Exam Review Mass, Weight, Density, Buoyancy, States of Matter

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1 Exam Review Mass, Weight, Density, Buoyancy, States of Matter Volume An object s volume is the amount of space it takes up. The volume of a cup of water can change if you freeze it in to a solid or boil it in to a gas but there will still be the same number of water particles. Find the volume of a regular object by measuring it. For a cube, just multiply LxWxH. Measured in ml, l (litres), cm 3, etc. Find the volume of an irregular object using displacement. Place the object in an overflow container and measure the amount of water that is displaced or pushed out of the way using a graduated cylinder. Density The relationship between mass and volume Something that is very dense, has a large mass relative to its volume. Something that is not very dense, has a small mass relative to its volume. D = M Calculated by dividing its mass by its volume. V How tightly atoms are packed together. Density Rule If an object is less dense than the liquid in which it is immersed (put in), it will float, if it is denser it will sink, and if its density is equal, it will hover. Average Density Ships can be built of steel (density = 9.0 g/ml) as long as they have large, hollow hulls. Even very dense materials can float if they can be shaped in a way to increase their volumes. Fish and submarines adjust their average densities to allow themselves to float, sink, and hover. Mass The amount of matter (stuff) in an object regardless of the amount of space it takes up or the forces acting on it. Mass does not change when you go to the moon or to a different planet. Measured in mg, g, kg, etc. Weight The force of gravity being exerted on the mass of an object. You d be much lighter on the moon because there is much less gravity. You d be much heavier on Jupiter because there is much more gravity. Measured in Newtons (N).

2 Buoyancy How something behaves in water Positive Buoyancy An object with a density less than 1 g/ml (in water) An object with a density less than the liquid in which it is immersed Negative Buoyancy An object with a density greater than the liquid in which it is immersed An object with a density greater than 1 g/ml (in water) Neutral Buoyancy An object with a density equal to the liquid in which it is immersed An object with a density equal to 1 g/ml (in water) Changing Buoyancy A submarine changes its density and therefore its buoyancy by changing its MASS. A submarine changes its density by filling and emptying the ballast tanks. The volume of the sub does not change (can t add any space to the sub), but the addition of water changes the mass (water makes it heavier). Ballast Tanks - Submarines have two strong hulls to protect them from collapsing under the extreme pressure they encounter at sea. Between these two hulls are a series of ballast tanks that can be filled with a mixture of water and air. When a submarine submerges, it fills its ballast tanks with seawater until its overall density is greater than the water around it. To return to the surface, the crew forces the water out of the tanks with compressed air, which is much less dense, allowing the submarine to float. Subs control their buoyancy by adjusting their mass. A fish changes its density and therefore its buoyancy by changing its VOLUME. A fish changes its density by filling and emptying its swim bladder. The mass of the fish does not change (there isn t any more or less fish), but the addition of air changes the volume (the size of the fish gets larger or smaller). Swim Bladder - an air-filled sac near the centre of the body. A fish can change its volume without significantly changing its mass. When the swim bladder contracts, the air inside it is compressed into a smaller volume and the fish becomes more dense, causing it to sink. By expanding the swim bladder and increasing its volume, the fish becomes less dense than water, and begins to rise.

3 Tools Triple Beam Balance Used to measure the mass of objects Graduated Cylinder & Overflow Can The volume of water displace is equal to the volume of the object. Solid The state of matter of a substance that has a definite shape and volume. Made up of particles that are tightly packed together, like bees in a hive. The particles of a solid are so close together that they cannot move around freely they can only vibrate. Sugar, salt, flour, powdered cleansers and detergents, and many other crystals and powders that we use every day are examples of solids that can be poured. Each tiny fragment of these solids contains billions of even smaller particles that are tightly packed together. Each tiny fragment is like a miniature solid in itself. This explains why solids form a pile when they are poured and why they do not keep flowing apart from each other. Liquid The state of matter of a substance that has a definite volume, but no definite shape. The particles that make up liquids have enough energy to pull away from each other and slide around each other, while at the same time vibrating close together in small clusters.

4 Another way to think about what is happening on the level of the particles is to imagine groups of guests talking and dancing at a party. The party guests can move around by shifting as a group, or by flowing in between the other groups of partygoers. Similarly, liquid particles can slip past each other. Unlike the particles in solids, they do not form rigid clumps. As a result, the particles of a liquid cannot hold their shape; instead, they fill a container and take the shape of that container. Liquids always flow to the lowest possible level, like the water flowing over a waterfall. Gas The state of matter of a substance that has neither a definite shape nor a definite volume. Gas particles are so free to move that they do so in every direction, and they have a great deal of energy to move extremely far apart. Therefore, gas particles spread out so much that in a brief time, they fill up the space of an entire container or room. For this reason, gases, like liquids, take on the shape of the container in which they are sealed. For example, water vapour forms clouds that float in the sky. Unlike what happens to liquids, when the lid is taken off a container of gas, the gas particles will start to spread apart again, until they have filled the entire room or building. Changes in Temperature: When a solid is heated, the particles gain more energy and vibrate faster. As more heat is added, this speed of vibration becomes so fast that the force of attraction cannot hold the particles together. The rigid structure of the solid falls apart, melting occurs, and a liquid is formed. In a liquid, the particles are slightly less tightly packed together (less dense) than in a solid. As more heat is added to a liquid, the particles move even faster. The forces of attraction between them are broken, and the particles are able to move in all directions, leaving larger spaces in between. The particles take up more space or volume, making the density lower. Particles eventually escape from the liquid, and a gas is formed. The reverse process occurs when heat is taken away from a gas or a liquid as its temperature decreases.

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