# Rubber band Calculation- Urgent

1. Jun 5, 2014

### choudhari.mayu

Hello i need to know what should i do,

Consider i have a box, top half and bottom half. so now i have to hold the top half and bottom half together with the rubber band then how do i know what rubber band will be enough to exert force so that both parts of box are hold together.

also i dont want the box to deform more then 1mm due to rubber band force, from the force gauge i see that it requires 0.067 bar to deform box by 1mm.

Also there is a mass in box weighing 5 kg. so now to hold the two box parts with 5 kg mass when i am lifting the box just with the top half of box. How do i select the rubber band? how do i determine the force it should exert on the box to hold it together without deforming box more than 1mm.

Rubber band calculations any? Any place i could find any references or formula for something like this. you help is appreciated.

2. Jun 5, 2014

### mathman

If this is a real concern, I suggest trial and error.

3. Jun 5, 2014

### choudhari.mayu

I cant do trial and error also by any chance does any one know from standard rubber band sizes what force is exerted by the specific rubber band.

4. Jun 6, 2014

### 256bits

You say you don't want the box to deform, yet want to lift by the top with a 5kg weight inside.

You can calculate the minimum width of the band so that when lifting the box by the top, the bottom will not have a pressure above your force gauge figure. Most of the force and pressure will be at the corners when the band meets the bottom ( and NOT the whole area of the band covering the bottom). You will have to estimate that area, so that the corner does not crinkle.

I also assume you have taken into account of deflection the bottom area will have by supporting a 5 kg mass. Is that less or more than your 1 mm force gauge deflection.

5. Jun 6, 2014

### rcgldr

I use latex rubber tubing for launching radio control model gliders. I use different diameter tubing depending on the weight of the model I'm trying to launch. Here are some sample data points for strain versus tension, based on the unstretched cross-sectional area of the tubing. Note that a strain of 100% means the total length of the tubing has been doubled from it's original length. As an example, 300% strain with 60 feet of tubing means that one end of the tubing was pulled 180 feet away from it's original position, increasing the total distance of the tubing to 240 feet. At around 400% strain, some permanent deformation takes place, so it's not recommended. 350% or less hasn't resulted in any noticable permanent effect.

Code (Text):

strain    tension
0% =   0 lb / in^2
50% =  70 lb / in^2
100% =  95 lb / in^2
150% = 115 lb / in^2
200% = 135 lb / in^2
250% = 160 lb / in^2
300% = 175 lb / in^2
350% = 195 lb / in^2
400% = 205 lb / in^2  (not recommended).

The issue with a rubber band is there is a limited choice of lenghts and cross-sectional area. You could use multiple rubber bands to spread out the load.

Last edited: Jun 6, 2014
6. Jun 6, 2014