What it shows
A small steel ball rolls to the low end of a tube when it is tilted and bridges two bare wires there. This completes a circuit, so the object is warned when it moves out of the upright position.
The science
When the tube is level or upright the ball sits at one end, away from the wires, so the circuit is open. When the tube tilts, gravity makes the ball roll to the lower end where two bare wire tips are close together. The conducting steel ball touches both wires at once and completes the circuit, so current flows through the buzzer. This is the idea of a mercury tilt switch without the poisonous mercury.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A stiff plastic drinking straw or an empty pen refill tube, about 8 cm
- A small steel ball (from a broken bearing) or a bicycle ball bearing
- Two 12 cm bare ended wires
- A 3 V active buzzer
- A 2 x AA battery holder with two cells
- A small box, glue and tape
Safety
For this project: Cells only. The ball is a small part: keep it away from young children and do not put it in your mouth.
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.
Push the two bare wire ends into one end of the straw, side by side, about 2 mm apart, and tape them in place.
Drop the steel ball in so it can roll freely, and plug the other end of the straw with a piece of paper or tape.
Test by rolling the ball to the wire end: check with a continuity test or by connecting the battery.
Connect one wire from the straw to the buzzer red lead.
Connect the buzzer black lead to the battery holder black wire.
Connect the battery holder red wire to the other straw wire.
Fix the straw standing upright in the box with the wire end at the top, so the ball rests at the bottom.
Tip the box more than about 45 degrees and the ball rolls onto the wires; the buzzer sounds. Return the box upright to stop it.
What you should see
The buzzer sounds when the box is tilted past a set angle and stops when it is upright again.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What closes the circuit?
The steel ball touching both wires, because steel conducts electricity.
2Why does the ball roll?
Gravity pulls it down to the lowest end of the tube.
3How can you change the tilt angle needed?
Move the wires further down the tube or lengthen the tube.
4Where is a tilt switch used?
In bag alarms, toys, some washing machines and heaters that shut off if tipped.
Take it further
Fix the box on a toy bicycle to make a fall detector.
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
Science Projects for Class 6 to 8
Working models matched to middle-school science topics