Introduction:
Those who have swam in the ocean water can related to the difference in fresh and salt water. Children visit the beach often and will relate to the difference of the water in a pool and beach water. Besides the difference in taste we will explore the buoyancy force of salt water, which allows things to float with greater ease than is possible in fresh or pool water. Children will also learn that ships also are known to ride higher in salt water than in fresh water. The buoyant force of salt water can be demonstrated in the classroom using tap water to which table salt has been added.
Learning Objectives:
As a result of the demonstration lesson, students should * Understand the concept of density. * Develop an awareness of relative density as it relates to an object and the water in which it is placed. * Relate the demonstration to other situations that illustrate relative density like ships at sea. * Explain the floating and/or sinking of an object in water in terms of key works: density, buoyancy, and relative density.
Materials Required: 1. 2 drinking glasses 2. tap water 3. table salt 4. 2 fresh eggs
Presentation:
1. Obtain two identical drinking glasses and distinguish them by marking: S for saltwater and F for fresh water. 2. Pour tap water into the glasses until each is two-thirds full. 3. Add two tablespoons of table salt to the water in “S” and allow it to dissolve completely. 4. Gently lower a fresh egg into each of the glasses 5. Observe what happens to the egg placed in each type of water.
Rational:
The buoyant force of water is determined by the density of the water and the object placed in it. An object that is less dense than water will float; an object that is more dense will sink. Only by
