Balloon in a syringe prank

Challenge your friend to inflate a balloon inside a syringe!

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.


  • sy­ringe;
  • bal­loon.

Step-by-step in­struc­tions

Place a bare­ly-in­flat­ed bal­loon in­side a sy­ringe. If you sim­ply move the plunger, noth­ing hap­pens. Plug the noz­zle of the sy­ringe with your fin­ger and be­gin to pull the pis­ton – the bal­loon in­flates!

Process de­scrip­tion

By cov­er­ing the sy­ringe’s noz­zle, you cre­ate a closed sys­tem with a fixed amount of air in­side. When you pull out the plunger, you in­crease the sy­ringe’s in­ter­nal vol­ume, which leads to a de­crease in pres­sure in the sy­ringe and on the sur­face of the bal­loon. The pres­sure in­side the bal­loon is equal to at­mo­spher­ic pres­sure, so the bal­loon in­flates un­til the in­crease in vol­ume and elas­tic force com­pen­sate for the pres­sure dif­fer­ence.

Im­press your friends with cool ex­per­i­ments from the MEL Physics sub­scrip­tion!