I'm doing a physics presentation on a hobby of mine. For my hobby I picked playing video games (my PSP). I thought it would be cool if I could calculate the amount of force/work I use to press a button on my PSP. I have no idea how I would do that. I know F=m*a and W=F*d

How would I go about doing this?

## Answers (2)

Construct a paper cup so that the base of the cup just covers the area of the button surface.

Place it over the button and add sand slowly to the cup so that the button is pressed .

Measure the mass of the cup with sand using a electronic balance which can measure milligram accurately.

The force needed is mg . Calculate. it Repeat a number of time and find the average force needed .

Good job.

You need to know the spring stiffness constant (k) for the resetting springs of the buttons.

Usually, measuring that also requires measuring a force, and measuring known deformation of the spring. The spring constant is the measure of stiffness that indicates how much extra force must be added for each additional deformation distance of the spring.

Button springs are often precompressed, even when the button isn't pressed. This will add complexity, because the spring might not start out relaxed. You'll need to measure (distance, force) at two different configurations, and extrapolate how much distance the spring is precompressed.

To calculate work, you'll need to either integrate Hooke's law, or use the already-done-for-you formula of SPE = 1/2*k*x^2. That means, the energy stored in the spring (strain potential energy) is given in terms of the spring constant k and the distance that the spring is deformed from its relaxed position (x). The value of x can ONLY be zero at the condition of a relaxed spring.

To calculate work done against a spring while compressing it between two compressed states will require a subtraction of two SPE calculations for the spring.

The formula W=F*d is only valid if the force is constant at every given position. Spring forces ARE NOT constant, but they differ for every different strain of the spring.

The formula F=m*a is very little help at all, because I doubt you will have the patience to put a tiny accelerometer on the buttons and analyze the data of acceleration.