Frey Scientific's Harbottle lets you discover air pressure like never before. With just a balloon and a bottle, it has the ""WOW"" factor you have been searching for! Simply place the balloon into the opening of the bottle and stretch the mouth of the balloon over the mouth of the bottle. Blow into the balloon and, when it is fully inflated, close the bottom hole of the bottle with a stopper. The normal air pressure from outside allows the balloon to stay inflated! No twisting or tying required. Astonish your students even more with the strength of air pressure by filling the balloon with water before releasing the stopper! Excellent teaching tool for introducing pressure and discussing its applications, such as vacuum cleaners, flight, pumps, weather, and even how we breathe. Includes glass bottle, two balloons, rubber stopper, and Teacher's Guide with background information and activity suggestions for your students. Measures 5 inches diameter. Grades 5 and Above.