Chapter 11 Section 2: Floating and sinking Key concepts: what is the effect of the buoyant force? How can you use density to determine whether an object will float or sink in a fluid? Key terms: buoyant force, Archimedes’ principle, density

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Buoyancy Buoyancy – ability to float Buoyant force – upward force that water and other fluids exert – Acts in a direction opposite to the force of gravity, so it makes an object feel lighter Fluid exerts pressure on all surfaces of a submerged object Since pressure in a fluid increases with depth, the upward pressure on the bottom of the object is greater than the downward pressure on top. This is the buoyant force

Buoyant force Weight of a submerged object is a downward force If an object’s weight is greater than the buoyant force, a net force acts downward on the object and the object will sink. If weight is equal to the buoyant force, it floats.

Archimedes’ principle Archimedes – mathematician in ancient Greece His principle states that the buoyant force acting on a submerged object is equal to the weight of fluid the object displaces (this is why stuff floats – like ships – look at figure 10 page 383) A large object displaces more fluid than a small object.

Density Why do some things float and others sink? Density: mass per unit volume (d= m/v) By comparing densities, you can predict whether an object will float or sink in a fluid. The density of water is 1.00 g/cm 3 If something has a greater density, so greater than 1, it will sink in water (look at figure 11, pg 383). If it has a smaller density, like wood, it will float.

Changing Density Changing density can explain why an object floats or sinks. For example, ice is less dense than water. Why? When water freezes, the ice expands, so it occupies more space (takes up more volume). You can make an object sink or float in a fluid by changing its density.

This is everything you will need to know for the chapter quiz next week Your quiz will be Wednesday Start reviewing – get a good grade – improve your grade – smile all the way home – feel fantastic about yourself -