- #1
cupid.callin said:the density you used is defined from the lighter end and you have to find I about heavier end.
you may take the dx element at distance x from heavy end and then use (10-x) in the equation of density
athrun200 said:Is it a rule that I must start from heavy end?
Why it is wrong to start from light end?
gneill said:It's not a rule, and it's not wrong to start at the light end. You may start anywhere you wish! But note that the problem is asking for the moment of inertia about the heavy end. Therefore, in the the calculation of the moment of inertia, the radial distances of the mass elements must be with respect to the heavy end. And be sure that the density at that distance from the heavy end is the correct density for that position along the rod.
gneill said:Suppose you break the integral into two. The first runs from x=0 to x= xcm, the second from xcm to 10. The density function remains as 2x + 4 for any value of x, so leave it alone. What is the distance from xcm to the mass element in each case?
athrun200 said:I am so sorry that I don't understand.
Can you explain it more clearly?:shy:
gneill said:
x is the position along the rod from the LHS. For the region to the left of the center of mass, the distance from the center of mass to x is xcm - x. To the right of the center of mass, the distance is x - xcm. The density at point x remains [itex] \rho (x) = 2 x + 4[/itex], since here x is always with respect to the light end of the rod.
athrun200 said:Oh! It works and I get the answer!
But can you explain what's wrong with my method?
Why I can't set the center of mass as the orgin?
athrun200 said:Work in #6 turns out to be correct, I just type it wrongly in my calculator.
By the way, how to generate the picture in #9?
What software are you using?
Moment of inertia is a measure of an object's resistance to changes in its rotational motion. It depends on the mass and distribution of mass of the object.
Moment of inertia is calculated by multiplying the mass of each individual particle in the object by the square of its distance from the axis of rotation, and then adding all of these values together.
Moment of inertia is important because it helps to analyze and predict an object's rotational motion. It is also used in engineering and design to determine the strength and stability of structures.
The two main factors that affect moment of inertia are the mass and distribution of mass of the object. Objects with larger masses or mass concentrated farther from the axis of rotation will have a higher moment of inertia.
Moment of inertia and mass are related but different concepts. Mass is a measure of an object's resistance to linear motion, while moment of inertia is a measure of an object's resistance to rotational motion. In other words, mass determines how difficult it is to accelerate an object, while moment of inertia determines how difficult it is to rotate an object.