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Uncertainties Problem Solving class 1 for Physics 1A and Higher Physics 1A Uncertainties Problem Solving class 1 for Physics 1A and Higher Physics 1A

Uncertainties Problem Solving class 1 for Physics 1A and Higher Physics 1A - PowerPoint Presentation

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Uploaded On 2018-03-23

Uncertainties Problem Solving class 1 for Physics 1A and Higher Physics 1A - PPT Presentation

What are problem solving classes These form a bridge between lecture material labs and the exam In some problem solving classes you will be introduced to material covered in the lab part of the course ID: 661729

errors uncertainties height uncertainty uncertainties errors uncertainty height lab ball physics percentage add random independent dependent absolute systematic error

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Slide1

Uncertainties

Problem Solving class 1 for Physics 1A and Higher Physics 1ASlide2

What are problem solving classes?

These form a bridge between lecture material, labs and the exam.

In some problem solving classes you will be introduced to material covered in the lab part of the course.

In all of them you will be practicing using the physics you have been shown in lectures to answer problems. This is a vital skill as this is what you will need to do in the exam.Slide3

Why are uncertainties important?

How long does it take the ball to reach the floor?

Are you certain?

If I dropped it from the same height would I get the same answer again?Slide4

Random uncertainties

We will usually be dealing with these in the lab.

Random uncertainties are as likely to be above the “correct” value as below them.

Another way to say this: Random uncertainties have a zero mean.For example: measuring your height with a ruler; the mass of the 50g masses in the lab.Slide5

Systematic Uncertainties

Used in the standing waves on a string experiment.

These uncertainties have a non-zero mean, they cause you to consistently measure an uncertainty that is too large or too small.

Can be caused by:Poor techniqueCalibration errorsZero errors

Standing wave in column with end effectsSlide6

Systematic or Random?

Is the error in the measurement

of the time it takes the ball to

fall using a stopwatch a systematic or a random error?SystematicRandomBothNeitherSlide7

How do you account for Systematic Uncertainties?Slide8

From now on we are considering Random uncertaintiesSlide9

Calculating the error in a measurement

In the first year physics lab we use:

More correct to use standard deviation. Slide10

Why don’t we use the standard deviation in the first year physics lab?

We are lazy

There is not enough time to collect enough data

Statistics is too hard for this courseWe should and I am going to use it in all the experimentsSlide11

Practice

Five people measure the height of a laboratory bench, they record it as 98.2, 99.1, 98.4, 100.3 and 98.5 cm high. What is the height of the bench with an uncertainty?

A. 98.9 ± 2.1 cm

B. 98.9 ± 1.0 cmC. 98.9 ± 1.1 cmD. 98.9 ± 1.05 cmSlide12

Dependent Errors

These come from the same source, for example if you use the same piece of equipment to make a measurement then the errors are dependant. Slide13

Independent Errors

These come from different sources. If two different pieces of equipment are used then the errors are independent.Slide14

Classify as independent or dependent

Height a ball bounces and the mass of the ball

Height a ball bounces and initial height of ball

The period of a pendulum and the length of a stringAcceleration of a cart and the mass of the cartPeriod for a collision and the maximum acceleration during a collisionWhat might you be investigating in each of these experiments?Slide15

Can all errors be classed as independent or dependent?

Yes

NoSlide16

Absolute and percentage uncertainties

These are two ways to present the uncertainty. In the first year physics lab you should present your final uncertainty as an absolute uncertainty.

Absolute uncertainty

, is the uncertainty in the value presented with the same units as the value:Percentage uncertainty is the percentage of the final value that the uncertainty has:Slide17

Calculating dependent uncertainties

If you add or subtract the values then you add the uncertainties

If you multiply or divide the values then you add the percentage errors to get the final percentage error Slide18

Calculating Independent Uncertainties

If you add or subtract the value then you add absolute errors in

quadrature

(use Pythagoras)If you multiply or divide the value then you add the percentage errors in quadratureSlide19

Turn to part 3 of Introductory Experimentation in your Lab Manual

Work together to practice

using uncertainties.Slide20