Published on June 26, 2007
Metric System: Metric System Metric System: Metric System Developed by the French in the late 1700’s. Based on powers of ten, so it is very easy to use. Used by almost every country in the world, with the notable exception of the USA. Especially used by scientists. Abbreviated SI, which is French for Systeme International. Metric Prefixes: Metric Prefixes Regardless of the unit, the entire metric system uses the same prefixes. Common prefixes are: kilo = 1000 centi = 1/100th milli = 1/1000th 1 meter = 100 centimeters= 1000 millimeters Length: Length Length is the distance between two points. The SI base unit for length is the meter. We use rulers or meter sticks to find the length of objects. Mass: Mass Mass is the amount of matter that makes up an object. A golf ball and a ping pong ball are the same size, but the golf ball has a lot more matter in it. So the golf ball will have more mass. The SI unit for mass is the gram. A paper clip has a mass of about one gram. The mass of an object will not change unless we add or subtract matter from it. Measuring Mass: Measuring Mass We will use a balance scale to measure mass. Gravity pulls equally on both sides of a balance scale, so you will get the same mass no matter what planet you are on. Measuring Weight and Forces: Measuring Weight and Forces A force is a push or a pull. The SI unit for force is the Newton (N). Spring scales will be used to measure forces. Since weight is the force of gravity acting on objects, we will use the Newton for weight also. Weight: Weight Weight is a measure of the force of gravity on an object. Your weight can change depending on the force of gravity. The gravity will change depending on the planet you are on. The SI unit for weight is the Newton (N). The English unit for weight is the pound. Gravity: Gravity Gravity is the force of attraction between any two objects with mass. The force depends on two things: more distance = less gravity = less weight less distance = more gravity = more weight more mass = more gravity = more weight less mass = less gravity = less weight Weight and Mass: Weight and Mass Notice that Jill’s mass never changes. Her mother will not allow us to take parts off her, or add parts to her, so her mass stays the same. Jill is 30kg of little girl no matter where she goes! Slide11: Volume: Volume Volume is the amount of space contained in an object. We can find the volume of box shapes by the formula Volume = length x width x height In this case the units would be cubic centimeters (cm3). So a box 2 cm x 3 cm x 5cm would have a volume of 30 cm3 Base Units: Base Units The base unit for volume is the Liter. We measure volume with a graduated cylinder. Liquid Volume: Liquid Volume When the metric system was created, they decided that 1 cm3 of water would equal 1 milliliter of water and the 1 mL of water will have a mass of one gram. 1 cm3 of anything = 1 mL of anything 1 cm3 water = 1 mL of water = 1 gram Water Displacement: Water Displacement We can use water displacement to find the volume of objects that are not boxed shaped. We can put 50-mL of water in a graduated cylinder. If a rock causes the level to rise to 73-mL, the the rock must have a volume of 23-mL. Water Mass and Volume: Water Mass and Volume 1 cm3 water = 1 mL of water = 1 gram So what would be the mass of 50 mL of water be? 50 grams So what would be the mass of 1 liter of water be? 1 L = 1000 mL so its mass would be 1000 grams or a kilogram. Density: Density Density is the amount of matter (mass) compared to the amount of space (volume) the object occupies. We will measure mass in grams and volume in mL or cm3 Density Formula: Density Formula Density is mass divided by volume. Density = mass/volume Remember, all fractions are division problems. The top number always goes in the house! Since the unit for mass is grams, and the unit for volume is mL or cm3, then the unit for density is g/mL, or g/ cm3 Density Formula Wheel: Density Formula Wheel Formula wheels make it easy to solve density problems. Cover the property you are trying to find, and do what is left over. To find density, cover the word density. You have mass over volume remaining. So divide mass by volume to find density! Mass density volume Density Formula Wheel: Density Formula Wheel To find mass, you cover the word mass. You now have mass times volume remaining. To find volume, cover volume. You have mass over density remaining, so divide mass by density to find volume. Mass density volume Understanding Density: Understanding Density In the following illustrations, each will represent 1 cm3. Each g will represent 1 gram. Mass = 24g Volume = 8 cm3 Density = 3g/cm3 Slide22: In other words, there are 3 grams in every cm3. Density Problem 2: Density Problem 2 Mass = 12 grams Volume = 6 cm3 Density = 2 g/cm3 In English we say the density of the object is 2 grams in every cubic centimeter. Density Problem 3: Density Problem 3 Our previous problems were materials of uniform density. They were the same stuff throughout. But many materials are not. Gravel is a great example. Mass = 16 grams Volume = 8 mL Density = 2 g/mL Water and Density: Water and Density Since 1-gram of water has a volume of 1-mL, then the density of water will always be 1 gram/mL. 5o-mL of water will have a mass of 50 grams, so again the density of pure water will be 1 g/mL. A kg of water will have a volume of 1000-mL, so it’s density will be 1 gram/mL. Floating and Sinking: Floating and Sinking Less dense materials will float on top of more dense materials. Objects with a density of less than 1-g/mL will float on top of water. Objects with a density greater than 1 g/mL will sink in water. Neutral Buoyancy: Neutral Buoyancy Objects with a density equal to the density of water will float in mid water, at what ever level you place the object. Fish and submarines control their depth by changing their density. Objects that Sink!: Objects that Sink! Objects with a density greater than 1 g/mL will sink in water. Titanic Sails the Ocean Blue: Titanic Sails the Ocean Blue The Titanic is sailing on its maiden voyage. What is the density of this enormous, steel hulled ship, full of machinery, coal, people, and all sorts of heavy things? It’s floating, so it’s density must be less than 1 g/mL. How can this be? The Titanic is a hollow vessel full of air! Titanic verses Iceberg: Titanic verses Iceberg After HMS Titanic struck the iceberg, she started to fill with water. What happened to her density? As she took on more and more water, her density got closer and closer to 1 g/mL. The denser the ship became, the lower she settled into the water. Wreck of the Titanic: Wreck of the Titanic What is the density of the Titanic resting on the ocean floor? Must be greater than 1 g/mL, as her steel hull is full of water instead of air. Slide32: Specific Gravity: Specific Gravity Pure substances will always have a certain density. When we compare their density to that of water we call it specific gravity. This is one way we can identify materials. Density Review: Density Review We don’t actually count g’s to find the mass of objects. How would you find the mass of a rock? Use a balance scale. In real life how would you find the volume of a rock? Use a graduated cylinder and see how much water the rock displaces. Classification: Classification Grouping together objects that are alike in some way. You can classify by size, color, weight, shape, use, and many other important characteristics. This makes it easier to see the relationships between different objects.