Question

Why army trucks weight more than one thousand tonnes rest upon a continuous chain
A truck has much wider tyres
Cutting tools have sharp edges

Answer 1

Because...the chain has a larger area and hence the pressure exerted by the heavy tank on the ground decreases and prevent the tank sinking into ground.

Trucks and motorbus have wider tyres with respect to the property that "more the area & less the pressure is".So there will be less need for applying more pressure to handle the vehicle.And the vehicle will move smoothly.

The cutting edge of tools like knifes,blades,etc.,are provided with sharp edges to cut the things easily as the sharp edges have small area on which the force is applied,hence the more pressure is applied.

In short these all three cases are depend on pressure and area.

In case one more the area will less the pressure is.

In case two more the wider are is less the pressure will.

In case three less the area is more the pressure will.