Vacuum cannon, illustration. This device uses atmospheric pressure to accelerate projectiles to supersonic speeds. The projectile is placed at the head of a long cylindrical tube, which is sealed at both ends and the air inside is then evacuated using a vacuum pump (far left). When the seal at left is broken, the pressure of the air forces the projectile (here, a table tennis ball) along the tube at supersonic speeds. The projectile is seen smashing through a target (red) at far right.