Uncertainty

Audi SG

Some basic doubts to clarify.

Let's say I want to find the uncertainty of this displacement which takes on this formula s=0.5at^2, do i INCLUDE the 0.5 in my uncertainty equation?

I read through the rules today and found this:

If a reading is multiplied by a constant k, the uncertainty is also multiplied by k.

z = kx the uncertainty will be uncertainty z = k (uncertainty x)

so I saw ANOTHER example, which is p = pi r^2 R/ L (where p is resistivity and L the length of wire)

when they find the uncertainty of p, pi wasnt included in the equation. So i am wondering whether i should include 0.5 when finding the uncertainty of s = 0.5at^2. I still dont get why pi isnt included in finding the uncertainty of p.

Thanks!

eagle SG

Your question is very general. Pls show an example working. You mentioned seeing examples, but I wouldn't know exactly what example you saw, what question was it, and what your workings and problems are.

Please do note that there's a difference between finding uncertainty and percentage uncertainty. I believe you were doing the latter.

wee_ws SG

Hi,

Given s = 0.5 at^2.

Then we have

(delta s) / (s_0) = (delta a) / (a_0) + 2 (delta t) / (t_0),

where s_0, a_0, and t_0 are given values of s, a, and t respectively.

Constants are not considered by the fact that no certainty arises from a value that is always fixed.

Thanks.

Cheers,
Wen Shih

Audi SG

Hi,

Given s = 0.5 at^2.

Then we have

(delta s) / (s_0) = (delta a) / (a_0) + 2 (delta t) / (t_0),

where s_0, a_0, and t_0 are given values of s, a, and t respectively.

Constants are not considered by the fact that no certainty arises from a value that is always fixed.

Thanks.

Cheers,
Wen Shih

Thanks all, I already knew how to solve this question :)

I do know constants are not considered but how about cases which abide by this rule:

For z = kx, the uncertainty will be uncertainty z = k (uncertainty x)

In this case, we do multiply the constant.

Thanks!

wee_ws SG

Hi,

Which book or notes did you refer to?

I have not come across this rule in my IB Physics text or in JJC lecture notes. Thanks.

Cheers,
Wen Shih