# Homework Help: Hooke's Law Trouble

1. Dec 1, 2014

### garr6120

1. The problem statement, all variables and given/known data
i am doing this hooke's law lab to figure out a spring's force constant. I am plotting Force vs. Extension on a graph and then i can calculate the k value using slope however, i keep getting a quadratic instead of a linear line.

2. Relevant equations

3. The attempt at a solution
I found out the values for my force but multiplying the mass of the weight on the spring by the force of gravity; 9.81 m/s^2. i then had to calculate my extension which i calculated by subtracting the masses extension of the spring by the equilibrium position. Here is a table of values to show you:
mass (kg) Extension (m) Force (N)
0.0 0.000 0.0000
0.1 0.008 0.0008
0.2 0.010 0.0020
0.3 0.015 0.0045
0.4 0.021 0.0084
0.6 0.026 0.0156
0.8 0.032 0.0256
1.0 0.041 0.0410

2. Dec 1, 2014

### SteamKing

Staff Emeritus
There's something about your table which is confusing. If the mass = 1.0 kg, shouldn't the force acting on the spring be 9.8 N approximately? How come your table indicates the force is 0.041 N?

Similarly, if the mass = 0.1 kg, shouldn't the force be 10% of that for a mass of 1.0 kg? How did you get 0.0008 N?

3. Dec 1, 2014

### Bystander

You show three columns of numbers. Which column is what?

4. Dec 1, 2014

### garr6120

ya sorry steamking i don't know why but i put my force into excel so that my mass would multiply by my extension instead of the force of gravity oops. one more question does 215.4 N/m sound right based on this data?

5. Dec 1, 2014

### SteamKing

Staff Emeritus
Why don't you show your calculation of this value?

6. Dec 1, 2014

### garr6120

On the graph that i created i used the points (0, 0) and (0.039, 8.4000). I put these into the slope equation $\frac{force_2-force_1}{extension_2-extension_1}$, $\frac{8.4000 N-0.0000 N}{0.039 m-0.000 m}$ therefore, $k=214.4 \frac{N}{m}$

7. Dec 1, 2014

### SteamKing

Staff Emeritus
Why did you throw out the last reading when the mass = 1.0 kg?