Introduction of Physics

1
Introduction of Physics

• Shatin Tsung Tsin Secondary School
• Mr. C.K. Yu
• Mr. Tai Kin Fai

2
What is Physics? Extracted from New Physics at
Work, book 1A

• Physics is the scientific study of matter and
  energy and the relations between them. Microwave
  oven, mobile phone, seat-belt and crumple zone in
  safe car design, X-rays machine, and nuclear
  reactor are but a few of the appliances/devices
  that we encounter in daily life that draw on
  physics principles for their design.
• The study of physics helps us develop a
  scientific way of working and problem solving,
  e.g, proposing hypotheses and testing them
  against observations. It also helps us to develop
  a set of values and attitudes such as curiosity,
  honesty, respect for evidence, appreciation of
  achievement in physics and recognition of
  limitations.

3
Introduction

• What is Physics?
• 2) What is needed before a microwave oven is
  invented or designed?
• 3) What do you expect after studying physics?

Physics is the scientific study of matter and
energy and the relations between them.
A physics principle for its design is needed.
It helps develop a set of values and attitudes in
physics and recognition of limitations.
4
Objectives of Studying Physics

1. Able to make observation
2. Able to understand how things behave in the
   observation
3. Able to understand what laws and theories about
   an observation
4. Able to apply the laws and theories in solving
   related problems

5
Steps of scientific study of physics

1. Observation (how things behave in our daily life
   )
2. Data collection (experiment measurement, data
   recording)
3. Data analysis (numerical analysis, graphical
   analysis)
4. Conclusion (Laws, Theories and Principles )

6
1st Activity

• Your teacher will throw an object. Observe and
  draw a diagram to show what you saw.

the object
7
Observation

• After the object left teachers hand, it moved
  faster/slower and faster/slower upwards.
• After it reached the highest/lowest point, it
  moved faster/slower and faster/slower downwards.

8
Data Collection

• Your teacher will throw the object three times.
  The object will return to his hand. Measure and
  record the following quantities with your
  group-mates.

Time to highest position Total Time
1
2
3
9
Simple Data Analysis

• Analyze the data, discuss with your group-mates
  and make a conclusion about the measurement.

10
Conclusion

• Make a conclusion about the relation of the two
  time measurements.
• (about, approximate, exactly, twice)
• _________________________________
• _________________________________
• _________________________________
• _________________________________
• _________________________________

The total time is about twice the time to the
highest position. The time to the highest
position is about the same as the time returning
to his hand from the highest position.
11
Summary of Introduction

• We learn the following steps in scientific study
  of Physics.

• Observation
• Data Collection
• Data Analysis
• Conclusion

?
?
?
?
12
2nd activity

• Your teacher will throw an object again, sketch
  (????) how the object moves/flies.

13
2nd activity

• Now, your teacher will do the activity several
  times.
• Discuss with your group-mate what you will
  measure first and put down the quantities in the
  table.
• Make some measurements and record in a table.

14
2nd activity
Length of string Total time for ten cycles
1
2
3
4
5
15
2nd activity

• What is the length of the string so that it takes
  1 second to complete one cycle?
• Do you know how to analyze these data to find the
  answer of this question?
• This procedure is called Data Analysis. Lets
  look at the way to analyze the data in next
  lesson.

16
Scientific Method of Study

• The steps of scientific study of physics that you
  learned in previous lessons.
• Observation
• Data ___________
• Data ____________ Graphical Method
• ________________

Collection
Analysis
Conclusion
17
Data Collection

• Data can be collected during observation or
  experiment.
• Most often, data are collected during experiment
  as experiment can be better controlled.

18
Data Collected
Length of string /cm Time for 10 cycles / s Average time for 1 cycle /s
1
2
3
4
5
19
Data Collection

• 1) Why is it better to take the total time for 10
  cycles?
• __________________________________
• 2) How many times of measurement or repetitions
  are necessary?
• __________________________________

To reduce the reaction time error.
At least three times. The more the better.
20
Graphical Data Analysis

• Data can be analysed numerically
  (nu/me/ri/cal-adj., nu/me/ri/cal/ly-adv.)
  or/and graphically. We will use graphical method
  to find out the relation between two quantities,
  e.g. in the previous activity.
• the length of string
• average time for 1 cycle

21
Graphical Data Analysis

• x is used to represent the first quantity and
  y ______________.

the second
The name of the graph could be either The graph
of relationship between __ and y Or The graph
of y against ___
X
X
22
Graphical Data Analysis
y
The graph of y against x

x
23
Graphical Data Analysis

• Plotting (??) a graph means drawing a graph with
  some sets of values of x and y.
• The values x and y may be the data collected in
  daily life or in experiments. For example, x
  represents the length of string and y the time
  for one cycle.

