a drinking straw a glass jar by adhesive tape a balloon a pair of scissors a vertical surface cut the straw to give it a pointed shape you stretch the balloon over the mouth of the jar cut a piece of by adhesive tape and stick it at the center of the balloon now stick the flat side of the straw to the sticky tape bring the vertical surface near to the pointed part of the straw the barometer is ready with a pencil mark the position of the tip of the straw on the vertical surface repeat this every day for one week can you notice any difference in the inclination of the straw let us see why if the atmospheric pressure rises it becomes greater than the pressure within the jaw when it was closed as a consequence the air in the jaw gets compressed the balloon drops lower and the straw moves upward when atmospheric pressure decreases instead the pressure within the jaw is greater and the balloon membrane Rises as a consequence the straw drops when out mysteric pressure drops probably bad weather is on its way on the contrary if there is high atmospheric pressure it means that the weather is good