To illustrate that a body impelled horizontally will fall vertically at the same rate as a similar body allowed to fall freely. Comprises spring loaded L Section launcher with holes tor locating two 19mm dia steel ball which act as projectiles. Launcher is released by push button and projects one ball forwarded and allowing the other to fall freely. Mounted on wooden block, 180x60x30 mm which may be clamped to bench and has convenient storage pocket for the balls. Complete with 2 steel balls.