# Homework Help: Very simple spring constant questoin

1. Apr 2, 2009

### The thinker

Hi,

Spring constant for a vertical spring: k=mg/$$\Delta$$

Is it the same for a horizontal spring on a frictionless surface?

Thanks!

2. Apr 2, 2009

### Limecat

No. Horizontally, it's just F = kx.

3. Apr 2, 2009

### The thinker

Thanks

So the "a" in F=ma in the horizontal case is just whatever acceleration the mass is undergoing, rather than g?

4. Apr 2, 2009

### d_vsuresh

Yes,you are right.
During the horizontal motion

F= ma = kx

And during the vertical motion

F = mg = kx

If friction is taken into count that force also shall be taken into count.

5. Apr 2, 2009

### Dr.D

Newton's 2nd law says
Sum of Forces = m*a
not just F = m*a

When written as F = ma, this tends to neglect that it is the sum of all forces on the particle (Newton's 2nd law is for a particle).

Writing F = mg is prone to suggest errors. It is safer to write
W = m*g
as a reminder that it is the weight force specifically that is equal to mg.

I am continually amazed at the number of people I see posting here who want to confuse the F's in F = ma and F = mg by setting them equal to each other! There is a dangerous lack of thinking going on.