# Physics Practical Moments - sacss-science-physics by hcj

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```									Physics Practical
Determine acceleration of free fall
using spiral spring
• Position of hanger without mass must be larger than
position of hanger with mass (base on diagram)
• E = difference between the 2 readings
• *Must convert to mm correctly
• Difference between                     • T calculated correctly
first and second                         (i.e. average / 20) &
timing cannot be     • Average         • T given to 3 sf [1]
Interval of 50 g     more than 1 s. [1]     calculated
[1]                                   correctly and   • T2 calculated
given to 2 dp     correctly & T2 given
[1]               to 2 dp [1]
Graph Plotting

A – Axis labelled correctly with quantity / unit

P – Points plotted accurately and with a neat x

L – Line of best fit is drawn
* equal distribution of points above and below the line, line is
not too thick
* follow trend instead of trying to pass through all the
points

S – Correct scale is used
* more than ½ of the grid is used by the plotted points
* no awkward scale like 3 cm rep 2 mm or 2 cm rep 3
degrees etc is used
(i)     Measure the gradient of the line, showing clearly on your graph
how you did this.

Gradient = y2 – y1 = 0.60 – 0.35         = 0.25 / 155 = 0.00161
x 2 – x1  325 - 170

Must show
•Working on the graph (big dotted triangle with
coordinates labelled)
•Formula of gradient
•Substitution
•final ans to 3 s.f.
(ii)     Use the gradient from (i) and the extension, E, from (4) to find the
value of g, using the following formula.

Must show
•substitution
•final ans to 3 s.f.

g between 9 to 11
(iii)   What are the units of your value of g?   [0.2 is a constant
which has a unit of 1/g.]

m/s2
(iv) State a precaution that you have taken to increase the
accuracy of the experiment.[1]

Ensure that the oscillation is steady before timing to ensure that the
period for every oscillation is consistent.
Or
Ensure that the spring oscillates up and down only, reject timing if it
oscillate in 2 or 3 dimensions to ensure that the period for every
oscillation is consistent.

When stating precaution,
-Be specific on what is done, do not give general comments like
‘avoid parallax error’;
-Do not repeat the steps already stated in the procedure (e.g.
repeat the experiment and find the average to reduce random
error caused by human reaction time);
-state what is being done and why it is necessary to do it.

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