Transcript Estimating Gravity

Estimate “g”
Physics – Acceleration – Finding “g”
What is Gravity?
Gravity is an accelerating force which always acts towards the centre of an
object and is directly related to the amount of matter or mass that an object
has. Newton's 3rd Law of uniformly accelerated motion and experimentation
helps us understand how it effects mass. The law applies in this case to a
falling object i.e. ball falling to the earth with a starting velocity; u = 0 ms-1.
The only accelerating force is gravity and the time taken for the drop is t.
s = ut+½at2
s = 0+ ½ at2
From this we can
work out g by
graphing s against t2.
s = ½ gt2
(2/g)s = t2
NB: in this case “g” is taken as having positive effect
“s” or displacement is also positive.
Newton's 3rd Law of Uniformly
Accelerated Motion
s = ut+½at2
s = 0+ ½ at2
s = - ½ gt2
(2/g)s = t2
Hence if w plot a line graph to fit the
principle y = mx + c
y = vertical axis (t2)
x = horizontal axis (s)
m = gradient. (2/g)
c=intercept (zero in this case or a
systematic error)
We can say
2/g = grad or 2/grad = g
By taking the LOBF as drawn this
experiment calculated g = 10.78 ms-2
 10 ms-2
Distance in m
(0.002m)
Time Taken Squared in s2
( 0.020 s2)
Time Taken in s ( 0.010 s)
Small Ball
Large Ball
Small Ball
Large Ball
0.411
0.2736
0.2703
0.075
0.073
0.343
0.2566
0.2464
0.066
0.061
0.264
0.2320
0.2329
0.054
0.054
0.193
0.1856
0.1809
0.034
0.033
0.105
0.0150
0.1302
0.000
0.017
(2/g)s = t2
Hence if we plot a line graph to fit the principle y = mx +
c
y = vertical axis (t2)
x = horizontal axis (s)
m = gradient. (2/g)
c=intercept (zero in this case or a systematic error)
We can say
2/g = grad or 2/grad = g