24
Graphical Data Analysis
Length of string/m Average time for 1 cycle/s
1 0.85 2.16
2 0.73 1.70
3 0.64 1.60
4 0.35 1.18
How many sets of data are there in the above
table? Ans There ___________ sets of data.
are four
25
Graphical Data Analysis
The graph
26
Graphical Data Analysis
The graph
27
Graphical Data Analysis

• A straight line or a curve can be drawn to show
  the relation between the two quantities.
• A straight line represents the simplest relation.
  
• If the line is a straight line, then y and x have
  a linear relationship.

28
Graphical Data Analysis
The graph of y against x
x length of string y average time The
mathematical equation to represent the linear
relationship between two quantities is y
m x c
29
Graphical Data Analysis
The graph of y against x
m is the slope (??) of the graph. c is the
y-intercept (y ???)
30
Graphical Data Analysis
If c is zero,. i.e. the line passes the origin
(0,0) , then y is directly proportional to
(?????) x, and m is the proportional constant
(????).
The graph of y against x
31
Find the slope, m (2 points form)

• On the graph line, choose two points.
• Their locations are (x1, y1) and (x2, y2).
• (x1, y1) is the first point and (x2, y2) is the
  second point

• Draw a right-angled triangle as shown in the
  diagram.

3.The slope, m, can be calculated by the
following formula
Dy y2-y1
(x1,y1)
y1
Dx x2-x1
(D, delta difference in- )
x1
32
Example 1
What is the slope of the following graph ?

• Steps
• Two points (2, 5) and (10,9) are chosen.
• 2. A triangle is drawn.
• 3. By two points form

33
Class Practice

1.
8-6 10-4

The slope, m
34
Class Practice

2.
1.
14-8 18-6

The slope, m
35
Example 1 Discussion
Will there be any difference if (10,9) is the
first point and (2,5) the second point in example
1 ?
36
Example
A spring (??)was loaded with weights (W) in g.
The length of the spring (L) is measured for each
different load.
Load, W (g) 20 40 60 80 100
Length of Spring, L (cm) 16.0 20.0 24.5 28.0 31.5
Objective To find an equation to describe the
relationship between W (load) and L (length of
spring).
37
(20, 16.0)
The graph of length of spring against load
(40, 20.0)
35
(60, 24.5)
30
(80, 28.0)
25
(100,31.5)
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
38
Does the line pass through all points ? Ans ___
No
The y-intercept is about _____cm
12.3
The slope
0.195
The equation to describe the relationship is L
0.195 W 12.3
39
Equation L 0.195 W 12.3
Discussion What is the original length of the
spring without being loaded? Answer
____________ What is the length of the spring if
it is loaded with 200 g? Answer _____________
12.3 cm
51.3 cm
(L 0.195 x 200 12.3)
40
Drawing the Best Fit Line
The graph of length of spring against load
Which line is the best?
35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
41
Drawing the Best Fit Line

• Steps of drawing the best line.
• From the data, find the mean values of both W and
  L (60, 24)

W (20406080100)/5 60
L (162024.52831.5)/5 24
42
Drawing the Best Fit Line

• Steps of drawing the best line.
• From the data, find the mean values of both W and
  L (60, 24)
• On the graph paper, plot the mean point of
  (60,24).

43
Drawing the Best Fit Line

• Steps of drawing the best line.
• From the data, find the mean values of both W and
  L (60, 24)
• On the graph paper, plot the mean point of
  (60,24).
• Draw a straight line passing through the mean
  point, and adjust the line so that data points on
  both sides of the mean points should be evenly
  distributed (?????) around the straight line.

44
Summary of Graphical Analysis
45
Summary of Graphical Analysis
The graph of length of spring against load
1) Write the name of the graph (e.g The graph of
Length of spring against load)
46
Summary of Graphical Analysis
The graph of length of spring against load

1. Write the name of the graph (e.g The graph of
   Length of spring against load)
2. Select the vertical axis (Y-axis) and horizontal
   axis (X-axis), draw an arrow on each axis and
   label the two axes (Length of spring/cm, load/g)

length of spring /cm
load /g
47
Summary of Graphical Analysis
The graph of length of spring against load

1. Write the name of the graph (e.g The graph of
   Length of spring against load)
2. Select the vertical axis (Y-axis) and horizontal
   axis (X-axis), draw an arrow on each axis and
   label the two axes (Length of spring/cm, load/g)
3. Properly draw the scale on the two axes

35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
48
Summary of Graphical Analysis
The graph of length of spring against load

