Bridges

Beam Bridge: A beam bridge is a rigid, horizontal structure that rests on two end supports, and carries traffic loads by acting structurally as a beam.

Suspencion Bridge Simple suspension bridges, for use by pedestrians and livestock, are still constructed, based upon the ancient Inca rope bridge.

Truss Brige
A truss bridge is a bridge composed of connected elements (typically straight) which may be stressed from tension, compression, or sometimes both in response to dynamic loads.

Cantilever Bridge A cantilever is a structure or beam that is unsupported at one end but supported at the other, like diving boards. This configuration made longer spans possible and wider clearance beneath.

Motor Boat

Principle: Conversion of the chemical energy (battery) into mechanical energy (rotation of the fan) which propels the boat forward. The rotation of the motor is transmitted to the axle using a pair of gears.

Applications:
Motor boats can be used as industrial vehicles. They can also be used as racing boats.

Items Required to make:
Fan made out of tin metal strip
Cycle spoke
A small Motor
Battery
Soap case box.
Dynamo Windmill is an example of dynamo which works on the same principle of conversion of mechanical energy into electrical energy. For this mechanical energy is wind energy.

There is lesser friction in water compared to land / roads.Design of propeller blades is an interesting field of research where the objective is to come up with more efficient and lighter models.