SCIENCE - Motion and Measurement of Distances -

Story of Transport

· Man learnt to domesticate animals and ride them for hunting and to move from one place to another.

· The wheel was invented around 3,500 BC. This led to the discovery of the modern transport system.

· 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 developed further.

M 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 a unit.

· The result of a measurement is expressed in two parts:

i. A number.

ii. A unit of measurement.

· The units of measurement used in ancient times were Length of the foot, width of the finger, cubit and hand span.

· Measurements done with body parts of different human beings differed because of differing sizes of the body part.

· Therefore, for the sake of uniformity, the International System of Units (SI units) was adopted as the most widely used system of measurement.

Measurement of Length

· The SI unit of length is metre.

· 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 measuring tape.

· The length of a curved line can be measured using a thread.

Motion

· Motion refers to the change in the position of an object with respect to time.

· Objects are at rest or in motion.

There are two states of an object:

Rest

Motion

When the body does not change its position with respect to time, then it is said to be at rest, or it is said to be

motionless or stationary.

When the body changes its position with respect to time, then it is said to be in motion.

Example: Chairs of the dining table, a flower vase, the table and the blackboard are all at rest.

Example: The blades of a rotating fan, the hands of a working wall clock, a moving car, a spinning top and satellites are all in

motion.

Types of Motion

Rectilinear Motion

· Rectilinear motion is the motion of an object which moves in a straight line.

· Examples: A train moving on a track, a parade and coins tossed in the air.

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 circular path.

· Examples: The hands of a clock, a merry-go-round, the blades of a fan, the wheels of a moving vehicle, satellites and a spinning top.

Periodic Motion

· Periodic motion is the motion which repeats itself at regular intervals of time.

· Examples: The pendulum of a wall clock, the bells in a church, a bouncing ball, a vibrating string and a swinging cradle.

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 circular motions.

· 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 periodic motions.

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 hand-span.

· 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 hand-span 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 (‘System International ’Units’ 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.