The pendulum impact tester can be used to measure impact strength of films. An impacting head on the end of pendulum is swung through an arc into and through sample. Tester has a means of measuring difference between potential energy of pendulum at maximum height in free swing and potential energy of the pendulum after rupture of sample. This difference in energy is defind as impact strength and is reported in units of kilogram-centimeters. It is useful in predicting resistance of a material to breakage from dropping or other quick blows.
A test similar in scope, method and sognificance is the dart test for polyethylene film. Weighed dart is dropped from standard height onto taut sample. Significance and purpose are the same as in the pendulum test. Dart unit is weight of dart in grams that breaks sample 50 percent of the time.
These tests give an index of material's dynamic dtrength and approximate what will occur when package is dropped.