1. Write the name of the graph (e.g The graph of
   Length of spring against load)
2. Select the vertical axis (Y-axis) and horizontal
   axis (X-axis), draw an arrow on each axis and
   label the two axes (Length of spring/cm, load/g)
3. Properly draw the scale on the two axes
4. Plot the data points on the graph paper

35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
49
Summary of Graphical Analysis
The graph of length of spring against load

1. Write the name of the graph (e.g The graph of
   Length of spring against load)
2. Select the vertical axis (Y-axis) and horizontal
   axis (X-axis), draw an arrow on each axis and
   label the two axes (Length of spring/cm, load/g)
3. Properly draw the scale on the two axes
4. Plot the data points on the graph paper
5. Find the mean values of all data for both
   horizontal and vertical axes (W 60, L 24)

35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
50
Summary of Graphical Analysis
The graph of length of spring against load

1. Write the name of the graph (e.g The graph of
   Length of spring against load)
2. Select the vertical axis (Y-axis) and horizontal
   axis (X-axis), draw an arrow on each axis and
   label the two axes (Length of spring/cm, load/g)
3. Properly draw the scale on the two axes
4. Plot the data points on the graph paper
5. Find the mean values of all data for both
   horizontal and vertical axes (W 60, L 24)
6. Locate and plot the mean point (60,24)

35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
51
Summary of Graphical Analysis

1. Find the mean values of all data for both
   horizontal and vertical axes (W 60, L 24)
2. Locate and plot the mean point (60,24)
3. Draw a straight line to pass through the mean
   point. Ensure that there are points above and
   below the straight line on both sides of the mean
   point.

The graph of length of spring against load
35
30
25
20
length of spring /cm
15
10
5
0
0
20
40
60
80
100
120
load /g
52
Summary of Graphical Analysis

1. Find the mean values of all data for both
   horizontal and vertical axes (W 60, L 24)
2. Locate and plot the mean point (60,24)
3. Draw a straight line to pass through the mean
   point. Ensure that there are points above and
   below the straight line on both sides of the mean
   point.
4. Extend the line to the y-axis, find the
   y-intercept, c.

The graph of length of spring against load
35
30
25
20
length of spring /cm
15
12.3
10
5
0
0
20
40
60
80
100
120
load /g
53
Summary of Graphical Analysis

1. Draw a straight line to pass through the mean
   point. Ensure that there are points above and
   below the straight line on both sides of the mean
   point.
2. Extend the line to the y-axis, find the
   y-intercept, c.
3. On the straight line, locate two points and find
   the slope m with the method of two-point form.

The graph of length of spring against load
35
30
25
20
length of spring /cm
15
12.3
10
5
0.195
0
0
20
40
60
80
100
120
load /g
54
Summary of Graphical Analysis

• Draw a straight line to pass through the mean
  point. Ensure that there are points above and
  below the straight line on both sides of the mean
  point.
• Extend the line to the y-axis, find the
  y-intercept, c.
• On the straight line, locate two points and find
  the slope m with the method of two-point form.
• Complete the equation.
• y m x c

The graph of length of spring against load
35
30
25
20
length of spring /cm
15
12.3
10
5
0
0
20
40
60
80
100
120
load /g
55
Summary of Graphical Analysis

• Draw a straight line to pass through the mean
  point. Ensure that there are points above and
  below the straight line on both sides of the mean
  point.
• Extend the line to the y-axis, find the
  y-intercept, c.
• On the straight line, locate two points and find
  the slope m with the method of two-point form.
• Complete the equation.
• L 0.195W12.3

The graph of length of spring against load
35
30
25
20
length of spring /cm
15
12.3
10
5
0
0
20
40
60
80
100
120
load /g
56
Practice 1

• For the data in the following table, plot y
  against x and draw the best straight line graph
  and find the slope and the equation to describe
  the relationship between x and y.

x 1 2 3 4 5
y 3 5 7 9 11
57
Practice 2

• For the data in the following table, plot S
  against t and draw the best straight line graph
  and find the slope and the equation to describe
  the relationship between S and t.

t 20 40 60 80
s 36 46 56 66
58
Practice 3

• In an experiment, the temperature (T/oC) of
  alcohol is recorded at different time (t /min)
  and the results are recorded in the table below.

t/min 10 15 20 25 30
T/oC 15 13 10 7 5
59
Curve Fitting a Line or a Curve
The graph of s against t
35
30
25
20
S
15
10
5
0
0
2
4
6
8
10
12
14
16
18
t
60
Curve Fitting a Line or a Curve
A line may be drawn but the points are quite far
away from the graph.
But the points are quite close to the curve.
61
Curve Fitting a Line or a Curve
In this situation, a curve is better than a line.
But s and t is not linear related.
62
Discussion

• How is the best fit line drawn ?

63
End of Introduction

• Thank you !!