Simple harmonic motion problem involving matrices

In summary, the conversation discusses deriving the equations of motion for a system of two equal masses connected by springs to a wall. The masses are also connected to each other by identical springs. The conversation includes a diagram and mentions using Hooke's Law to determine the equations. The correct equations for mass one are given, but there is some confusion about how to include the third spring in the equations for mass two. The conversation concludes with a suggestion to redraw the free body diagram and rewrite the equations to properly account for all three springs.
  • #1
ABoul
28
0

Homework Statement


2 equal masses are joined together by a spring of stiffness k. each of the masses is then connected to a wall with an identical spring. derive the equations of motion in matrix form. (a diagam has 2 masses with x1 on top of the first mass and x2 on top of the second.)


Homework Equations


hooke's law: F = kx


The Attempt at a Solution


mass 1:

mx1'' = F(x2 - x1) - Fx1
mx2'' = Fx2 - F(x2 - x1)

^ are these correct?
 
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  • #2
Mass one looks good but mass two is off. What happened to your third spring ?
 
  • #3
Also, draw yourself a free body diagram.
 
  • #4
CFDFEAGURU said:
Mass one looks good but mass two is off. What happened to your third spring ?

CFDFEAGURU said:
Also, draw yourself a free body diagram.

i did. there are only 2 displacements (x1 and x2), right? the extension of the third spring is not kx2?
 
  • #5
There are only two equations, but you need to include the third spring. If the masses are going to move springs 1,2, and 3 have to move with them.
 
  • #6
CFDFEAGURU said:
There are only two equations, but you need to include the third spring. If the masses are going to move springs 1,2, and 3 have to move with them.

but each mass is connected to 2 springs. therefore each equation should only have 2 terms. the only mistake i can see with the second equation is that Fx2 (force from the THIRD spring) should be negative. oh, and sorry if i haven't been clear enough -- the diagram goes like this:

[wall] [spring] [mass 1] [spring] [mass 2] [spring] [wall]
 
Last edited:
  • #7
Mass one depends upon springs 1 and 2. Mass two depends on springs 2 and 3. Rewrite your equations and redraw your FOB.
 

1. What is simple harmonic motion?

Simple harmonic motion refers to the back-and-forth movement of an object that follows a specific pattern, where the object's acceleration is directly proportional to its displacement from a central equilibrium point.

2. How are matrices involved in simple harmonic motion problems?

Matrices are often used in simple harmonic motion problems because they allow for the representation of multiple variables and their relationships in a concise and organized manner. The use of matrices can also simplify the calculations involved in solving these problems.

3. How do you set up a matrix for a simple harmonic motion problem?

The matrix for a simple harmonic motion problem typically includes variables such as mass, spring constant, displacement, velocity, and acceleration. These variables are represented as columns in the matrix, and the equations for each variable are represented as rows. The coefficients of each variable in the equations are then placed in the corresponding column in the matrix.

4. How do you solve a simple harmonic motion problem using matrices?

To solve a simple harmonic motion problem using matrices, the matrix is first set up with the appropriate variables and equations. Then, the matrix is manipulated using algebraic operations to isolate the desired variable. Finally, the values for the remaining variables are substituted into the equations to obtain the solution.

5. What are the benefits of using matrices in simple harmonic motion problems?

Using matrices in simple harmonic motion problems can help organize and simplify the calculations involved. They also allow for the representation of multiple variables and their relationships in a concise manner. Additionally, matrices can be used to solve more complex problems that involve multiple equations and variables, making them a useful tool for scientists and engineers.

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