- #1
Xyius
- 508
- 4
I REALLY need help with this one guys! As of right now I believe I only need help with just the set up of the problem. The rest is just solving a differential equation and I assume the frequencies they want will just pop out.
Two identical springs and two identical masses are attached to a wall. (It then shows a picture of two springs attached to a wall horizontally.) Find the normal modes and show that the frequencies can be written as [itex]\frac{1}{2}\sqrt{\frac{k}{m}}\left( \sqrt{5} \pm 1 \right)[/itex]
That's the part I need help with!
I get confused on these coupled harmonic oscillator problems because I do not fully understand how they set up Newtons second law. This is my logic to the above problem.
So when mass 1 (The left most mass) is displaced to the left from its equilibrium position, a restoring force of [itex]-kx_1[/itex] is created by the spring. At the same time, the other spring was also stretched in response to the first spring stretching and it exerts a force on mass 1 of [itex]-k(x_1+x_2)[/itex]. Where [itex]x_1[/itex] and [itex]x_2[/itex] are the distances from their respective equilibrium.
So the DE for the first mass is..
[tex]m\ddot{x}=-2kx_1-kx_2[/tex]
I am confused on getting the second differential equation. I tried a few things but I kept getting solutions that weren't sinusoidal, but exponential since the roots weren't complex.
Can anyone help?
Homework Statement
Two identical springs and two identical masses are attached to a wall. (It then shows a picture of two springs attached to a wall horizontally.) Find the normal modes and show that the frequencies can be written as [itex]\frac{1}{2}\sqrt{\frac{k}{m}}\left( \sqrt{5} \pm 1 \right)[/itex]
Homework Equations
That's the part I need help with!
The Attempt at a Solution
I get confused on these coupled harmonic oscillator problems because I do not fully understand how they set up Newtons second law. This is my logic to the above problem.
So when mass 1 (The left most mass) is displaced to the left from its equilibrium position, a restoring force of [itex]-kx_1[/itex] is created by the spring. At the same time, the other spring was also stretched in response to the first spring stretching and it exerts a force on mass 1 of [itex]-k(x_1+x_2)[/itex]. Where [itex]x_1[/itex] and [itex]x_2[/itex] are the distances from their respective equilibrium.
So the DE for the first mass is..
[tex]m\ddot{x}=-2kx_1-kx_2[/tex]
I am confused on getting the second differential equation. I tried a few things but I kept getting solutions that weren't sinusoidal, but exponential since the roots weren't complex.
Can anyone help?