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Notes- Sinking & Floating. Chapter 3, Lesson 3. Sink or Float?. Whether an object sinks or floats depends on the relative size of the buoyant force on the object and the weight of the object. If the buoyant force on an object is less than the object’s weight
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Notes- Sinking & Floating Chapter 3, Lesson 3
Sink or Float? • Whether an object sinks or floats depends on the relative size of the buoyant force on the object and the weight of the object.
If the buoyant force on an object is less than the object’s weight The net force on the object is downward The object will sink. (like the metal block) Sink or Float?
When an object is floating, it is not moving vertically The upward (or buoyant) force and the downward force (weight) are the same and cancel. (like the boat) Sink or Float?
The Buoyant Force & Density • An object will float if it is less dense than the fluid around it.
Metal boats float because they contain air, which makes their total density less than the water around them. The boat and block have the same weight, but the boat has more bouyant force. The Buoyant Force & Density
A hydrometer is an instrument that measures the density of a fluid. In a less dense fluid, it displaces more fluid and floats lower. In a denser fluid, it displaces less fluid and floats higher. The Buoyant Force and Density
Floating & Sinking in the Atmosphere • Like any fluid, air exerts pressure on things around it. • If the buoyant force due to air pressure on an object is large enough, the object can float in air.
Helium gas is less dense than air (nitrogen & oxygen) When a balloon is filled with helium, it is less dense than the air around it, and therefore floats. Floating & Sinking in the Atmosphere
Floating & Sinking in the Atmosphere • Whether a hot-air balloon rises or falls can be controlled by changing the density of the air inside the balloon. • Warm air has particles that are farther apart and therefore, it is less dense. (balloon rises) • Cool air has particles that are closer together and therefore, it is more dense. (balloon sinks)
Why does an object sink in water? A The object is denser than water. B The buoyant force is greater than the object’s weight. C The buoyant force is greater than the object’s mass. D The object is less dense than water.
Why does a hot-air balloon float? A The surrounding air is denser than the balloon. B The surrounding air is less dense than the balloon. C The balloon is denser than the surrounding air. D The balloon has less mass than the surrounding air.
What does a hydrometer measure? A mass of a solid B density of a solid C mass of a liquid D density of a liquid