Knowledge and Skills Statement
Matter and energy. The student knows that matter has measurable physical properties that determine how matter is identified, classified, changed, and used.
Further Explanation
In everyday use, mass and weight are sometimes incorrectly used interchangeably. Students in grade 4 are expected to measure mass, however they are not expected to understand the role gravity plays in differentiating between mass and weight. In science, mass is always measured in metric units (kilograms). Experiences in science with scales and balances will help support students' development of understanding mass versus weight, while in mathematics students will understand units of measurement as customary and metric.
As an educator, it is important to understand the differences between mass and weight. Weight is measured on a scale and accounts for the downward force of gravity. When measuring mass, an object is placed on one side of a balance and counterweights are placed on the opposite side of the balance. This use of a counterbalance means that the measurement taken is consistent regardless of the force of gravity in an environment. In other words, while the weight of an object measured on a scale is lighter on the Moon than it is on Earth, the mass of the object measured with a balance would be the same in both locations.
When investigating density, students should have direct experiences with various substances and tools to measure their properties, such as Celsius thermometers, digital scales and/or balances, magnets, beakers, and graduated cylinders. Students should observe solids and liquids that float in water (for example, vegetable oil, pumice stone, apple, ice) and substances that sink in water (for example, glass marble, grape, glycerin, corn syrup). The ability of an object to float in water depends on the amount of water displaced by the object. If the object weighs more than the amount of water it displaces, the object will sink. If the object weight less than the amount of water it displaces, the object will float. This is called buoyancy and explains how a steel cargo ship can float on the ocean. Buoyancy is related to, but different from the density of an object. Density is the amount of mass in a specific amount of space or volume. A denser object will be heavier than a less dense object of the same size. A denser object will need to displace more water in order to float.
Supporting Information
Research
Vincent, Dan, Darlinda Cassel, and Jeanie Milligan. “Will It Float?” Science and Children 45, no. 6 (February 2008): 36–39. https://www.proquest.com/docview/236960208?pq-origsite=gscholar&fromopenview=true&sourcetype=Scholarly%20Journals.
Summary: This experiment was inspired by upper-elementary students’ response to a previous activity where they found that sometimes larger objects can weigh less than smaller objects. This lesson is based on the 5E model and is used to help students explore mass, density, and volume. Students predicted whether different items would sink or float and were confused by why some types of wood and rocks would float while many others would sink. Students also predicted the mass of objects of different sizes and recorded their observations. Students tested whether objects made of plastic and aluminum would float and measured their volume and mass along with measuring the mass of the water. They then graphed this data use different colors and used it to explain the relation between mass, volume, and density. Teachers evaluated student understanding throughout the activity by observing conversations among students and asking questions.