Screw Gauge

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Chapter 1 Physical Quantities and Units – Length & Time In the quest to understand nature, scientists use physical quantities to describe the world around us. [email protected]

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explains every thing of screw gaugefor cbse school

Transcript of Screw Gauge

Page 1: Screw Gauge

Chapter 1

Chapter 1

Physical Quantities and Units – Length & Time

Physical Quantities and Units – Length & Time

In the quest to understand nature, scientists use physical quantities to

describe the world around us.

In the quest to understand nature, scientists use physical quantities to

describe the world around us.

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measurement of length and time measurement of length and time

accurate measurement accurate measurement

There are two main types of errors:There are two main types of errors:

Random Errors Systematic Errors

State • random • constant

Occurrence

• in all measurements• observers estimate

the last figure of a reading on an instrument

• observers consistently underestimate or overestimate a reading

Remedy• reduced by

averaging a large number of readings

• minimised by method of differences

No measurement is ever perfectly accurate. Even with high precision instruments, some error is inevitable.

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One metre is the distance travelled by light in a vacuum in 1/299792458 of a second.

Q: What is the speed of light?

One metre is the distance travelled by light in a vacuum in 1/299792458 of a second.

Q: What is the speed of light?

measurement of length measurement of length

length length

Length is the measurement of something from one end to the other end.Length is the measurement of something from one end to the other end.

has a SI unit of metre (m)

other units include centimetres (cm), millimetres (mm) and kilometres (km)

has a SI unit of metre (m)

other units include centimetres (cm), millimetres (mm) and kilometres (km)

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measurement of length measurement of length

length length

measuring tape measuring tape

accuracy = 1 mm / 0.1 cm / 0.001 m

Lengths can be measured by using the following:Lengths can be measured by using the following:

accuracy = 1 mm / 0.1 cm / 0.001 m

metre/half-metre rule metre/half-metre rule

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measurement of length measurement of length

Parallax error is due to incorrect positioning of the eye the object is not at the same level as the markings of the

scale

Parallax error is due to incorrect positioning of the eye the object is not at the same level as the markings of the

scale

parallax error parallax error

8.5 cmwrong

8.2 cmwrong

8.3 cmcorrect

The eye must be positioned perpendicularly at the mark on the scale to avoid parallax error.The eye must be positioned perpendicularly at the mark on the scale to avoid parallax error.

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measurement of length measurement of length

zero errorzero error

Many instruments do not read zero exactly when there is nothing being measured.

Reasons include:

Many instruments do not read zero exactly when there is nothing being measured.

Reasons include: instruments are out of adjustment

some minor fault is present in the instrument

instruments are out of adjustment

some minor fault is present in the instrument

Instruments are usually still accurate as long as the zero error is added or subtracted from the reading shown on the scale.

Instruments are usually still accurate as long as the zero error is added or subtracted from the reading shown on the scale.

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engineer’s calipers engineer’s calipers

A pair of engineer’s calipers and ruler are used for measuring the lengths of objects without any flat sides.A pair of engineer’s calipers and ruler are used for measuring the lengths of objects without any flat sides.

measurement of length measurement of length

the jaws are closed until the points just touch the object to be measured

remove the calipers and measure the distance between

the jaws with a ruler.

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Vernier calipers measure small lengths accurately up to 0.01 cm. Vernier calipers measure small lengths accurately up to 0.01 cm.

vernier calipers vernier calipers

measurement of length measurement of length

accuracy = 0.1 mm / 0.01 cm

inside jaws

outside jaws

main scalevernier scale

tail

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reading on main scale (between A and B) = 2.4 cmreading on vernier scale (C) = 0.08 cmactual reading of object = 2.4 + 0.08

= 2.48 cm

vernier calipers vernier calipers

measurement of length measurement of length

main scale (fixed)

vernier scale (movable)

object being measured

A B C

9 mm

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vernier calipers vernier calipers

measurement of length measurement of length

When the two jaws of the vernier calipers touch each other, both zero marks on the main scale and on the vernier scale should coincide.

If not, there is a zero error in the vernier calipers.

When the two jaws of the vernier calipers touch each other, both zero marks on the main scale and on the vernier scale should coincide.

If not, there is a zero error in the vernier calipers.

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supposing observed reading is 3.24 cm, then corrected reading = observed reading – zero error = 3.24 – (+0.01)

= 3.23 cm

measurement of length measurement of length

0 105

zero error = +0.01 cm

main scale (fixed)

vernier scale (movable)

0 1

If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is positive.

If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is positive.

vernier calipers vernier calipers

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supposing observed reading is 4.03 cm, then corrected reading = observed reading – zero

error = 4.03 – (-0.02)

= 4.05 cm

measurement of length measurement of length

0 10

zero error = -0.02 cm

main scale (fixed)

vernier scale (movable)

0 1

If the two jaws touch each other, but the zero marks of the main scale and vernier scale do not coincide as shown below, the zero error is negative.

5

vernier calipers vernier calipers

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micrometer screw gaugemicrometer screw gauge

measurement of length measurement of length

accuracy = 0.01 mm / 0.001 cm

anvil spindle sleeve thimble ratchet

frame

Micrometers measure small diameters or thicknesses.Micrometers measure small diameters or thicknesses.

