What it shows
A covered, ventilated box dries food faster and cleaner than open-air drying. Weighing equal slices each day shows how quickly water leaves in each method.
The science
Drying removes water by evaporation, which is fast when the air is warm, dry and moving. The black floor and clear lid heat the air inside the box, and holes let moist air out and fresh air in. The closed box also keeps dust, flies and rain off the food.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A cardboard or wooden box about 40 cm by 30 cm
- Clear plastic sheet for the lid
- Black paper for the floor
- Thin net or mesh trays
- Banana, mango or chilli slices
- A kitchen scale (0.1 g if possible)
- A few small holes for air
Safety
For this project: An adult must slice the food with a knife and handle chillies; wear gloves and do not touch eyes. Do not eat food dried in an experiment with other materials; use clean food only for a separate batch.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Paint or line the box floor with black paper and cover the top with clear plastic.
Make two rows of small holes near the bottom front and top back to let air flow through.
Cut equal slices of fruit and weigh two matching trays, noting each mass.
Place one tray in the box and the other in the open on a plate in the same sun.
Weigh each tray at the same time every day for three days.
Record the mass of each tray and work out the percentage of water lost.
Observe colour, smell and any insects or mould in the two samples.
Plot mass against time for both trays and compare drying rates.
What you should see
The tray inside the cabinet loses mass faster and stays cleaner than the open tray. Graphs show a steeper fall for the cabinet.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does drying keep food from spoiling?
Microbes need water to grow.
2Why make air holes?
Moist air must leave, or drying slows down.
3Why weigh at the same time daily?
To keep the conditions comparable.
4How could farmers use this?
To dry grain, spices and fruit hygienically without fuel.
Take it further
Add a second black metal sheet as an absorber and see if the drying time drops further.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Investigatory Projects for Class 11 and 12
Topics, method and report structure for physics, chemistry and biology