IGCSE Physics Chapter 1 Notes
Peter Nui
June 3, 2026
Contents
1 Motion, Forces and Energy 2
1.1 Making Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 Stacking the measurements up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Scalars and vectors (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.1 Distance and displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Summary of quantities with their units . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Adding vectors together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 Vectors that are at right angles with each other . . . . . . . . . . . . . . . . . . . . 10
1.4 Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 Speed and velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.3 Motion graphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.4.4 Mass and weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.4.5 Motion in free-fall without air resistance . . . . . . . . . . . . . . . . . . . . . . . . 23
1.4.6 Falling with air resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.5.1 What is density? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.5.2 Measuring density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.5.3 Floating and sinking (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.6 Effects of forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.6.1 Effects of forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.6.2 Newton’s first law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1.6.3 Newton’s second law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.6.4 Newton’s third law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.6.5 Circular motion (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.6.6 Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.6.7 Moments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.6.8 Centre of gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.7 Momentum (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
1.7.1 Impulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
1.8 Energy, work and power (Calculation are for extended only) . . . . . . . . . . . . . . . . . 47
1.8.1 Brief introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
1.8.2 Kinetic energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
1.8.3 Gravitational potential energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
1.8.4 Conservation of energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
1.8.5 Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
1.8.6 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
1.8.7 Efficiency (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
1.9 Energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
1.9.1 Energy from the Sun (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . 55
1.9.2 Energy from fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
1.9.3 Energy from water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
1.9.4 Geothermal power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
1.9.5 Nuclear fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
1.10 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
1
,1 Motion, Forces and Energy
1.1 Making Measurements
What are we measuring?
In Physics, there are three quantities that you are measuring: Mass, length and time, other
important quantities include volume, current, etc.
Measuring length We typically use a ruler to measure length and volume. Rulers can typically
measure the size of objects in units of mm or cm.
Other equipment that we can use include trundle wheel and a tape measure, which can be used
to measure longer distances, typically in metres!
Figure 1: Ruler
Figure 2: Tape measure
Figure 3: Trundle wheel
However, not all of them are suitable for measuring every object! For example, it would not be
suitable to measure the height of someone using a ruler, nor is it suitable to use a trundle wheel to
measure the size of a rice grain!
2
,Example Refer to the diagram below, calculate the diameter of the circle
Figure 4: Worked Exercise
We first see that the ”walls” are located at 0.0cm and 6.3cm, and so, the distance spanned by 5 balls
is (6.3 − 0.0)cm = 6.3cm, and so, the diameter of one ball is 6.3
5 cm = 1.1cm.
Why is the value not 1.06cm?
In Physics, the Precision of the measurements matter! And so, when multiplying or dividing
measured quantities, we take the least significant figures when reporting our answers. In the
case above, since 6.3 has 2 significant figures, the reported answer should also have 2!
But you may ask, 5 only has one significant figure! However, this value is not ”measured” by any
device, and so we call it a ”constant” that does not contribute.
Significant figures and decimal places
1. Multiplying or dividing quantities Report the value with the least amount of significant
figures.
2. Adding or subtracting quantities Report the value with the least amount of decimal
places.
Measuring time We typically use a stopwatch to measure time.
Stopwatches are great! However, they introduce a type of error called Reaction time error, which
arises because humans have an average reaction time of 0.25s! So, the 100m sprint does not employ
people to stand at the finish time to measure the time, since there would be a delay of around 0.25s
between the runner finishing and the person pressing stop!
Figure 5: A stopwatch with hours: minutes: seconds : hundreths of a second
We can use a stopwatch to tell the time elapsed between one event and the other.
3
, Example Peter runs a 400m event, the guy measuring it forgets to set the stopwatch to 0 seconds
before starting it, and now he only has a starting time and an ending time to tell the time taken for
Peter to run
(a) How long did Peter take?
(b) What are the possible sources of error?
Figure 6: Caption
Answer:
(a) Peter took 68 seconds (or 1 minute and 8 seconds) to finish the race.
(b) Reaction time error, if we assume the reaction time to be 0.25 seconds, this creates a 0.5 swing
in the time that Peter has taken!
1.1.1 Stacking the measurements up
We first start off with a thought: Is it feasible to measure the thickness of a sheet of A4 paper using a
ruler?
Answer: Obviously not, since the thickness of a sheet of A4 paper is much less than 1mm, which is
the smallest increment that can be measured by a ruler!
So what can we do? One way to do this is to stack up 500 pieces of A4 paper together, measure the
thickness of the stack, and divide the value by 500 to get the thickness of 1 sheet!
When do we stack measurements?
Stacking up measurements is a good practice for measurements that are either too small to be
individually measured or measuring only 1 reading generates a huge error
Example An unknown stack of A4 paper has a thickness of 1 cm, what can you do to measure the
thickness of one individual sheet?
We can first carefully count the number of A4 sheets of paper and let the number be n, and so, letting
the thickness of one sheet be s
1
s=
n
For example, if n = 100, then s = 0.01cm
Units
Always include units in your measurements! And also you can check whether or not your answer
makes sense by making sure that the units are consistent throughout the equation, this is what
we call dimensional analysis, and we wll further explore it as we move on
Another application of stacking up measurements is in measuring the period of a pendulum,
which is a mass attached at the end of a string that swings under gravity!
