What will happen if the motor car having petrol engine is refueled with diesel by mistake?

Why does one unconsciously speak louder than normal when wearing headphones?

ls it possible to ascertain directions from wrist watch like one does from compass?

How do sound waves travel through air? Why do they move faster in water than in air?

How millions of transistors switch-on and switch-off to register the digital 1 and 0 in the microchip?

Why the capacity of air-conditioners is expressed in tonnes, instead of horsepower?

How will the Universe end? Or will it go on expanding forever?

Why a multi-stage rocket is needed to get a spacecraft off the Earth and into the space?

How does a combination lock work? Why is it considered more secure than the cylinder lock?

From the viewpoint of economy, can hydrogen ever become a significant source of energy like petrol and diesel?