Ever wonder how a small life jacket can keep your larger body afloat? An object displaces water, which pushes back and causes buoyancy (the more water you displace, the greater the force that pushes back). A life jacket is filled with a very light material, so it can displace a lot of water compared to its weight, meaning it will float high on top of the water and keep your head above the surface. Next time you take a rafting trip, think about the physics involved: learn about how things float, the force and torque from the water and paddle, and the logistics of crossing running water. Most guides can also give you interesting facts about the river in which you are rafting, its history, and its surrounding wilderness. Don’t stop asking questions!
BEFORE YOU GO
- Explore students’ prior knowledge about kayaking and rafting. How many students have kayaked or rafted? What do they know about how to do these activities?
- Review relevant vocabulary and key terms: current, float, density, gravity, mass, force, torque.
- Call ahead to the kayak/raft company and inquire about maps and information about the river or waterway the students will be exploring, as well as the vessels they’ll be using.
- Perform a preliminary experiment with the students involving floating and sinking. Ask them to ponder why bath toys float in the bathtub but soap sinks. Also have them consider what would happen to a full bottle of shampoo in a bathtub and what would happen to the same bottle as shampoo is removed from it. Allow them to experiment with bottles of varying fullness and make hypotheses about why some are floating and some are sinking.
Students learn about the science and physics behind kayaking and rafting.
WHAT TO WONDER
Ask: Why does this kayak/raft float? How will its ability to float change when I get into the vessel?
Describe the shape of the boat and its paddles, the movement of the water.
Observe what happens to the boats and the surrounding water when people get in and out of them and what the water looks like while someone is paddling?
Opinion: Do you prefer paddling with others? With a current? Against a current? Why?
Compare objects you saw float and objects you saw sink. Explain.
Challenge: Explain what a kayaker/rafter must do to stay still in moving water.
Discuss the science/physics vocabulary and key terms and how they apply to your experience on the water.
Project: Create a vessel that floats.
Research why the Titanic sank?
Social Impact: In response to the 1.2 million people who drown around the world and the thousands of boaters who die or are injured every year, create a public service announcement/poster explaining/reminding swimmers and boaters why some things float and some things sink. Or research and get involved in one of the many organizations that sponsor kayaking events to raise money for charity: