# Accuracy and Precision

To find out how accurate a stop clock, ticker timer and light gate are, and therefore how precise my work is.

Definitions:

Accurate – free from error

Precise – exact; correct and clearly stated

Apparatus:

* Trolley

* Runway

* Blocks

* Stop clock

* Ticker timer

* Tick tape

* Power pack

* Meter rule

* Light Gate

* Cardboard

* Balance

Diagram:

Method:

1. Collect and set up apparatus.

2. Weigh trolley, record.

3. Raise runway to 15cm high.

4. Measure 1.00m on runway.

5. Place Trolley at top of runway.

6. Release trolley and start Stop clock.

7. Stop clock when trolley past 1.00m.

8. Repeat 3 times and record results.

9. Attach 1.00m length of ticker tape to back of trolley.

10. Turn ticker timer on and release trolley.

11. Repeat 3 times and record results.

12. Tape piece of card to top of trolley, and reweigh trolley, record.

13. Turn light gate on, make sure 1.00m apart.

14. Release trolley with card, to register with light gate.

15. Repeat 3 times and record results.

Results Table:

Time (s)

1

Time (s)

2

Time (s)

3

Time (s)

Avg

Mass

(kg)

Dist

(m)

V

(ms-1)

Avg

V

(ms-1)

max

a

(ms-2)

F

(N)

Stop clock

1.8

1.9

1.9

1.9

0.783

1.00

0.53

1.1

0.28

0.227

Ticker timer

1.7

2.0

2.2

2.0

0.783

1.00

0.51

1.0

0.26

0.203

Light Gate

1.74

1.72

1.70

1.72

0.811

1.00

0.58

1.2

0.34

0.276

Formulae used:

* S = d/t

* V max = 2V

* F = m a

* a = (V – u)/t

* T avg = (T1 + T2 + T3)/3

Calculations:

S = d/t

S = 1.00/1.9

S = 0.53

V max = 2V

V max = 2 * 0.51

V max = 1.0

F = m a

F = 0.811 * 0.34

F = 0.276

a = (V – u)/t

a = 0.53/1.9

a = 0.28

Observations:

I noticed that when we did the ticker timer experiment that the tape gave the trolley extra friction by pulling on it as it went down the runway. Also with this experiment when it came to counting up the dots on the tape you would get a dot and a half on the end of the tape, and not include the half. This would make your results less accurate.

With the light gate experiment, the trolley was heavier as it had a piece of card on top of it so that it could register with the light gate. As it had this extra weight, the trolley swerved when we let it go, this meant the trolley travelled further.

When we did the stop clock experiment, I noticed that when the person pressed the stop clock, there was a reaction time, which would make the times less accurate.

Conclusion:

I thought that the stop clock experiment was the least accurate of all the experiments. I thought this, as it seemed to have the most errors. You had the reaction times of the start and stop of the stop clock, which would have made the results inaccurate. You also had to take into account that the timer did give the results to 1/100th of a second, which is very accurate, but you have to see that the reaction time means that you should only take your results to 1/10th of a second. Although all of this is true, the stop clock method was the purest of all the experiments, as it did not have anything affecting the way the trolley rolled.

The ticker timer experiment was still not quite accurate. It had a few errors as well. When the trolley was let go there was friction from the tape as it went through the ticker timer. This would have slowed the trolley down, and made our results inaccurate. Also the tape was 1.00m long, and you would count up all the dots on this. If at the end of the tape there was about a cm without a dot, or maybe more then that, you would not include it, so it was not very accurate in that respect.

The light gate was the most accurate experiment, but it still had a few errors. The trolley was a lot heavier as it had the cardboard on top of it, so this would have slowed it down a bit as there would have been more friction between the runway and the trolley. Also as the cardboard weighed it down on one side, the trolley would swerve to one side, so it actually travelled further. It was the most accurate as it was measured by a computer, and to 1/100th of a second. Making it more precise as well.

Evaluation:

Overall I think that this experiment went quite well. The times that we got were fairly accurate, and they were not that far apart. If I had to do this experiment again, I would change a few things that I did. I would try to do all the experiments at once, so that if something affects one thing, it should affect them all, and you would be able to see how accurate or inaccurate the results were, as they should all be the same.