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micrometer screw gaugemicrometer screw gauge

measurement of length measurement of length

reading on sleeve = 4.5 mmreading on thimble = 0.12 mmactual reading of object = 4.5 + 0.12

= 4.62 mm

thimblesleeve

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measurement of length measurement of length

micrometer screw gaugemicrometer screw gauge

When the anvil and spindle of the micrometer touch each other, the scales should read zero.

If not, there is a zero error in the micrometer.

When the anvil and spindle of the micrometer touch each other, the scales should read zero.

If not, there is a zero error in the micrometer.

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measurement of length measurement of length

micrometer screw gaugemicrometer screw gauge

If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is positive.If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is positive.

supposing observed reading is 2.37 mm, then corrected reading = observed reading – zero error = 2.37 – (+0.02)

= 2.35 mm

supposing observed reading is 2.37 mm, then corrected reading = observed reading – zero error = 2.37 – (+0.02)

= 2.35 mm

} 2 divisions

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measurement of length measurement of length

micrometer screw gaugemicrometer screw gauge

If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative.If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative.

supposing observed reading is 2.87 mm, then corrected reading = observed reading – zero error = 2.87 – (-0.03)

= 2.90 mm

supposing observed reading is 2.87 mm, then corrected reading = observed reading – zero error = 2.87 – (-0.03)

= 2.90 mm

} 3 divisions

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measurement of timemeasurement of time

timetime

has a SI unit of second (s)

other units include years, months, days, hours, minutes and seconds

has a SI unit of second (s)

other units include years, months, days, hours, minutes and seconds

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measurement of timemeasurement of time

Time can be measured by using the following:Time can be measured by using the following:

analogue stopwatch

analogue stopwatch

digital stopwatch

digital stopwatch

clocks clocks

All timing devices make use of some regular process.All timing devices make use of some regular process.

timetime

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measurement of timemeasurement of time

Time can also be measured by using the following simple pendulum.

Time can also be measured by using the following simple pendulum.

oscillations are regularly repeating motions

the period is time in which 1 oscillation occurs

oscillations are regularly repeating motions

the period is time in which 1 oscillation occurs

the period of a simple pendulumthe period of a simple pendulum

pendulum bob tied to

one end of a thread

BA O

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clocks make use of a process which is a regularly repeating motion (oscillations), such as the swing of a pendulum

such oscillations are very regular so period is regular

most modern clocks depend on the vibration of quartz crystals to keep time accurately

in clocks that are wound up, elastic potential energy is stored in coiled springs

clocks make use of a process which is a regularly repeating motion (oscillations), such as the swing of a pendulum

such oscillations are very regular so period is regular

most modern clocks depend on the vibration of quartz crystals to keep time accurately

in clocks that are wound up, elastic potential energy is stored in coiled springs

measurement of timemeasurement of time

pendulum clock (cuckoo clock)

pendulum clockpendulum clock

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used for measuring long intervals of time

most modern watches depend on the vibration of quartz crystals to keep time accurately

the energy that keeps these crystals vibrating comes from a small battery

many watches still make use of coiled springs to supply the needed energy

used for measuring long intervals of time

most modern watches depend on the vibration of quartz crystals to keep time accurately

the energy that keeps these crystals vibrating comes from a small battery

many watches still make use of coiled springs to supply the needed energy

watchwatch

measurement of timemeasurement of time

wrist watch

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A stopwatch is used to measure short intervals of time.A stopwatch is used to measure short intervals of time.

stopwatchstopwatch

accuracy = 0.1 s accuracy = 0.01 s

measurement of timemeasurement of time

stopwatches (analogue and digital) stopwatches (analogue and digital)

When using a digital stopwatch to time a race, the time to the nearest 0.1 s should be given.

When using a digital stopwatch to time a race, the time to the nearest 0.1 s should be given.

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ticker-tape timerticker-tape timer

measurement of timemeasurement of time

An electrical device that makes use of the oscillations of a steel strip to mark short intervals of time.An electrical device that makes use of the oscillations of a steel strip to mark short intervals of time.

steel strip

magnetcoil ticker-tape drawing pin

carbon paper disc6 ~ 12 V a.c.

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ticker-tape timerticker-tape timer

measurement of timemeasurement of time

10-dot tape10-dot tape

as there are 10 spaces on a piece of tape,

time taken for the tape to pass through the timer

= 10 x 0.02 s

= 0.20 s

between 2 consecutive dots, time interval = 1 s / 50 dots

= (1/50) s or 0.02 s

steel strip vibrates 50 times a second; therefore 50 dots are made in a second on the paper tape

steel strip vibrates 50 times a second; therefore 50 dots are made in a second on the paper tape

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e.g.

metre rulehalf-metre rulemeasuring tapevernier calipers

micrometer screw gauge

pendulum clockwatch

stopwatchticker-tape timer

length (m)mass (kg)

time(s)electric current (A)

temperature (K)amount of substance (mol)

luminous intensity (cd)

PrefixesMeasurement

Physical quantitiesare made up of

can be measured with

e.g. of

Numerical values and suitable units

VectorScalar

Base quantitiesBase SI units

TimeLength

micro () 10-6

milli (m) 10-3

centi (c) 10-2

deci (d) 10-1

kilo (k) 103

mega (M) 106

may be

include

usesuch as for

can be measured with

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