These proceedings contain the papers of the 18th International Conference on Cognition and Exploratory Learning in the Digital Age (CELDA 2021), held virtually, due to an exceptional situation caused by the COVID-19 pandemic, from October 13-15, 2021, and organized by the International Association for Development of the Information Society…

Discusses simple interval timers for microcomputers, including (1) the Jiffy clock; (2) CPU count timers; (3) screen count timers; (4) light pen timers; and (5) chip timers. Also examines some of the general characteristics of all types of timers. (JN)

Describes the theory and application of an atomic fountain which pushes the atoms by laser pulses. Discusses the applications in measuring atomic properties and in building an atomic clock. (YP)

Lists directions for creating some laboratory equipment that makes it easier for students to assess the rate at which an enzyme is modifying its target (substrate). (WRM)

Describes the construction of a conductivity meter that includes a timer and a readout display that provides semiquantitative information. The meter can be made into a hand-held or lecture hall (demonstration) version. (WRM)

Describes a recently discovered and translated work by Archimedes in which he constructed a balance to determine the amount of gold in an alloy of gold and silver. A description of the balance (translated verbatim) as found in Archimedes' work "On Balances" is included. (JN)

A simple apparatus (constructed of glass) for measuring surface tension is described. Procedures and typical results are included. (JN)

Instructions for making a simple respirometer, to measure rates of oxygen consumption of organisms, are presented. The instrument incorporates most of the basic elements of commercial respirometers but can be made inexpensively by high school students. Operating instructions and applications are given. (Author/SA)

Describes an inexpensive device (around $8.00) for measuring light. The circuit used includes five resistors, three small capacitors, a cadmium sulfide light sensor, two integrated circuits, and two light-emitting diodes. The unit is constructed on a small perforated circuit board and powered by a 9-V transistor radio battery. (JN)

Macrolab (located at New Jersey Institute of Technology) develops devices, training models, and experiments for the scientific education of handicapped students. The construction and operation of a spectrophotometer for blind and visually impaired students are discussed. Construction details are available from authors. (JN)

Described is a LOGO computer program that enables students to investigate the relationship between a digital number and the resistance in a variable resistor used to generate that number. Likewise, actual temperature readings and the corresponding resistance within a thermistor can be used for data gathering and subsequent analysis. (JJK)

Described are several activities to be used to help students grasp the concept of floating. The activities include the use of a spring scale to measure the weight of the objects in air, in water, and in salt water, and a discussion of why there are differences in these weights. (DS)

The heat content of a food at a given temperature can be described by the thermodynamic property of enthalpy. Presents a method to construct a simple calorimeter for measuring the enthalpy changes of different foods during freezing. (MDH)

The Zimbabwe Secondary School Science Project (ZIM-SCI) developed student study guides, corresponding teaching guides, and science kits for a low-cost science course which could be taught during the first 2 years of secondary school without the aid of qualified teachers and conventional laboratories. This ZIM-SCI study guide presents activities…

Outlines procedures for constructing an instrument which uses an electrode and calibration methods to measure the salinity of waters in environments close to and affected by a saline estuary. (Author/DC)