Moment of inertia of 2 uniform thin rods

In summary, the moment of inertia for 2 uniform thin rods about axis A can be calculated using the parallel axis theorem, which states that the moment of inertia is equal to the sum of the moment of inertia about the center of mass and the product of the mass and the square of the distance between the center of mass and the axis of rotation. In this case, the distance, d, can be calculated using the formula ##d = \sqrt{(\frac{3}{9}L)^2 + (0.5L)^2}## for the top rod and ##d = 0.5L - \frac{4}{9}L## for the bottom rod.
  • #1
jisbon
476
30
Homework Statement
Calculate the moment of inertia of 2 uniform thin rods about axis A where the figure belows shows the top view.
Relevant Equations
##I=\frac{1}{12}ml^2##
1571734403087.png


So to start off, what I will do find the center of mass of each of the rods. So for the top rod, COM is at where y= 0.5 L and COM of the rod at the bottom is at x = 0.5 L. From there, how do I proceed in finding the moment of inertia using parallel axis theorem? Do I simply treat:
##I =\frac{1}{12}ml^2+md^2##
Where d is the distance between the centre of mass and point A for each of the rods respectively? (Whereby d will be 0.5 L - 4/9 L for the bottom rod)

Thanks
 
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  • #2
jisbon said:
Homework Statement: Calculate the moment of inertia of 2 uniform thin rods about axis A where the figure belows shows the top view.
Homework Equations: ##I=\frac{1}{12}ml^2##

View attachment 251651

So to start off, what I will do find the center of mass of each of the rods. So for the top rod, COM is at where y= 0.5 L and COM of the rod at the bottom is at x = 0.5 L. From there, how do I proceed in finding the moment of inertia using parallel axis theorem? Do I simply treat:
##I =\frac{1}{12}ml^2+md^2##
Where d is the distance between the centre of mass and point A for each of the rods respectively? (Whereby d will be 0.5 L - 4/9 L for the bottom rod)

Thanks
Yes. What will d be for the other rod?
 
  • #3
haruspex said:
Yes. What will d be for the other rod?
Will it be ##\sqrt(({\frac{3}{9}L)}^2+(0.5L)^2)##?
 
  • #4
Solved it. Thanks so much for your guidance 😄
 

1. What is the definition of moment of inertia?

The moment of inertia is a physical property of an object that describes its resistance to rotational motion. It is the measure of an object's tendency to resist changes in its rotational velocity.

2. How is moment of inertia calculated for two uniform thin rods?

To calculate the moment of inertia for two uniform thin rods, you can use the formula I = ½ ML², where I is the moment of inertia, M is the mass of the object, and L is the length of the object.

3. What factors affect the moment of inertia of two uniform thin rods?

The moment of inertia of two uniform thin rods is affected by their mass, length, and distribution of mass. The farther the mass is from the axis of rotation, the larger the moment of inertia will be.

4. How does the moment of inertia of two uniform thin rods compare to that of a single rod?

The moment of inertia of two uniform thin rods is greater than that of a single rod because the combined mass and distribution of mass create a larger resistance to rotational motion.

5. Why is the moment of inertia important in rotational motion?

The moment of inertia is important in rotational motion because it determines the amount of torque needed to produce a given angular acceleration. It also plays a role in the conservation of angular momentum, which is an important principle in physics.

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