1 Bell Ringer What word should we think of when we think of pressure? 2. What is the formula for pressure? 3. What SI unit measures pressure? 4. What tool do we use to measure pressure?

2 Chapter 11.2 Floating and Sinking

3 Buoyancy Buoyancy is the ability to float. Buoyancy is the ability to float. The buoyant force is an upward force that acts on a submerged object. The buoyant force is an upward force that acts on a submerged object. A buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter. A buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter.

4 Buoyant force Since the pressure in a fluid increases with depth, the upward pressure on the bottom of the object is greater than the downward pressure on the top……this upward force is the buoyant force. Since the pressure in a fluid increases with depth, the upward pressure on the bottom of the object is greater than the downward pressure on the top……this upward force is the buoyant force.

5 The weight of an object under water is a downward force. The weight of an object under water is a downward force. The buoyant force is an upward force. The buoyant force is an upward force. If these are equal, the object stays where it is. If these are equal, the object stays where it is.

6 Archimedes’ principle Archimedes’ Principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces. Archimedes’ Principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

7 Why does a ship float?? The buoyant force will increase if more fluid is displaced. A large object displaces more fluid than a small object. The buoyant force will increase if more fluid is displaced. A large object displaces more fluid than a small object. Therefore, a greater buoyant force acts on the larger object, even if the objects weigh the same. Therefore, a greater buoyant force acts on the larger object, even if the objects weigh the same.

8 Density The density of a substance is its mass per unit volume. The density of a substance is its mass per unit volume. Density = mass Density = mass volume volume By comparing densities, you can predict whether an object will float or sink in a fluid. By comparing densities, you can predict whether an object will float or sink in a fluid.

9 SI Units Mass- grams Mass- grams Volume- cubic centimeters (cm 3 ) Volume- cubic centimeters (cm 3 ) Density units- g/cm 3 Density units- g/cm 3 If you are looking at the density of a liquid, the unit would be g/mL. If you are looking at the density of a liquid, the unit would be g/mL.

10 If an object is more dense than the fluid it’s immersed in, it will sink. If an object is more dense than the fluid it’s immersed in, it will sink. If an object is less dense than the fluid it’s immersed in, it will float. If an object is less dense than the fluid it’s immersed in, it will float.

11 Oil and Water

12 Changing density You can change the density of water by freezing it. You can change the density of water by freezing it. You can change the density of the object. Rather than using oxygen to fill a balloon, you can use Helium. Because it is less dense, the balloon floats in the air.. You can change the density of the object. Rather than using oxygen to fill a balloon, you can use Helium. Because it is less dense, the balloon floats in the air..

13 Bone Density Test