Advanced Automatic Control Systems 04/3

T H E U N I V E R S I T Y O F L A H O R E

Cont. (Understanding FBD*)

To understand the direction of terms and forces, take the case of spring K2,

1. Assume at first that M2 is stationary and M1 is moving with a displacement of x1(t).

• This motion would cause K2 to compress generating a force K2 x1(t) in a direction opposite to x1(t).

2. Now assume that M1 is stationary and M2 is moving with a displacement of x2(t).

• This motion would cause K2 to elongate generating a force K2 x2(t) in a direction of x2(t).

𝑥𝑥1

𝐾𝐾2𝑥𝑥1(𝑡𝑡)𝑀𝑀1

𝐾𝐾2𝑥𝑥2(𝑡𝑡)

*FBD = Free Body Diagram