Sain wedi'i Rhannu

Kya aapne kabhi socha hai ki 1930 mein bina kisi modern crane ya concrete mixer ke bade-bade ghar kaise bante the? ​05-15s: Us zamane mein sabse zyada use hone wali machine thi—"The Hand-Crank Concrete Mixer." Aaj ke diesel engine ki jagah, ise hath se ghuma kar cement mix kiya jata tha. ​15-30s: Bhari pattharon aur beam ko upar pahunchane ke liye "Block and Tackle" (pulleys ka system) aur "Derrick Cranes" ka istemal hota tha, jo puri tarah se manual gear par chalti thi. ​30-45s: Deewaron ki