Final answer:
A dropped test tube breaks upon impact with the classroom floor due to its brittleness and inability to absorb energy. The floor, being made of tougher material, does not show damage. The average force experienced upon impact determines the likelihood of breakage.
Step-by-step explanation:
If a test tube is dropped in class, it may break upon impact whereas the floor may show no damage because the test tube is made of a brittle material that lacks the ability to deform or absorb much energy upon impact. Glass, the material of the test tube, has a high elastic limit but low toughness, meaning it can withstand a certain amount of stress but once that limit is exceeded, it fails catastrophically by shattering. On the other hand, the floor is usually constructed of a much tougher material, like concrete or tile, designed to absorb and distribute the force of impacts without showing damage.
Whether or not an object breaks depends on the average force exerted on it upon impact. A 1.2-kg glass figure, for example, breaks when the force exceeds 330 N. If this figure hits a hard surface like a tile floor, it stops quickly, and the average force it experiences is high, leading to breakage. If the same figure were to fall onto a padded or carpeted surface, the time taken to come to a stop would be longer, resulting in a lower average force and a reduced chance of breakage. This indicates that the surface onto which an object falls greatly influences its likelihood of breaking.