Thanks for your reply,
The discussion you shared is very informative.
In order to prevent alias, the sampling rate must be set to very high.
Therefore, I have increased my output point to 5000.
However, there is still some discrepancy from the data I got from these 2 methods:
1) differentiate the velocity/time data, apply low pass filter
2) directly apply low pass filter to the directional acceleration
Acceleration got from Method 1 is closer to experimental data.
Could you explain the discrepancy of the data between these 2 method? which are the correct method of obtaining acceleration?