Wind-up Car with LED Headlights
Physical Principle: Energy transfer. Energy can be stored by winding a spring. Through a series of gears, this energy can be used to drive the car and, with the help of a motor, power LEDs.
Age Group: This toy is safe for all ages with no small exposed parts, but would probably be fun age 3-6.
Use: Winding the knob tightens the torsion spring. As the spring unwinds, one gear system spins the back axis, driving the car. Another gear system turns a motor shaft, which outputs electricity to two LEDs.
Origin of Idea: We played with wind up cars in class. I thought it would be cooler if the wind-up cars had head lights.
Concerns: White LEDs could be bought a dollar a piece in the right quantity. The motor could be bought for $2. Throw in the plastic shell, wheels and gears and call it an even $6. That's for a decent sized toy car. It would be made durable enough to withstand drops, but could be pried open with a screwdriver. Overall, a safe toy - the motor would never get too hot.