MEASUREMENT A simple definition of physics is “the science of measurement”
Measuring- For a measurement to be useful it must: – be accurate – have a unit.
Basic measurements in physics • Length:- Including areas and volumes • Mass • Time • Temperature etc.
TimeTime allows change to happen.Measuring instruments:• Stop watch.• Electronic timer (for very short times).Unitsseconds (s), minutes (m) and hours(h or hrs) (multiply each time by 60 touse the smaller measure)
TemperatureTemperature measures howhot or cold an object is.Measuring instrument:• Thermometer.Unitdegrees Celsius (0C)Degree Fahrenheit (0F)
LengthMeasuring instruments:• Tape measure• Metre stick• Opisometer (for small curves)• Trundle wheel (for longer distances) Units metres (m) or centimetres (cm)
Opisometer (for small curves)• most commonly used to measure the lengths of roads, rivers and other line features on maps.• Opisometers designed for this purpose provide scales reading the measured distance in
The trundle wheel• a simplified form of surveyors wheel• commonly used by school children• an easy way to find the rough distance• The trundle a clicking device which is triggered once per revolution of the wheel• are not as accurate as other methods• but are a good way to get a rough estimation of a fairly long distance over a good surface.
Mass DEFINITIONMass- the amount of matter an object hasMatter- something that has mass and takes up space.
Units for Measuring Mass• SI Unit- Kilogram (kg) or gram (g)• 1 paper clip= 1 gram• 1000g=1 kilogram• The average human adult weighs 75kg.• Mass cannot be changed by the location, shape and speed of the body.• Large masses are measured in tonnes while small masses are measured in grams.
Examples of Masses of objects Mass in Object kilogram (kg) Electron 10-30 A fine grain of sand 10-6 A pea 10-3 An apple 10-1 A medium-sized car 103 Earth 1024 Sun 1030
WeightSpring Definition- Weight is a gravitational force acting onbalance an object Formula- W = mg where m is the mass of the object g is the gravitational force Units- Weight is measured in newtons (N)
Gravitational FieldThe gravitational field is a regionin which a mass experiences aforce due to gravitationalattraction.
Pretend That You Are in space! Oh where, oh where, has my weight gone? Oh where, oh where can it be? You are floating around. You drift over to a floating scale and put your feet on it. Your feet do not push down on the scale at all. The scale shows that you weigh 0. You have lost your weight—but did you lose your mass?
All my body parts arestill together — so I still have mass!
On a space flight, yourmass would be the same;but your weight wouldchange.
Summing up Mass and Weight• Your MASS is the amount of material in your body.• Your MASS doesn’t depend on where you are.• Your WEIGHT is how much your body pushes down on a scale.• Your WEIGHT depends on how much MASS you have and where you are.
Remember,• Gravity describes the pull between masses.• You have mass, and the earth has mass.• There is a pull between you and the earth.• We measure this pull with a scale.• The more the gravity, the greater the squeeze on the springs of the scale…and the more you weigh.
Gravity and Weight Summary• Your weight on earth is a measure of the GRAVITY pull between you and the earth.• Bodies with more MASS produce a greater GRAVITY pull on each other.
On Earth So, if I ate a lot of yummy tuna fish while standing on the scale, I would gain mass.The pull betweenthe earth and me would become greater—and Iwould weigh more!
Back to the Moon During my trip tothe moon, my mass does not change, but the moon hasmuch less mass than the earth.
Still on the Moon! There is less gravity pullbetween you and the moon.If you stood on the scale on the moon—you would weigh less than on earth!
