Carla makes a small cardboard boat and floats it in a tub of water. When she adds a drop of dish soap behind the boat, the boat moves forward.Which statement best explains what happened?
Answer
A
The soap increased the viscosity of the water behind the boat, allowing the water in front of the boat to flow more easily.
B
The soap reduced the surface tension behind the boat, causing both water molecules and the boat to be pulled forward.
C
The soap increased the kinetic energy of the water molecules behind the boat, causing both the molecules and the boat to move forward.
D
The soap formed an immiscible layer on the water, causing the soap to spread out and push the boat forward.
Explanation
Dish soap lowers the water’s surface tension where the drop lands, behind the boat. The water in front has greater surface tension, so the imbalance pulls the boat toward the higher-tension water and makes it move forward. The soap does not need to increase the water’s viscosity or form a separate immiscible layer.
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