# 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.

#### 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.

## 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.
• 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.

### 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.