Student Exploration: Archimedes’ Principle
Vocabulary: Archimedes’ principle, buoyant force, density, displace, mass, volume, weight
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Why does a small pebble sink in water?.
A motorboat is a lot heavier than a pebble. Why does the boat float?
When you place an object in liquid, the downward pull of gravity causes it to start to sink. As the object sinks, the liquid pushes back up on the object with a force that opposes gravity.
In the Archimedes’ Principle Gizmo, you will see how these forces cause objects to either sink or float.
Check that the Width, Length, and Height of the boat are set to 5.0 cm. Drag one of the green 50-g cubes into the rectangular “boat.”
Add cubes until the boat sinks. What mass of cubes causes the boat to sink?
(Note: In this Gizmo, the mass of the boat itself is insignificant.)
Click Reset. Experiment with different boat dimensions until you create a boat that holds the most cubes without sinking.
What are the boat’s dimensions? Width: Length: Height:
How much mass can the boat hold without sinking?
Get the Gizmo ready:
Set the Width, Length, and Height to 5.0 cm.
Be sure the Liquid density is set to 1.0 g/mL.
Question: How does the mass of the boat relate to the amount of displaced liquid?
Observe: Place several of the 50-g cubes into the boat. What happens to some of the liquid in the tank?
The liquid that is pushed into the graduated cylinder is called displaced liquid.
Predict: How do you think the mass of the boat will relate to theamount of displaced liquid?
Observe: Click Reset. Drag two cubes into the boat, yielding a total mass of 100 grams. How much water is displaced into the graduated cylinder? (Units are mL.)
Experiment: Click Reset. Choose a new set of boat dimensions. Add cubes to the boat and record the volume of displaced liquid. (If the boat sinks, try a larger set of dimensions.) Record your findings for three boats in the table (include units). Leave the last column blank.
Calculate: Density is equal to mass per unit volume. To calculate density, divide an object’s mass by its volume.
If the liquid’s density is 1 gram per milliliter (the density of water), the mass in grams is equal to the volume in milliliters. Use this information to fill in the last column of your data table.
Draw conclusions: What is the relationship between the mass of the boat and the mass of the displaced liquid?