add 13.7 kg of potatoes as measured by a bathroom scale with precision 0.1 kg. How many kilograms of potatoes do you now have, and how many significant figures are appropriate in the answer? The mass is found by simple addition and subtraction:

+ 1 7.56 0 kg = 15.2 kg . - 1 6.052 kg = 15.2 kg . + 13.7 00 kg + 15.208 kg = 15.2 kg . alignl { stack { size 12{7 "." "56"`"kg"} {} #size 12{ - 6 "." "052"`"kg"} {} # size 12{ { {+"13" "." 7`"kg"} over {"15" "." "208"`"kg"} } ="15" "." 2`"kg" "." } {}} } {}

Next, we identify the least precise measurement: 13.7 kg. This measurement is expressed to the 0.1 decimal place, so our final answer must also be expressed to the 0.1 decimal place. Thus, the answer is rounded to the tenths place, giving us 15.2 kg.

Significant figures in this text

In this text, most numbers are assumed to have three significant figures. Furthermore, consistent numbers of significant figures are used in all worked examples. You will note that an answer given to three digits is based on input good to at least three digits, for example. If the input has fewer significant figures, the answer will also have fewer significant figures. Care is also taken that the number of significant figures is reasonable for the situation posed. In some topics, particularly in optics, more accurate numbers are needed and more than three significant figures will be used. Finally, if a number is exact , such as the two in the formula for the circumference of a circle, c = r size 12{c=2πr} {} , it does not affect the number of significant figures in a calculation.

Perform the following calculations and express your answer using the correct number of significant digits.

(a) A woman has two bags weighing 13.5 pounds and one bag with a weight of 10.2 pounds. What is the total weight of the bags?

(b) The force F size 12{F} {} on an object is equal to its mass m size 12{m} {} multiplied by its acceleration a size 12{a} {} . If a wagon with mass 55 kg accelerates at a rate of 0 . 0255  m/s 2 size 12{0 "." "0255"" m/s" rSup { size 8{2} } } {} , what is the force on the wagon? (The unit of force is called the newton, and it is expressed with the symbol N.)

(a) 37.2 pounds; Because the number of bags is an exact value, it is not considered in the significant figures.

(b) 1.4 N; Because the value 55 kg has only two significant figures, the final value must also contain two significant figures.

Got questions? Get instant answers now!

Phet explorations: estimation

Explore size estimation in one, two, and three dimensions! Multiple levels of difficulty allow for progressive skill improvement.



  • Accuracy of a measured value refers to how close a measurement is to the correct value. The uncertainty in a measurement is an estimate of the amount by which the measurement result may differ from this value.
  • Precision of measured values refers to how close the agreement is between repeated measurements.
  • The precision of a measuring tool is related to the size of its measurement increments. The smaller the measurement increment, the more precise the tool.
  • Significant figures express the precision of a measuring tool.
  • When multiplying or dividing measured values, the final answer can contain only as many significant figures as the least precise value.
  • When adding or subtracting measured values, the final answer cannot contain more decimal places than the least precise value.

Questions & Answers

lExplain what happens to the energy carried by light that it is dimmed by passing it through two crossed polarizing filters.
Christoper Reply
What is specific heat capacity?
hamidat Reply
Specific heat capacity is the amount of heat required to raise the temperature of one (Kg) of a substance through one Kelvin
formula for measuring Joules
Rowshan Reply
I don't understand, do you mean the S.I unit of work and energy?
what are the effects of electric current
What limits the Magnification of an optical instrument?
Naeem Reply
Lithography is 2 micron
what is expression for energy possessed by water ripple
Prabesh Reply
what is hydrolic press
Mark Reply
An hydraulic press is a type of machine that is operated by different pressure of water on pistons.
what is dimensional unite of mah
Patrock Reply
i want jamb related question on this asap🙏
sharon Reply
What is Boyles law
Pascal Reply
it can simple defined as constant temperature
Boyles law states that the volume of a fixed amount of a gas is inversely proportional to the pressure acting on in provided that the temperature is constant.that is V=k(1/p) or V=k/p
what is motion
Mua Reply
getting notifications for a dictionary word, smh
what is escape velocity
Shuaibu Reply
the minimum thrust that an object must have in oder yo escape the gravitational pull
what is a dimer
what is a atom
how to calculate tension
Deena Reply
what are the laws of motion
what is force
Ugwu Reply
Force is any quantity or a change that produces motion on an object body.
A force is a push or a pull that has the tendency of changing a body's uniform state of rest or uniform state of motion in a straight line.
plsoo give me the gravitational motion formulas
What is the meaning of emf
Chinedu Reply
electro magnetic force
Electromotive force (emf) is a measurement of the energy that causes current to flow through a circuit.
Practice Key Terms 6

Get the best College physics course in your pocket!

Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?