MEASUREMENTMEASUREMENT

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).

Units seconds (s), minutes (m) and hours (h or hrs) (multiply each time by 60

to use the smaller measure)

Temperature

Temperature measures how

hot or cold an object is.

Measuring instrument:• Thermometer.

Unitdegrees Celsius (0C)Degree Fahrenheit (0F)

Length

Measuring instruments:• Tape measure• Metre stick• Opisometer (for small curves)• Trundle wheel (for longer

distances)

Units metres (m) or centimetres (cm)

• 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 kilometers and miles.

Opisometer (for small curves)

• a simplified form of surveyor's 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.

The trundle wheel

Mass

Mass- the amount of matter an object has Matter- something that has mass and takes up space.

DEFINITION

Measuring Devices of Mass

Weights

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

ObjectMass in

kilogram (kg)

ElectronA fine grain of sandA peaAn appleA medium-sized carEarthSun

10-30

10-6

10-3

10-1

103

1024

1030

Definition- Weight is a gravitational force acting on

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)

Weight Spring balance

Gravitational Field

The gravitational field is a region in which a mass experiences a force due to gravitational attraction.

Weight..???

Mass..??? I am

totally confused!

Pretend That You Are in space!

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?

Oh where, oh where, has my

weight gone? Oh where, oh where

can it be?

All my body parts are still together — so I still have mass!

On a space flight, your mass would be the same; but your weight would change.

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.

Where would you weigh the most?

Earth

Moon

OROR

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 between the earth and me would become greater—and I would weigh

more!

Back to the Moon

During my trip to the moon, my mass does not

change, but the moon has much less mass than

the earth.

Still on the Moon!

There is less gravity pull between 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 the body units are newtons & dyne changes from place to place measure with the help of spring balance

amount of matter in the body units are kilograms, grams is constant regardless of place or location measure with the help of beam balance

Space occupied by an

object is known as its

volume.

It is denoted by ‘V’

VOLUME:

What Is Volume?

Units Of Volume

Volume is measured in cubic centimetres.

Also called centimetre cube (cm33)

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

Different types of measuring vessels

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

How to measure VOLUME of liquids

What causes the meniscus?

A concave meniscus occurs when the molecules of the liquid attract those of the container.The glass attracts the water on the sides.

VOLUME of solids having regular geometric shapes

Volume of solids having regular geometric shapes can be determined using different formulae.

Cube

Formula to find volume of a cube is- L x L x L = L3

So,volume of the cube = 1cm X 1cm X 1cm = 1 cm3

Height (H)

Cuboid

Volume of Cuboids.

Look at the adjacent cuboid:

We must first calculate the area of the base of the cuboid:

The base is a rectangle measuring 10cm by 3cm:

3cm

10cm

3cm

10cm

Area of a rectangle = length x widthArea = 10 x 3 Area = 30cm2

We can place 30 cubic centimetres on the base:

10cm

3cm

4cm

We have now got to find how many layers of 1cm cubes we can place in the cuboid:We can fit in 4 layers.

Volume = 30 x 4

Volume = 120cm3

That means that we can place 120 of our cubes measuring a centimetre in all directions inside our cuboid.

10cm

3cm

4cm

We have found that the volume of the cuboid is given by:

Volume = 10 x 3 x 4 = 120cm3

This gives us our formula for the volume of a cuboid:

Volume = Length x Width x Height

Work out the volume, in cm3, of

the cuboid.

The diagram shows a 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

–The amount of water an object replaces is equal to the object’s volume

How to use the method of water displacement?

Displacement is:

Measuring the volume of an irregularly shaped

object that sinks in water

Graduated

cylinder

Stone

Measuring the volume of an irregularly shaped

object that floats in water

Overflow can

Graduated

Cylinder

Thread

Cork

Story of a naked man

In the first century BC the Roman architect Vitruvius related a story of how Archimedes uncovered a fraud in the manufacture of a golden crown commissioned by Hiero II, the king of Syracuse. The crown (corona in Vitruvius’s Latin) would have been in the form of a wreath. Hiero would have placed such a wreath on the statue of a god or goddess. Suspecting that the goldsmith might have replaced some of the gold given to him by an equal weight of silver, Hiero asked Archimedes to determine whether the wreath was pure gold. And because the wreath was a holy object dedicated to the gods, he could not disturb the wreath in any way.

The solution which occurred when he stepped into his bath and caused it to overflow was to put a weight of gold equal to the crown, and known to be pure, into a bowl which was filled with water to the brim. Then the gold would be removed and the king’s crown put in, in its place. An alloy of lighter silver would increase the bulk of the crown and cause the bowl to overflow.

Archimedes

Does something that is bigger always have

more mass?

Does bigger = 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 volume

Formula- mass/volume

S I units- kg/m3

Other units- g/cm3

My Dear Valentine

M

D V

ObjectMass/g

Vol/cm3

Density

g/cm3

Sink or

Float?

Aluminium

sheet50 18.52

Gold bracelet

150 7.89

Water 500 500 ---

Ice 10 10.87

Block of pinewoo

d800 1600

0.92

19.0

1

2.70

0.5

Sink

Sink

Float

Float

Density

Which one is more dense?

Now which one is more dense?

Ways to Affect Density

•Change mass AND keep volume same

•Change volume AND keep mass same

Change Mass AND Keep Volume Same• Increase the mass increase density

• Decrease the mass decrease in density

Which container has more density?

A B

Change Volume AND

Keep Mass Same• Increase the volume decrease density• Decrease the volume increase density

• Which container has more density?

A B

What 2 ways will increase density?

Keep the same mass AND decrease the volumeKeep the

same volume AND increase the mass