Class 6 Science Chapter 10 Motion and Measurement, Types of Motion, Measurement, Zero Error and Parallax (For CBSE, ICSE, IAS, NET, NRA 2022)

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Motion and Measurement

Motion

  • A body is said to be in motion when there is change in its position with respect to time.
  • When there is no change in the position of the object with respect to time the body is said to be in rest.

Types of Motion

Linear Motion

  • It simply means motion in a straight line.
  • A parade of soldiers, a train moving along a straight line, etc. are some of the examples.
  • This motion is also known as uniform motion or rectilinear motion.

Curvilinear Motion

  • Motion along a curved path is called curvilinear motion.
  • A car moving on a bend is an example of curvilinear motion.

Circular Motion

  • The motion of an object along a circular path is called circular motion.
  • The motion of the earth in its orbit, an artificial satellite orbiting the Earth at a constant height, etc. are the examples of circular motion.
  • Some other examples are motion of a blade of an electric fan, motion of second՚s hand in a clock.
  • The object remains at the same distance from a fixed point in a circular motion.

Rotational Motion

  • It is the motion in which a whole body moves about an axis.
  • Motion of a top is an example of Rotational motion.

Periodic Motion

  • Motion repeated in equal intervals of time.
  • Some of the examples are a rocking chair, a bouncing ball, a vibrating tuning fork, etc.
  • Oscillations of a pendulum, Motion of a swing are some other examples.

Translational Motion

  • It is the motion by which a body shifts from one point in space to another.
  • The motion of a bullet fired from a gun is an example.

Projectile Motion

It is the motion of an object thrown or projected into the air being subjected to only acceleration of gravity.

Projectile Motion

Combination of Two or More Types of Motions

Motion of a Ball on the Ground
  • The ball is rotating about an axis with the axis itself moving along a straight line.
  • Therefore, for a ball on the ground, a rectilinear motion as well as rotational motion are executed.
Motion of Earth

The earth apart from revolving around the sun also executes rotations on its axis.

Motion of Earth

Measurement

  • It is the comparison of an unknown quantity with a known standard quantity.
  • Result has two parts. First part is the number and another part is the unit.
  • Unit is the known quantity used in measurement. For example, if I say my height is 180 cm, then my height is expressed in number as 150 and the unit is centimeter.

Standard Units of Measurement

SI Unit (International System of Units)

  • This is based upon MKS (Meter-Kilogram-Second) System.
  • This is also the most widely used system of measurement in the world.
  • As per SI system:
    • Unit of length is meter
    • Unit of weight is kilogram
    • Unit of time is second
  • Basic quantities for measurement are Length, weight, and time.
  • Those Units that are used for the measurement of larger distances are the multiples of SI unit.

Sub-Multiples of Units

Units used for measuring smaller distances for example milli, centi, deci.

Metre

  • It is the standard unit of length with the symbol m.
A Metre Scale
  • Each metre (m) is divided into 100 equal divisions, called centimetre (cm) .
  • Each centimetre has ten equal divisions, called millimetre (mm) .

  • For measuring large distances kilometre (km) is used.

Least Count

  • A scale is marked in centimetres and millimetres.
  • One can measure correctly upto one millimetre, that is one-tenth of a centimetre which is also called the least count of a (15 cm) scale.

Direct Measurement

  • Measuring some quantity directly is called direct measurement.
  • For example, using a ruler to measure length is known as direct measurement.
  • Direct measurement is weight, distance, and so on.

Indirect Measurement

  • Measuring something by measuring something else.
  • For example, if I want to measure the length of a curve line, first using a thread i can find the length of the curved line and thereafter compare the length on a ruler.
Measuring a Curved Line

Zero Error and Parallax

  • If zero mark is not visible or in case the scale gets broken, it is called Zero Error. Measuring from a different mark must be carried out.
  • The change or displacement in the apparent position of the object when the object is viewed from two different points is called Parallax.
Parallax Error

Ancient Times

  • Goods were carried either on back of the man or on the back of some animals.
  • Man used to move only on foot.

Changes in the Modes of Transport

  • By the invention of wheel.
  • By the invention of steam engine.
  • Steam engines replaced the animal driven carts along with the spread of Railways network. Jet engines helped in making the aircrafts faster.

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