measurement

By Miss Buicke

OP1Measure length, mass, time and temperature (SI units). Perform simple calculations based on these to find the derived quantities: area and volume.Understand that units of measurement follow the SI system. OP2  Measure mass and volume of a variety of solids and liquids.  

  What we must know from the syllabus

Physics is the science of exact measurement of quanties such as length, mass, time, temperature, area and volume.

There are lots of different units used for measurement. Can we think of any?

Scientists use units called S.I. Units to measure quanties. It is important that S.I units are used. Scientiest all over the world use the same unit of measurement to avoid confusion.

S.I. stands for Système International d'unités. it is in french because it was the French who first promoted this system.

Quantity SI unit Symbol

Length Meter mMass Kilogram KgTime Second sArea Square meter m2Volume Cubic meter m3

quantity SI unit  Symbol

Speed Meters per second

m/s

Temperature Degrees celcius

oC

A ruler is used to measure length.

A measuring tape in used to measure length

A trundle wheel is used to measure the length of large Distances.

An opisometer is used to measure the length ofa curved line.

A balance is used to measure mass

A graduated cylinder is used to measure volume.

           A stop watch is used to measure time

A vernier callipers is used to measure the diameter of  objects.

A thermometer is used to measure temperature

                        Measuring length. The SI unit for length is the metre. But length can also be measured in:

• Millimetres(mm)• Centimetres (cm)• Kilometres (km)

Depending on what we are measuring we use the most appropriate unit.

For example:when measuring the length of your science copy we use centimeters.

When measuring the length of the school yard we use meters

When measuring the driving distance between Dublin and Kerry we use kilometers.

When measuring the thickness of a coin we use millimeters.

Remember:10 mm is the same as 1 cm100 cm is the same as 1m1000m is the same as 1 km

      Quick check:

What could we use to measure the length of a football field?

What could we use to measure the thickness of a key?

What could we use to measure the length of our desks?

What could we use to measure the height of a student?

What could be use to measure the length of a stream on a map?

Sample question 1: Convert 8.6 cm to mm

1cm = 10 mm8.6 cm = 86 mmWe multiply 8.6 by 10 .ie 8.6cm x 10 = 86mm

Sample question 2: convert 67 mm to cm

10 mm = 1 cmWe divide 67 mm by 10 ie. 67mm ÷ 10 = 6.7 cm

Sample question 3: convert 90cm to meters

There are 100cm in 1m10cm = .1 m90cm = .9m

Sample question 4: convert 80 mm to metersSometimes its easier to work in cm, so we convert 80mm to cm first.10mm = 1cm80mm =8cm

Now we know that 100cm = 1m so, 1cm = .01 m therefore .01 x 8 = .08 m

                           Extra questions:Covert 70 mm to cm Answer = 7 cm

Covert 4.5 mm to cm Answer = .45 cm

Covert 72 cm to mm Answer = 720 mm

Covert 83 cm to m Answer = .83 m

Covert 100 mm to m Answer = .1m

Covert 80m to cmAnswer = 8000cm

                Measuring mass:

Mass is the amount of matter an object contains

Mass is measured in grams (g) or kilograms (kg). Small quantities such as the mass of a chemical you would use in an experiment are measured in grams. The kilogram is more suitable for the mass of a person or the mass of a large bag of potatoes.

      I kg = 1000 g

It is important to understand the difference between the words mass and weight. In everyday usage, these words often have the same meaning.In physics, they have a very different meaning.

The weight of an object is the pull of the earth on it.(we will learn about weight later on)

The mass of an object is the amount of matter in it.

For now just remember that weight and mass have different meanings in science.

Sample question 5: convert 500 g to kg1000g = 1kg1g= .001 kg500g x .001 = .5 kg

Sample question 6: convert .8kg to g 1kg = 1000g.8kg x 1000 = 800g

Measuring time

Time is measured using many units, for examplethe second, the minute, the day, the week, the monthand the year.The SI unit for time is the second (s)

How many seconds are there in a day?There are 24 hours in a day. Each hour has 60 minutes and each minute has 60 seconds.24 x 60 x 60 = 86,400 seconds

                               Measuring area

The amount of surface that covers an object is called its area. The unit for area is the centimetre Squared (cm2) or theMetre squared (m2).

Area of a rectangle = length x width

Area of a triangle = ½ base length x perpendicular height

Area of a circle = πr2

Measuring volume

Volume = How much space an object takes up

The unit for volume is the centimetre cubed (cm3) or the metre cubed (m3).

We must be able to calculate the volume of a regular and an irregular object.

Regular shape:

Calculate the volume of this box:

Formula = length x width x height

Length = 6cm, width = 6cm and height = 6cm

6cm x 6cm x 6cm = 216cm3

To find the mass and volume of an irregularly-shaped small stoneTo find the mass - weigh it on an electronic balance. To find the volume:Drop the stone into a graduated cylinder containing water of a know volume and note the new volume.To get the volume of the stone simply subtract the two readings. In this case the volume = 90cm3 – 75cm3 = 15 cm3.