Motion and Measurement of Distances
Story of Transport
• Man learnt to domesticate animals and ride them for hunting and to move from one place toanother.
• The wheel was invented around 3,500 BC. This led to the discovery of the modern transportsystem.
• By using horses and wheels, the early man discovered the chariot which was the cheapest mode of road transport.
• Early man hollowed tree trunks and used them to cross rivers and streams. This gave rise to waterways.
• Slowly, the modern transport system was developedfurther.
Measurement In Daily Life
• Measurement is a method that enables us to identify the quantity of anything.
• In measurement, we compare the unknown quantity of an object to the known fixed quantity of
an object of the same kind, which leads us to measure the quantity of the unknown object.
• The known fixed quantity in a measurement is called a unit. For example, the length of cloth is
10 metres, so the unit of measurement here is a metre.
• The quantity equals the product of numerical value and the unit. It is written mathematically as:
• Quantity= Numerical Value x Unit
Measurement
• Measurement means the comparison of an unknown quantity with some known quantity.
This known fixed quantity is called aunit.
• The result of a measurement is expressed in twoparts:
(i) Anumber.
(ii) A unit ofmeasurement.
• The units of measurement used in ancient times were: Length of the foot, width of the finger,
cubit and handspan.
• Measurements done with body parts of different human beings differed because of differing
sizes of the bodypart.
• Therefore, for the sake of uniformity, the International System of Units (SI units) was adopted
as the most widely used system ofmeasurement.
Measurement of Length
• The SI unit of length ismetre.
• Each metre (m) is divided into 100 equal divisions called centimetre(cm).
• Each centimetre has 10 equal divisions called millimetre(mm).
• Thus,
1 m = 100 cm
1 cm = 10 mm
1 km = 1000 m
• The length of a straight line is measured by a metre scale or a measuringtape.
• The length of a curved line can be measured using athread.
Precautions while Measuring Lengths using a Metre Scale
• Place the scale in contact with the object along itslength.
• If the zero mark is not clear, use any other full mark of the scale and then subtract the reading
of this mark from the reading at the other end. The difference is the length of theobject.
• Your eye must be exactly in front of the point from where the measurement is to betaken.
Motion
• Motion refers to the change in the position of an object with respect totime.
• Objects are at rest or inmotion.
• There are two states of anobject:
Types of Motion
Rectilinear Motion
• Rectilinear motion is the motion of an object which moves in a straightline.
• Examples: A train moving on a track, a parade and coins tossed in theair.
Circular Motion
• Circular motion is the motion in which an object moves continuously at a fixed distance from a fixed point.
• It is a motion in which the body traverses a circularpath.
• Examples: The hands of a clock, a merry-go-round, the blades of a fan, the wheels of a
moving vehicle, satellites and a spinningtop.
Periodic Motion
• Periodic motion is the motion which repeats itself at regular intervals oftime.
• Examples: The pendulum of a wall clock, the bells in a church, a bouncing ball,
a vibrating string and a swingingcradle.
Combinations of different types of Motion
• A moving car which moves straight on the road displays rectilinear motion, but at the same time,
the wheels of the car which are moving in circles display circular motion. So, a moving car displays both,
rectilinear and circularmotions.
• In a sewing machine, the needle is in periodic motion, whereas the wheels of the sewing machine are
in circular motion. So, a sewing machine displays both, circular and periodicmotions.
Physical Quantities
• The quantities that can be measured are called physical quantities. For measuring the physical quantities,
we require magnitude and a fixed unit. For example, If the distance from London to Reading is 275 km,
so the magnitude is 275 and its unit is km here.
• The specific physical quantities that cannot be expressed in any other quantity are called fundamental
physical quantities. Some fundamental physical quantities are mass, length, time and temperature.
Traditional Units of Measurement:
In ancient times, people use their hands, arms and feet to measure the quantities. These methods still use
in the present time. The units that we measure through these methods are yards, cubit and handspan.
• Yard: The distance between the endpoint of an outstretched arm to the tip of the nose.
• Cubit: The distance between the elbow to the tip of the middle finger.
• Foot: Measurement of the quantity by a barefoot of an adult person.
• Handspan: The measurement of a quantity by the tip of the thumb to the tip of the little finger
when the palm is outstretched.
These methods are not reliable because different people have different body shapes and sizes.
However, if these methods apply individually then they can be effective. For example, tailors use
the handspan method to measure the arm of the customers to make the sleeves.
Standard Units of Measurement:
• The standard units of measurement introduced to measure accurate quantity of any object.
• In 1960, the General Council of Weights and Measures organized where all the scientists gathered
to decide the uniform system of units acceptable all over the world.
• The standard system unit is called the SI system(‘Systeme International d’Unites’ in French).
Table 1 shows the SI units of fundamental quantities.
A few other SI systems are:
• CGS (Centimetre for length, Gram for mass and Second for time),
• MKS (Metre for length, Kilogram for mass and Second for time),
• FPS (Foot for length, Pound for mass and Second for time).
• The measurement of smaller quantities is called submultiples of units. They represent with the
factor of 1/10, 1/100 and 1/1000, etc.
• The measurement of larger quantities is called multiples of units. They represent with the
factor 10, 100 and 1000, etc.
• Both multiples and submultiples have prefixes and symbol.
Table 2 shows the prefixes of multiples and submultiples.
Correct Measurement Of Length
We use suitable instruments to measure the quantity of an object.
Measuring Length
• The measurement of length concerns the length, width, thickness, height and distance of any object.
• There are several instruments used to measure the length. For example, a ruler, metre rod and a measuring tape, etc.
• A ruler has units of centimetre and millimetre. It is used to measure smaller quantities(Figure 2).
Figure 2: A ruler.
A metre rod is used by tailors to measure the length of the cloth. The unit of metre rod is
fixed to one metre(Figure 3).
Figure 3: A metre rod.
• Correct way to use a ruler/scale
• The following steps we need to follow while measuring anything by a ruler/scale:-
• Place the scale exactly at the tip of the object.
• Do not observe the object at different angles while measuring because this causes parallax error(Figure 4).