Fill a large fish tank or clear plastic tub with water.
Gather many different items for a sink/float experiment. Items might include a variety of bottles and containers in different sizes and shapes, a toy boat or rubber duck, a pencil or pen, metal paper clips or bottle tops, feathers, sponges and rocks.
Create a T-chart on an erasable whiteboard or poster board. Label one side "Float" and the other "Sink." Include a "Prediction" column if desired.
Gather students on the floor in front of the empty tub of water. Introduce the activity by asking, "What does it mean when something floats? What is the opposite of floating? Can you think of something that floats or sinks when you place it in water? Today we are going to perform an experiment with sinking and floating."
Point to the gathered items, telling students that the experiment involves placing each item into the water to see if it floats or sinks. Hold up each item individually, asking students to identify it. If desired, ask students to predict if it will float or sink when placed in the water.
Place each item into the tub one at a time. Give each student a turn at placing one item into the tank, if desired. After determining if the item sinks or floats, record the result in the appropriate column on the T-chart.
Give children a blank piece of paper to draw the experiment and its results.