Question

why an empty bottle gets crushed when placed in open

Answer 1

because it hasn't any material inside and the pressure of heat crushes it

Answer 2

Empty bottle free of air gets crushed due to the atmospheric pressure. A bottle is never empty. It is always filled up with air which prevents the bottle from crushing. Sucking a juice from a glass occurs for the same reason which is caused due to atm. Pressure which is exerted on the juice when the juice is pumped up or sucked up by a straw. Atm. pressure is a important factor for mataining the balance of the environment.