This project is too old but recently I get chance to make it again. It was my friend’s requirement for science exhibition. He just want to participate so want a simple low cost project. I already did this project in 1998 when I was in school (only difference was I did this with IV bag and now did with tire’s tube). It require almost 2 hrs to make and calibration.

This based on Archimedes principle of buoyancy, it is not clearly uses this principle as forces are affected by other things also. It works in partially closed system and shows exact result.(+-1%). In simple way just fill tire tube with water so when some force applied over tube then water come out of tube will be equal to magnitude of force.
Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces. Archimedes' principleis a law of physics fundamental to fluid mechanics. For more info please visit

https://en.wikipedia.org/wiki/Archimedes'_principle

This project mainly contains work with water so I am missing some photos but still it will give you proper idea.

Step 1: Material Required

Material

required:

Old tire tube (12”dia)

¼” ID transparent tube- 7’ long

A syringe

Some food color

Some ¼” thick plywood

Paper

Marker

Water cans and bottles for calibration

Step 2: Tube Preparation

I used a Riksha’s scrap tire tube, as it is easily available for me, you can use any tube of dia around 12”.

Remove valve from tube. To remove it you can use dedicated driver, in my case I used a U clip. Just open U clip and insert open ends in valve and rotate it anticlockwise, that’s all the valve seat will come out.

Now take syringe and start filling water in tube. As this tube have only one valve, it is very difficult to out all air. Our tube accommodates almost 4.5 liter water.

Step 3: Final Attachments

Now attach transparent tube to valve and some liquid food color in tube. Now our project is ready for calibration.

I also made a tube frame to accommodate and guide tube. So when we stand over tube, it will not unbalance us. Frame supplied with 04 rod at each end, these rods guides plywood in single direction. And below pad 12” dia cardboard keep to equal load distribution.

Step 4: Calibration

For calibration we used 20 liter water drums(4nos) and some 1 liter bottles(20 nos), both are first calibrated with digital weigh scale.

We started our calibration with trial and error method.

Keep tire’s tube horizontal and stick transparent tube to wall vertically.

Then added 20 kg weight and mark it on transparent tube.

Then keep adding 1 kg weight and marking on transparent tube.

Continue marking till 80 kg weight.

So finally we will get calibrated scale. and when someone stand over tube then water will show calibrated weight marking which will be almost perfect.