Title Unit 1 - Motion, Forces & Energy - Cambridge - Dr.Eman Salama.pdf ✅

Unit 1 Motion, Forces & Energy
Unit 1: Motion, Forces & Energy – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 Page 1 Introduction Measurements & Density Physics is the science of measurement. A physical quantity is any quantity that can be measured (has value & unit). Units of measurement: All physical quantities must be expressed with at least a magnitude (numerical value) and a unit of measurement. Examples of physical quantities and their definitions: 1. The mass of an object is the amount of matter contained in this object. The mass is usually measured in kilograms/grams using a balance (such as spring balance, beam balance or top pan balance). 2. The volume of an object is the amount of space occupied by this object. The volume is usually measured in cubic meter (m3 ), cubic centimeter (cm3 ), cubic decimeter (dm3 ) or litre (l).  Volumes of regular solids can be calculated by taking measurements with a ruler then using mathematical formula.  Volumes of irregularly shaped objects can be found using the displacement method. Figure (a) shows how we may use a measuring cylinder to find the volume of a small irregular object. Figure (b) shows how a displacement can may be used to find the volume of a larger object. (a) (b)
Unit 1: Motion, Forces & Energy – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 Page 2 Important Precautions: 1. The measuring cylinder should be placed on a flat horizontal surface. 2. Look perpendicular to the scale of the cylinder to avoid “parallax” error. 3. The object must be completely submerged in water. If the object floats in water (less dense than water) therefore a metal sinker is used to submerge it. 4. Tie a string round the object and lower it gently to avoid splashing of water (which will reduce the volume of water & cause an error). How to avoid parallax error?!’ Observer reads the bottom of the meniscus Place the object as close to the edge of the And looks perpendicular to the scale. Ruler as possible. 3. The density is the mass per unit volume of a substance. Density = Mass Volume ρ = m v Where ρ is the Greek letter rho. Density is measured in g/cm3 or kg/m3 , where 1 g/cm3 = 1000 kg/m3 (density of water).  Density tells us how closely packed the particles are.  So, is steel heavier than wood?! When comparing heaviness of materials we must take the same volume of those materials, to have a fair comparison. Accordingly, the greater the mass per unit volume; the higher is the density of this material.
Unit 1: Motion, Forces & Energy – IGCSE Physics 0972 – Dr. Eman Salama +201271111553 Page 3 Density is the reason behind floating:  Ice is less dense than water (icebergs float in the sea).  Hydrogen and helium are much less dense than air (they are used for filling balloons that float upwards). Powers of ten: “very small and very large numbers” Prefixes are used to give multiples and submultiples. The prefix represents a power of ten. The standard multiples and submultiples are mostly in steps of 103 . These prefixes are not units of measurement. They are just used to express physical quantities that are too big or too small (they only come before a unit). Symbol Prefix Value n nano 10-9 μ micro 10-6 m milli 10-3 c centi 10-2 k kilo 103 M mega 106 G gega 109 Conversions: “When going from large to small we multiply and when going from small to large we divide” Example 1: how many seconds are there in 10 hours? Tip: going from large to small we multiply, so: 10x60 minutes x 60 seconds= 36000 seconds Example 2: how many kilograms are there in 5630000 milligrams? Tip: going from small to large we divide, so 5630000 ÷ (1000 × 1000) = 5.63 kilograms.