Differences between Weight and Mass Weight Mass• pull of gravity on • amount of matter in the body the body• units are newtons • units are kilograms, & dyne grams• changes from place • is constant regardless to place of place or location• measure with the • measure with the help of spring help of beam balance balance
VOLUME: What Is Volume? Space occupied by an object is known as its volume. It is denoted by ‘V’
Units Of Volume Volume is measured in cubic centimetres. Also called centimetre cube (cm3) Bigger unit of volume is cubic metre or meter cube (m3)
Volume of Liquids Volume of liquid is measured using measuring vessels. Its unit is litre and smaller unit is millilitre. 1 litre = 1000 ml 1 litre = 1000 cubic cm So, 1 ml = 1 cubic cm
How to measure VOLUME of liquids We will be using graduated cylinders to find the volume of liquids and other objects. Read the measurement based on the bottom of the meniscus or curve. When using a real cylinder, make sure you are eye-level with the level of the water. What is the volume of water in the cylinder? _____mL
What causes the meniscus?A concave meniscus occurs when themolecules of the liquid attract thoseof the container.The glass attractsthe water on the sides.
VOLUME of solids having regular geometric shapesVolume of solids having regulargeometric shapes can bedetermined using differentformulae.
Cube Formula to find volume of a cube is- L x L x L = L3So,volume of the cube = 1cm X 1cm X 1cm = 1 cm3
Volume of Cuboids.Look at theadjacentcuboid:We must first calculate the area of thebase of the cuboid:The base is a rectangle measuring 10cmby 3cm: 10cm 3cm
10cm 3cmArea of a rectangle = length x widthArea = 10 x 3Area = 30cm2We can place 30 cubic centimetres on the base:
4cm 3cm 10cmWe have now got to find how many layersof 1cm cubes we can place in the cuboid:We can fit in 4 layers.Volume = 30 x 4Volume = 120cm3That means that we can place 120 of ourcubes measuring a centimetre in all directionsinside our cuboid.
4cm 3cm 10cmWe have found that the volume of the cuboid is givenby: Volume = 10 x 3 x 4 = 120cm3 This gives us our formula for the volume of a cuboid: Volume = Length x Width x Height
The diagram shows a cuboid. Work out the volume, in cm3, of the cuboid.
Volume of Irregular Objects• For example: a rock!• When objects do not take on a regular shape or it is difficult to measure their dimensions we use a different method to find their volume, this method is called water displacement
Displacement is:– The amount of water an object replaces is equal to the object’s volume How to use the method of water displacement?
Measuring the volume of anirregularly shaped object that sinks in water Graduated cylinder Stone
Measuring the volume of anirregularly shaped object that floats in water Graduated Overflow Cylinder can Thread Cork
Story of a naked man In the first century BC the Romanarchitect Vitruvius related a story of howArchimedes uncovered a fraud in themanufacture of a golden crown commissionedby Hiero II, the king of Syracuse. The crown(corona in Vitruvius’s Latin) would have been inthe form of a wreath. Hiero would have placedsuch a wreath on the statue of a god orgoddess. Suspecting that the goldsmith mighthave replaced some of the gold given to him byan equal weight of silver, Hiero askedArchimedes to determine whether the wreathwas pure gold. And because the wreath was aholy object dedicated to the gods, he couldnot disturb the wreath in any way.
ArchimedesThe solution which occurred when hestepped into his bath and caused it tooverflow was to put a weight of goldequal to the crown, and known to bepure, into a bowl which was filled withwater to the brim. Then the gold wouldbe removed and the king’s crown put in,in its place. An alloy of lighter silverwould increase the bulk of the crownand cause the bowl to overflow.
Does something that isbigger always have more mass?
What is density?• Density is a comparison of how much matter there is in a certain amount of space.Definition- Density is defined as mass per unit volumeFormula- mass/volumeS I units- kg/m 3 MOther units- g/cm3 D V My Dear Valentine
Density Density Sink Object Mass/g Vol/cm 3 or g/cm3 Float?Aluminium 50 18.52 2.70 Sink sheet Gold 150 7.89 19.0 Sink bracelet Water 500 500 1 --- Ice 10 10.87 0.92 FloatBlock of 0.5 Float 800 1600pinewood