Question

What is common in the working of the devices such as drinking straw, a dropper and a

rubber ?

Answer 1

I am not quite sure about the rubber but the answer I hope is :

They all work on the principle of Pressure Difference. The objects would from high pressure region to low pressure. As in the straw, a low pressure (lower than the atmospheric pressure) will be created on the upper area, thereby the atmosphere would force the liquid in through the straw. For the dropper one applies pressure on the top part, thereby forcing the liquid out through the other end.

Hope you understand.

Answer 2

All the devices like drinking straw , syringe , a dropper and a rubber suck uses the atmospheric pressure to work.