Density. Density is how concentrated or compact matter is.

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1 Density Density is how concentrated or compact matter is. Packing snow into snowballs increases its density. You are squeezing large amounts of matter into small volumes of space.

2 Equation for Density = m V density= mass volume

3 Changing the Density You can make an object denser without adding any any mass (or weight) by squeezing it into a smaller space. When the volume of a loaf of bread is reduced, its density increases.

4 Density of Water A liter of water occupies a volume of 1000 cm 3 and has a mass of 1 kg. Its density is 1 kg/l. No matter how much water you have, its density is the same.

5 Float or Sink? Any substance that is less dense than water will float in water. If the substance's density is greater than water's density, then it will sink. The density of ice is 0.92 g/cm 3. The density of liquid water is 1.0 g/cm 3. Therefore, ice should float in water.

6 Pressure P= F A pressure= force area

7 Although the weight of both books is the same, the upright book exerts a greater pressure against the surface of the table. Pressure

8 Pressure in a Liquid Liquid pressure = weight density x depth The deeper you go underwater, the greater the pressure. Why is this water tower so high above the ground?

9 Pressure in a Liquid Having a great depth of water above the ground helps insure that reliable water pressure is supplied to the many homes it serves. depth

10 Pressure Behind a Dam The average water pressure acting against the dam depends on the average depth of the water and not on the volume of water held back. Which dam must be built stronger?

11 Buoyancy in a Liquid The greater pressure against the bottom of the submerged rock produces an upward buoyant force. Even objects that are dense enough to sink will have a buoyant force exerted on them when underwater.

12 Archimedes' Principle An immersed body is buoyed up by a force equal to the weight of the fluid it displaces. When a stone is submerged, it displaces a volume of water equal to the volume of the stone. Will the buoyant force on the stone be enough to keep it from sinking?

13 Archimedes' Principle Yes, if the object is less dense than water. A floating object displaces a weight of fluid equal to its own weight. Why does some of the block of wood stick up above the water's surface?

14 Archimedes' Principle For objects that sink, the buoyant force on them is not great enough to support their entire weight.

15 Why Do Ships Float? Iron is nearly 8 times denser than water. A solid bar of iron sinks straight to the bottom of any container of water. So why do ships that are made of iron float?

16 Why Do Ships Float? The trick is to get the iron to displace more water by shaping it like a bowl.

17 Flotation Additional weight or cargo requires that additional water be displaced. This results in a larger buoyant force that is needed to support that extra weight!

18 The Lava Lamp Wax at the bottom is heated by the lamp, expands, becomes less dense and floats to the top. Wax at the top now cools down, contracts, becomes more dense, and sinks. heat source

19 Pressure in a Gas The overall effect of millions of gas molecules colliding with each other is what we call pressure. When you pump more air into a tire, you increase the density, making collisions between molecules more likely. This increases the pressure.

20 Because the flow is continuous, water must speed up when it flows through the narrow part of the brook. Fluid Flow

21 Bernoulli's Principle Where the speed of a fluid increases, internal pressure in the fluid decreases. slower faster more pressure less pressure Water speeds up when it flows into the narrower part of the pipe. The bubbles are bigger in the narrower part because internal pressure there is less.

22 Bernoulli's Principle Air must flow faster over the top of the airplane wing. According to Bernoulli, the pressure there must become less. A lifting force is generated that tries to push the wing up toward the area of lower pressure. lift drag