Mechanics Chapter 1 units, base & derived quantities

Mechanics, Units, Base Quantity, Derived Quantity, Physics

1. Intro: What is Mechanics?
1

2. What is Mechanics?
2
▰Mechanics is the branch of Physics dealing with the
study of motion
▰Motion is a fundamental idea in all of science.
▰Mechanics can be divided into 2 areas:
1.Kinematics, dealing with describing motions
2.Dynamics, dealing with the causes of motion

3. CHAPTER
UNITS AND PROBLEM SOLVING
3
1

4. CHAPTER OBJECTIVE
▰Distinguish standard unit and system units
▰Describe the SI and specify the references for the three main base quantities of
this system
▰Use common metric prefixes and nonstandard metric units
▰Explain conversion factor relationships and apply them in converting units
within a system
▰Determine the number of significant figures
▰Establish a problem-solving procedure and apply it to typical problems
4

5. Quantitative Observations
What can be measured with the
instruments on an aeroplane?
Qualitative Observations
How do you measure artistic
beauty?
Observation: Quantitative vs qualitative
•Most observation in physics are quantitative
•Descriptive observations (or qualitative) are usually imprecise

6. ▰To be quantitative in Physics requires measurements
▰How tall is Ming Yao? How about his weight?
▻Height: 2.29 m (7 ft 6 in)
▻Weight: 141 kg (310 lb)

Number + Unit
▰Unit officially accepted – standard unit
▰A group of standard unit/combination – system of units
▰Both numbers and units necessary for any meaningful
physical quantities


Why & How We Measure: Physical Quantities

7. Are classified into two types:
1.Base quantities
2.Derived quantities
Physical Quantities
Base quantity
is like the brick – the
basic building block of
a house
Derived quantity is like
the house that was
build up from a collection
of bricks (basic quantity)

8. ▰Many possible choices for units of Length, Mass, Time (e.g.
Yao is 2.29 m or 7 ft 6 in.)
▰In 1960, standards bodies control and define System
Internationale (SI) unit:
Eg.
▻LENGTH: Meter
▻MASS: Kilogram
▻TIME: Second
SI UNITS

9. BASE QUANTITIES & SI UNITS
Base Quantities Name of Unit Symbol of Unit
Length metre m
Mass kilogram kg
Time second s
Electric Current ampere A
Temperature kelvin K
Amount of Substance mole mol
Luminous Intensity candela cd

10. SI Length Unit: Meter
▰Length describe the quantity of space such width, height or
distance
▰Symbol  [L]
▰Current Definition of 1 Meter: the distance traveled by light
in vacuum during a time of 1/299,792,458 second.
▰1 Meter = about 3.28 ft
▰1 km = 1000 m, 1 cm = 1/100 m, 1 mm = 1/1000 m

11. SI Time Unit: Second
▰Time describes the flow of the universe from the past through
the present into the future. In physics, usually mean a quantity
of time in seconds, such as 35s.
▰Symbol  [T]
▰The solar clock was originally used to define the second.
▰1 Second is defined in terms of an “atomic clock”– time taken
for 9,192,631,770 oscillations of the light emitted by a
cesium-133 atom.

12. Atomic Clock
▰Louis Essen (right) and
Jack Parry (left) standing
next to the world's first
caesium-133 atomic clock

13. SI Mass Unit: Kilogram
▰Mass describes the quantity of matter
▰Symbol  [M]
▰1 Kilogram – the mass of a specific platinum-
iridium alloy kept at International Bureau of
Weights and Measures near Paris. Copies are
kept in many other countries.
▰Yao Ming is 141 kg, equivalent to weight of 141
pieces of the alloy cylinder.

14. Length, Mass, Time

15. Prefixes for SI Units
Multiple

Prefix

Symbol
10
18
exa E
10
15
peta P
10
12
tera T
10
9
giga G
10
6
mega M
10
3
kilo k
10
2
hecto h
10
1
deca da
Prefixes are used to denote very big or
very small numbers

16. Multiple

Prefix

Symbol
10
-1
deci d
10
-2
centi c
10
-3
milli m
10
-6
micro µ
10
-9
nano n
10
-12
pico p
10
-15
femto f
10
-18
atto a
Prefixes for SI Units

17. Prefixes for SI Units
Multiple

Prefix

Symbol
10
18
exa E
10
15
peta P
10
12
tera T
10
9
giga G
10
6
mega M
10
3
kilo k
10
2
hecto h
10
1
deca da
3,000 m = 3  1,000 m

= 3  10
3
m = 3 km
1,000,000,000 = 10
9
= 1G
1,000,000 = 10
6
= 1M
1,000 = 10
3
= 1k

141 kg = ? g
1 GB = ? Byte

18. Multiple

Prefix

Symbol
10
-1
deci d
10
-2
centi c
10
-3
milli m
10
-6
micro µ
10
-9
nano n
10
-12
pico p
10
-15
femto f
10
-18
atto a
Prefixes for SI Units 0.003 s = 3  0.001 s

= 3  10
-3
s = 3 ms
0.01 = 10
-2
= centi
0.001 = 10
-3
= milli
0.000 001 = 10
-6
= micro
0.000 000 001 = 10
-9
= nano
0.000 000 000 001 = 10
-12


1 nm = ? m
3 cm = ? m

19. Derived Quantities and Units
▰Multiply and divide units just like numbers
▰Derived quantities: area, speed, volume, density ……
▻Area = Length  Length SI unit for area = m
2
▻Volume = Length  Length  Length SI unit for volume = m
3
▻Speed = Length / time SI unit for speed = m/s
▻Density = Mass / Volume SI unit for density = kg/m
3

▰In 2008 Olympic Game, Usain Bolt sets world record at 9.69 s in Men’s
100 m Final. What is his average speed ? m/s 10.32
s
m
9.69
100
s 9.69
m 100
speed 

20. Exercise:
•Work out the derived quantities for:
Defining equation: velocity =
In terms of units: Units of speed =
Defining equation: acceleration =
In terms of units: Units of acceleration =
Defining equation: force = mass × acceleration
In terms of units: Units of force = time
distance time
velocity

21. 21
THANKS!
Any questions?
You can find /Whatsapp me