Go Back   Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

Like Tree2Likes
  • 2 Post By ChipB
Reply
 
LinkBack Thread Tools Display Modes
Old Oct 29th 2016, 02:22 AM   #1
Junior Member
 
Join Date: Oct 2016
Posts: 5
I need someone hel pto clarify my problem

Question:
A student used a digital stopwatch three time 10 oscillations of a pendulum. The timings were 13.52s, 13.64s and 13.58s
a) Calculate i the average time for 10 oscillations, ii the time period of the oscillations.
b) Estimate the accuracy of the timings, giving a reason for your estimate.


The problem i have is with part b. In maths to estimate is round up ideally to 2 sf.(my answer is 1.4 to s.f)
if i give my estimate my answer how do i give a reason. I feel to give my estimate to 2 sf because it seems to be the standard in physics (i could be wrong)
but also knowing that gate timers and other forms of measuring time make be more effective than a stopwatch am i suppose to estimate the time on those and give it as my answer since it will be more accurate?

I just a bit confused and need a second opinion
alisdfd is offline   Reply With Quote
Old Oct 29th 2016, 06:58 AM   #2
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,347
You are estimating the accuracy of the timing using the stop watch. it doesn't matter that there may be more accurate ways to measure it - the data you were given is from the stop watch.

As for an estimate of accuracy - the max deviation of any one measurement from the mean is 0.06s. So +/- 0.06s is one estimate of accuracy. However, given that there are only 3 data points it's quite possible that if a 4th measurement was taken it could very well lie outside the +/- 0.06s "window" about the mean value. So you could argue that the accuracy is a little worse than +/- 0.06s; perhaps +/- 0.1s.
topsquark and alisdfd like this.
ChipB is offline   Reply With Quote
Old Oct 29th 2016, 09:40 AM   #3
Senior Member
 
Join Date: Aug 2010
Posts: 434
Originally Posted by alisdfd View Post
Question:
A student used a digital stopwatch three time 10 oscillations of a pendulum. The timings were 13.52s, 13.64s and 13.58s
a) Calculate i the average time for 10 oscillations, ii the time period of the oscillations.
b) Estimate the accuracy of the timings, giving a reason for your estimate.


The problem i have is with part b. In maths to estimate is round up ideally to 2 sf.(my answer is 1.4 to s.f)
Who told you this? In physics or engineering (there is no reason to "round" in maths) the rule is that a measurement is accurate to 1/2 the most significant figure. If we are measuring a length with a meter stick, for example, we look at the end of the object being measured. If it lies between two marks, we take the one it is closest to so that our accuracy is 1/2 the distance between marks. That is, "13.52 s" could be anywhere from 13.515 to 13.525. Those figures are given to four significant figures and the accuracy is 0.005 s.

if i give my estimate my answer how do i give a reason. I feel to give my estimate to 2 sf because it seems to be the standard in physics (i could be wrong)
but also knowing that gate timers and other forms of measuring time make be more effective than a stopwatch am i suppose to estimate the time on those and give it as my answer since it will be more accurate?

I just a bit confused and need a second opinion
The accuracy of a measurement depends upon the instrument used to measure so it makes no sense to base the accuracy on "more accurate" instruments you did not use!

Last edited by HallsofIvy; Oct 29th 2016 at 09:43 AM.
HallsofIvy is offline   Reply With Quote
Old Oct 30th 2016, 10:24 AM   #4
Junior Member
 
Join Date: Oct 2016
Posts: 5
Originally Posted by ChipB View Post
You are estimating the accuracy of the timing using the stop watch. it doesn't matter that there may be more accurate ways to measure it - the data you were given is from the stop watch.

As for an estimate of accuracy - the max deviation of any one measurement from the mean is 0.06s. So +/- 0.06s is one estimate of accuracy. However, given that there are only 3 data points it's quite possible that if a 4th measurement was taken it could very well lie outside the +/- 0.06s "window" about the mean value. So you could argue that the accuracy is a little worse than +/- 0.06s; perhaps +/- 0.1s.
thank u
alisdfd is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Tags
clarify, hel, pendulum, problem, pto, time



Thread Tools
Display Modes



Facebook Twitter Google+ RSS Feed