What it shows
A DC motor turns electrical energy into rotation. Angled blades cut from a bottle push air backwards as they turn, so a breeze comes forward, and a switch in the circuit starts and stops the fan.
The science
When the switch is closed the cells push current through the motor coil, which sits in a magnetic field, so a force turns the shaft. The propeller blades are twisted at an angle, so as they sweep round they deflect air backwards; by Newton’s third law the air pushes the blades forward, and the fan blows a breeze towards you. Reversing the battery leads reverses the motor and the blade angle then pushes air the other way, so the fan sucks instead of blows.
Materials
Cost: under Rs 100. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A 3 V DC toy motor
- A plastic bottle (for the propeller) and its cap
- A 2 x AA battery holder with cells (3 V)
- A slide switch or a paper clip switch
- Cardboard for the stand and base
- Hot glue, scissors and insulated wire
Safety
For this project: An adult must cut the bottle and use the hot glue gun. Keep fingers and hair away from the spinning blades.
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.
Step 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.
Cut the bottom quarter off the bottle and cut four equal blades from the curved side, leaving them joined at the cap end.
Twist each blade a little in the same direction and push the cap onto the motor shaft with a drop of hot glue.
Cut a cardboard stand with a hole for the motor and glue it onto a wide cardboard base so it cannot tip.
Glue the motor into the stand with the propeller pointing forward and clear of the base.
Wire the battery holder red lead to one side of the switch, and the other side of the switch to one motor terminal.
Wire the other motor terminal back to the battery holder black lead.
Switch on: the propeller spins and you feel a breeze. If air blows backwards, swap the two motor wires.
Hold a strip of tissue in front and behind to show which way the air moves.
What you should see
The fan spins when switched on, blows a breeze that moves a tissue strip, and reverses when the motor leads are swapped.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why do the blades need a twist?
Flat blades just stir the air; angled blades push it in one direction.
02What happens if you swap the battery wires?
The motor turns the other way and the fan blows backwards.
03Why not use a 9 V battery for a faster fan?
A 3 V toy motor would overheat and burn out at 9 V.
04Name the energy changes in the fan.
Chemical to electrical in the cells, electrical to kinetic in the motor and the air.
Take it further
Add a second battery holder and a selector switch so the fan has a slow (3 V) and a fast (4.5 V) setting.
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
Robotics
Motors, Gears and Motor Drivers
Make things move: DC motors, servos, steppers and how to drive them
Science projects
Best Out of Waste Science Projects
Working models from bottles, cardboard, CDs and old parts
Find out more about electronics and robotics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.