KIDS TUTORIAL Worksheet/Information Sheet Worksheet/Information Sheet No: Student’s Name : Subject : Physics Date : Topic Teacher’s Name :Shahriar Turja Class : O Level : Floating and Sinking Density: The compactness and size of the molecules or particles of a substance the more compact or squished together the molecules are and the more mass the particles have, the larger the density Density is a characteristic property of substances and can be used to help identify substances. MASS: is the amount of matter an object contains Mass does not change unless you add or remove matter VOLUME: is the amount of space an object occupies Density = Mass / Volume Finding Mass and Volume • Mass is always determined using a balance. – • • Triple beam or electronic Remember you always must take into account the mass of the container one of two ways: – Tare the balance (zero out the container’s mass) – Or measuring the mass of the container and then subtracting it out later from the total mass of the container + substance Volume can be found in different ways, depending on the substance or object. • Liquid volumes are read in volumetric lab equipment, like a graduated cylinder or pipet. The dimensions of regularly shaped objects may be measured and then the volume found by using a formula such as V=l x w x h. • The volume of irregularly shaped objects may be found by water displacement • measure a given amount of water in a graduated cylinder • add the object and read the volume of the water + object • then find the volume of the object by subtraction. Amount of H2O with object = ______ About of H2O without object = ______ Difference = Volume = ______ Units • Mass units are usually grams (g) • Volume units are usually – Milliliters (mL) or cubic centimeters (cm3) for liquids or solids • – 1mL = 1cm3 L for gases Density units will always be a (Mass unit/ volume unit) like g/mL or g/cm3 or g/L. Using the density formula • D=m/v can be used to solve for density if the mass and volume is known • What if the density is known, and you need to find the mass or volume? – Just rearrange the formula to solve for the unknown: m=D*v or v=m/D Upthrust: When a body is partially or wholly immersed in a liquid, and upward force acts on it known as upthrust. Upthrust is a force, it is measured in Newton (N). The Effect of upthrust: Its effect is that weight of the body immersed is liquid appears to be less than its actual weight. Plimsoll line: The Plimsoll line is a reference mark located on a ship’s hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo. This depth varies with a ship’s dimensions, type of cargo, time of year, and the water densities encountered in port and at sea. Once these factors have been accounted for, a ship’s captain can determine the appropriate Plimsoll line needed for the voyage Hydrometer: A hydrometer is an instrument to measure the relative density of liquids. It consists of a tube with a bulb at one end. Lead shots are placed in the bulb to weigh it down and enable the hydrometer to float vertically in the liquid. In a liquid of lesser density, a greater volume of liquid must be displaced for the buoyant force to equal to the weight of the hydrometer so it sinks lower. Hydrometer floats higher in a liquid of higher density. Application of Archimedes’ Principle 1. Submarine: A submarine has a large ballast tank, which is used to control its position and depth from the surface of the sea. A submarine submerges by letting water into the ballast tank so that its weight becomes greater than the buoyant force. Conversely, it floats by reducing water in the ballast tank. -thus its weight is less than the upthrust (buoyant force). 2. Hot-air balloon The atmosphere is filled with air that exerts buoyant force on any object. A hot air balloon rises and floats due to the buoyant force (when the surrounding air is greater than its weight). It descends when the balloon’s weight is higher than the buoyant force. It becomes stationary when the weight equals the buoyant force. The weight of the Hot-air balloon can be controlled by varying the quantity of hot air in the balloon. 3. Ship A ship floats on the surface of the sea because the volume of water displaced by the ship is enough to have a weight equal to the weight of the ship. A ship is constructed in a way so that the shape is hollow, to make the overall density of the ship lesser than the sea water. Therefore, the buoyant force acting on the ship is large enough to support its weight. The density of sea water varies with location. The PLIMSOLL LINE marked on the body of the ship acts as a guideline to ensure that the ship is loaded within the safety limit. A ship submerge lower in fresh water as fresh water density is lesser than sea water. Ships will float higher in cold water as cold water has a relatively higher density than warm water. 4Fishes Certain group of fishes uses Archimedes’ principles to go up and down the water. To go up to the surface, the fishes will fill its swim bladder (air sacs) with gases (clever isn’t it?). The gases diffuse from its own body to the bladder and thus making its body lighter. This enables the fishes to go up. To go down, the fishes will empty their bladder, this increases its density and therefore the fish will sink.