- #1
mechprog
- 27
- 0
Consider the body shown below
Now, if G be the centre of gravity (or centre of any parallel uniformly distributed body force), then we define its position by equating the moment of total weight by moments of elemental weights about the same point i.e.
[tex]\vec{r_{G}}\times W \vec{\epsilon_{g}}=\int\int\int_V \vec{r_P} \times dW \vec{\epsilon_{g}}[/tex]
or
[tex]\left(\vec{r_{G}}-\frac{1}{W}\int\int\int_V \vec{r_P}dW\right) \times\vec{\epsilon_{g}}=0[/tex]
which explicitly gives,
[tex]\vec{r_{G}}=\frac{1}{W}\int\int\int_V \vec{r_P} dW + \lambda \vec{\epsilon_{g}}[/tex]
Now the question is: how to do away with the [tex]\lambda[/tex](an arbitrary number)
Seeing the question physically, this ambiguity in definition of comes from the transmissibility of force (from the point of view of moment).
This can be removed (mathematically, making [tex]\lambda=0[/tex]) by using the fact that centre of gravity has no bindings for orientation of the body.
So, how can I rotate the body and reduce the line of gravity (as defined above) to a point.
Now, if G be the centre of gravity (or centre of any parallel uniformly distributed body force), then we define its position by equating the moment of total weight by moments of elemental weights about the same point i.e.
[tex]\vec{r_{G}}\times W \vec{\epsilon_{g}}=\int\int\int_V \vec{r_P} \times dW \vec{\epsilon_{g}}[/tex]
or
[tex]\left(\vec{r_{G}}-\frac{1}{W}\int\int\int_V \vec{r_P}dW\right) \times\vec{\epsilon_{g}}=0[/tex]
which explicitly gives,
[tex]\vec{r_{G}}=\frac{1}{W}\int\int\int_V \vec{r_P} dW + \lambda \vec{\epsilon_{g}}[/tex]
Now the question is: how to do away with the [tex]\lambda[/tex](an arbitrary number)
Seeing the question physically, this ambiguity in definition of comes from the transmissibility of force (from the point of view of moment).
This can be removed (mathematically, making [tex]\lambda=0[/tex]) by using the fact that centre of gravity has no bindings for orientation of the body.
So, how can I rotate the body and reduce the line of gravity (as defined above) to a point.