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Presentation On Mass, Weight And Density

Published in: Physics
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This PPT is suitable for the IGCSE and O Level Physics students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Mass, Weight and Density For IGCSE and O Level Students
  2. What will you learn in this lesson? • Weight, mass and gravitational field strength • Difference between weight and mass • Motion of objects falling in a uniform gravitational field with and without air/liquid resistance (including reference to terminal velocity) • Density • Density of a liquid, of a regularly shaped solid and of an irregularly shaped solid • Floating of objects on water and floating of liquids over one another
  3. Weight weight — mass x acceleration of free fall W Quantities with notations Weight (W) acceleration due to gravity or acceleration of free fall (g) Gravitational field strength (g) Mass (m) gravitati«mal field strength mg Units Newtons (N) Meters per square second (m/s2) Newtons per Kilogram (N/kg) Kilograms (kg) Definition Gravitational force acting on an object that has mass is its weight The acceleration caused by the pull of earth's gravity. Its value is approximately 9.8 m/s2 close to earth surface Gravitational field strength at a point is the gravitational force exerted per unit mass placed at that point. On earth's surface gravitational field strength is 9.8 N/Kg Tells how much matter an object is composed of
  4. Weight (contd.) 250 Balance is used to compare the unknown weight of an object with known standard weight If weights are equal their masses will also be equal • When the balance has a scale or grams or kilograms, weighing an object means masses are being compared, not weight
  5. Weight (contd.) 1. 2. 3. Why objects fall on ground? Why the objects weigh less when they are on moon? At what speed(s) would be the 1 kg and 5 kg objects free-fall? If there is vacuum If there is air resistance ll.
  6. Motion of Falling Objects (Example of Parachutist) Weight is constant throughout the movement because of the constant gravitational pull by the earth Drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. Drag force depends on velocity air resistance i weight ii paractune When drag is equal to weight, there is no net external force on the object and the vertical acceleration goes to zero. With no acceleration, the object falls at a constant velocity. The constant vertical velocity is called the terminal velocity What is the effect of drag on terminal velocity? Stages ii and iv show the parachutist is moving at terminal velocity Stage iv will have lower terminal velocity than stage ii
  7. Density Density is defined as mass per unit volume. It's Sl unit is kg/m3. Density Formula unit of mass kilogram, kg kilogram, kg gram. g unit of volume cubic metre, m' cubic decimetre, dm' cubic centimetre, cm m density Unit of density kilograms per cubic metre kilograms per cubic decimetre grams per cubic centimetre Density of water I COOkg,'m' I O kg/dm3 I Oglcm'
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  9. Density (contd.) Any object that is less denser than water will float Wöfér Ice is less denser than water. That's why ice- berg despite having a big size floats on water
  10. Measuring Density For regular shaped solids (such as brick): Mass will be measured using balance and volume is calculated using dimensions For irregular shaped solids (such as rock): Mass will be measured using balance and volume is calculated by displacement (discussed in Lesson, Physical Quantities angvleasurement) 988.63
  11. Measuring Density (contd.) For Liquids: Mass of liquid can be measured using by balance and setting the balance at zero by cylinder is empty. Volume is measured using cylinder. 33
  12. Density in Liquids Liquids with different densities floats over one another and form a density tower Oil Liquids float only when they are immiscible (cannot mix). Otherwise they will dissolve and make a solution like squash and water.
  13. Density (Practice Questions) A student is measuring the density of a liquid. He places a measuring cylinder on a balance and records its mass. He then pours liquid into the cylinder and records the new reading on the balance. He also records the volume oftheliquid« Massofemptycylinder 147g Mass ofcflinder *liquid 203 g Volume ofliquid 59 cne Using the results shown, calculate the density ofthe liquid. Theinside ofa sportshaU measures 80m longby40m wide by 15m high, The air in ithasadensity of 1.3kgtm•whenit is cooL a Calcldatethevolume ofthe air in the sports hall, in m'. b Calculate themassofthe air. State the equation you are using.