Simple Pendulum: 
Calculating Earth’s Gravity By Using a Basic Pendulum

 

Gravity Experimental
# of Revolutions Time Length T Period  Time / # of Rev. Pie Experimental Gravity = 4*(pie^2) *L / (T^2) Accepted Gravity  9.81 m/s^2 or 981 cm/s^2 Percent Error
25.5 29.7 30.4   3.14   981  
26 29.9 30.4   3.14   981  
25 28.4 30.4   3.14   981  
10 13.2 30.3   3.14   981  
15 16.2 30.3   3.14   981  
20 22.1 30.3   3.14   981  
13 14.9 30.9   3.14   981  
10 11.9 30.9   3.14   981  
8 10.1 30.9   3.14   981  
30 21.9 31.3   3.14   981  
40 31.9 31.3   3.14   981  
50 42.9 31.3   3.14   981  
21 23.4 31   3.14   981  
31 34.15 31   3.14   981  
15 16.35 31   3.14   981  
31 36.94 30.4   3.14   981  
17 18.8 30.4   3.14   981  
10 12.66 30.4   3.14   981