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What Are Phenomena?
The Next Generation Science Standards (NGSS) emphasize the practice of science rather than the learning of disciplinary facts alone, isolated from the context of the natural world. Phenomena, which enable this kind of science education, are often classified as two types: anchoring, which typically serve as foci for an entire unit, and investigative, which serve as foci for a single lesson or short instructional sequences. We can observe phenomena in the natural world and use the Disciplinary Core Ideas (DCIs) of the physical, life and earth sciences to provide explanation. In NGSS, the seven Crosscutting Concepts (CCCs), such as Patterns and Energy and Matter, are shared across the different disciplines and are also used to explain phenomena. The application and unpacking of the DCIs and CCCs requires the use of one or more of the eight Science and Engineering Practices (SEPs), which include Planning and Carrying out Investigations and Analyzing and Interpreting Data. The “Thinking Like Scientists” example detailing Rutherford and Chadwick’s investigation is an example of NGSS in action. Rutherford began with an observation of a phenomenon (scattering of alpha particles by gold foil) and, working with a DCI in mind (matter was made up of atoms), questioned the nuclear composition of the atom. He determined through experimentation and data analysis (SEPs) that there must indeed be a small, dense nucleus. He further questioned the ability of the nucleus to maintain stability if only protons were present. From there, James Chadwick conducted a series of investigations with a new DCI in mind (the existence of a stable nucleus) and determined that a heavy, uncharged neutron was present in the nucleus and responsible for nuclear stability. Present throughout this entire process were the CCCs Cause and Effect and Energy and Matter.
Thinking Like Scientists: Studying Phenomena at University of Cambridge’s Cavendish Laboratory
The NGSS provide a framework in which students are meant to think like scientists. To help conceptualize this idea, imagine being present in the University of Cambridge’s Cavendish Laboratory during the early part of the 20th century when Ernest Rutherford and James Chadwick were investigating the nuclear constitution of the atom. At this time, scientists agreed that matter was made up of atoms. Rutherford knew there was more to learn about the atom and directed two of his students, Hans Geiger and James Marsden, to bombard gold foil with alpha particles, expecting that they would observe high-angle scattering (i.e., alpha particles that bounced off the gold foil as opposed to passing directly through it). Geiger and Marsden did indeed observe small amounts of such scattering, which led Rutherford to hypothesize that most of the mass of the atom was contained in a small, dense nucleus that held protons. This hypothesis led Rutherford to question why the nucleus did not break apart because of the repulsive interactions between protons.
With this in mind, James Chadwick bombarded beryllium atoms with alpha particles to study the radiation emitted by the beryllium as a result. When that radiation interacted with paraffin wax, it dislodged protons from the paraffin and the protons subsequently moved at a high velocity. At the time, scientists thought that the radiation emitted by the beryllium atoms must be high-energy photons, but Chadwick felt that this could not be the case because photons had no mass and could not be expected to knock anything loose from a target. As a result, he believed the emitted species was something relatively heavy and uncharged. He called this particle a neutron, owing to its ability to penetrate deep into a target without being repelled by positive protons or negative electrons.