Watering plants in terracotta pots is a hugely water inefficient as well as time-consuming. Water is lost due to evaporation from the soil and through the terracotta as well as running out through the bottom of the pot. There are better systems available and we will consider three types:
You could just set up all three systems and use trial and error in order to optimise them. They are, however, likely to be successful if we use the Scientific Design Thinking approach. Here we will look at the science behind them and how we can use this knowledge to make predictions and learn new concepts.
Pressure in a Fluid – What might happen to the water if we had holes in a bottle?
A bottle has three holes above one another in its side. How will the water flow out of the bottle when the lid is opened? A, B or C?
You may want to watch this video (or read below) to help you decide
Answer
(C) A higher pressure would lead to the water squirting out further. You can see this by squirting water in your mouth out through a straw. The higher the pressure you exert, the further the water goes.
The deeper you go in a fluid the higher the pressure gets due to the weight of all of the molecules above. Deep sea fish have adaptations in order to survive these massive pressures. Similarly, we live at the bottom of an ocean of air. Above you is about 100km of air molecules and the combined weight of all of these is about the same as having a small car on your head. If you didnt also have air inside your body balancing these forces you would be crushed.
Possible experiment: How does the rate of water flow change as the bottle empties?
What might happen if the hole size was different but the pressure was the same?
Would you see (A) (B) or (C)?
Make a prediction and justify it
Answer:
Possible experiment: How does the diameter of the hole affect the rate of water flow from the bottle?
So far we have two factors that affect the rate that plants would get water. The height of the water column and the size of the hole or holes.
(1) Make a Drip Bottle Watering System
So here is a bottle with a hole in the lid hanging upside down. What will happen?
What happens if you take the lid off? Why?
Possible experiment: What is the maximum size of hole in the lid so that water does not flow out of the bottle when turned upside down?
Watch the video
Challenge: Make your bottle take an hour to empty
How can you regulate the flow? What might happen if …..
What might happen if:
Some questions:
Using this principle we can have several bottles filling a tray of water. We can add nutrients to these bottles in the form of Compost Tea or fertilizer.
To prevent the plants being waterlogged, capillary matting can be used or layers of cloth that absorb moisture. Covering the tray with a waterproof lid will reduce water loss by evaporation.
You could just set up all three systems and use trial and error in order to optimise them. They are, however, likely to be successful if we use the Scientific Design Thinking approach. Here we will look at the science behind them and how we can use this knowledge to make predictions and learn new concepts.
Pressure in a Fluid – What might happen to the water if we had holes in a bottle?
A bottle has three holes above one another in its side. How will the water flow out of the bottle when the lid is opened? A, B or C?
You may want to watch this video (or read below) to help you decide
Answer
(C) A higher pressure would lead to the water squirting out further. You can see this by squirting water in your mouth out through a straw. The higher the pressure you exert, the further the water goes.
The deeper you go in a fluid the higher the pressure gets due to the weight of all of the molecules above. Deep sea fish have adaptations in order to survive these massive pressures. Similarly, we live at the bottom of an ocean of air. Above you is about 100km of air molecules and the combined weight of all of these is about the same as having a small car on your head. If you didnt also have air inside your body balancing these forces you would be crushed.
Possible experiment: How does the rate of water flow change as the bottle empties?
What might happen if the hole size was different but the pressure was the same?
Would you see (A) (B) or (C)?
Make a prediction and justify it
Answer:
Possible experiment: How does the diameter of the hole affect the rate of water flow from the bottle?
So far we have two factors that affect the rate that plants would get water. The height of the water column and the size of the hole or holes.
(1) Make a Drip Bottle Watering System
So here is a bottle with a hole in the lid hanging upside down. What will happen?
What happens if you take the lid off? Why?
Possible experiment: What is the maximum size of hole in the lid so that water does not flow out of the bottle when turned upside down?
Watch the video
Challenge: Make your bottle take an hour to empty
How can you regulate the flow? What might happen if …..
- The hole in the lid is made bigger or smaller?
- A hole is made at the top of the bottle? How might the size of this hole affect the flow rate?
- Sand/cotton string is used to restrict the flow through the bottle?
- A sports bottle top is used?
What might happen if:
- We changed the number of holes?
- We changed the pattern of holes? Should there be more at the top and fewer at the bottom?
- We changed the size of the holes?
- Does the bottle drain at different rates in soil than in air?
- Does it make a difference if the soil is wet or dry?
- How can we use this to water plants more effectively?
Some questions:
- What combination of bottle sizes works best?
- How many plants can be grown in the big bottle?
Using this principle we can have several bottles filling a tray of water. We can add nutrients to these bottles in the form of Compost Tea or fertilizer.
To prevent the plants being waterlogged, capillary matting can be used or layers of cloth that absorb moisture. Covering the tray with a waterproof lid will reduce water loss by evaporation.