4
Peter Nui
June 3, 2026
Contents
1 Motion, Forces and Energy 2
1.1 Making Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 Stacking the measurements up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Scalars and vectors (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.1 Distance and displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Summary of quantities with their units . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Adding vectors together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 Vectors that are at right angles with each other . . . . . . . . . . . . . . . . . . . . 10
1.4 Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 Speed and velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.3 Motion graphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.4.4 Mass and weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.4.5 Motion in free-fall without air resistance . . . . . . . . . . . . . . . . . . . . . . . . 23
1.4.6 Falling with air resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.5 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.5.1 What is density? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.5.2 Measuring density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.5.3 Floating and sinking (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.6 Effects of forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.6.1 Effects of forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.6.2 Newton’s first law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1.6.3 Newton’s second law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.6.4 Newton’s third law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.6.5 Circular motion (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.6.6 Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.6.7 Moments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.6.8 Centre of gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.7 Momentum (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
1.7.1 Impulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
1.8 Energy, work and power (Calculation are for extended only) . . . . . . . . . . . . . . . . . 47
1.8.1 Brief introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
1.8.2 Kinetic energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
1.8.3 Gravitational potential energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
1.8.4 Conservation of energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
1.8.5 Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
1.8.6 Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
1.8.7 Efficiency (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
1.9 Energy sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
1.9.1 Energy from the Sun (Extended only) . . . . . . . . . . . . . . . . . . . . . . . . . 55
1.9.2 Energy from fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
1.9.3 Energy from water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
1.9.4 Geothermal power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
1.9.5 Nuclear fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
1.10 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
1
,1 Motion, Forces and Energy
1.1 Making Measurements
What are we measuring?
In Physics, there are three quantities that you are measuring: Mass, length and time, other
important quantities include volume, current, etc.
Measuring length We typically use a ruler to measure length and volume. Rulers can typically
measure the size of objects in units of mm or cm.
Other equipment that we can use include trundle wheel and a tape measure, which can be used
to measure longer distances, typically in metres!
Figure 1: Ruler
Figure 2: Tape measure
Figure 3: Trundle wheel
However, not all of them are suitable for measuring every object! For example, it would not be
suitable to measure the height of someone using a ruler, nor is it suitable to use a trundle wheel to
measure the size of a rice grain!
2
,Example Refer to the diagram below, calculate the diameter of the circle
Figure 4: Worked Exercise
We first see that the ”walls” are located at 0.0cm and 6.3cm, and so, the distance spanned by 5 balls
is (6.3 − 0.0)cm = 6.3cm, and so, the diameter of one ball is 6.3
5 cm = 1.1cm.
Why is the value not 1.06cm?
In Physics, the Precision of the measurements matter! And so, when multiplying or dividing
measured quantities, we take the least significant figures when reporting our answers. In the
case above, since 6.3 has 2 significant figures, the reported answer should also have 2!
But you may ask, 5 only has one significant figure! However, this value is not ”measured” by any
device, and so we call it a ”constant” that does not contribute.
Significant figures and decimal places
1. Multiplying or dividing quantities Report the value with the least amount of significant
figures.
2. Adding or subtracting quantities Report the value with the least amount of decimal
places.
Measuring time We typically use a stopwatch to measure time.
Stopwatches are great! However, they introduce a type of error called Reaction time error, which
arises because humans have an average reaction time of 0.25s! So, the 100m sprint does not employ
people to stand at the finish time to measure the time, since there would be a delay of around 0.25s
between the runner finishing and the person pressing stop!
Figure 5: A stopwatch with hours: minutes: seconds : hundreths of a second
We can use a stopwatch to tell the time elapsed between one event and the other.
3
, Example Peter runs a 400m event, the guy measuring it forgets to set the stopwatch to 0 seconds
before starting it, and now he only has a starting time and an ending time to tell the time taken for
Peter to run
(a) How long did Peter take?
(b) What are the possible sources of error?
Figure 6: Caption
Answer:
(a) Peter took 68 seconds (or 1 minute and 8 seconds) to finish the race.
(b) Reaction time error, if we assume the reaction time to be 0.25 seconds, this creates a 0.5 swing
in the time that Peter has taken!
1.1.1 Stacking the measurements up
We first start off with a thought: Is it feasible to measure the thickness of a sheet of A4 paper using a
ruler?
Answer: Obviously not, since the thickness of a sheet of A4 paper is much less than 1mm, which is
the smallest increment that can be measured by a ruler!
So what can we do? One way to do this is to stack up 500 pieces of A4 paper together, measure the
thickness of the stack, and divide the value by 500 to get the thickness of 1 sheet!
When do we stack measurements?
Stacking up measurements is a good practice for measurements that are either too small to be
individually measured or measuring only 1 reading generates a huge error
Example An unknown stack of A4 paper has a thickness of 1 cm, what can you do to measure the
thickness of one individual sheet?
We can first carefully count the number of A4 sheets of paper and let the number be n, and so, letting
the thickness of one sheet be s
1
s=
n
For example, if n = 100, then s = 0.01cm
Units
Always include units in your measurements! And also you can check whether or not your answer
makes sense by making sure that the units are consistent throughout the equation, this is what
we call dimensional analysis, and we wll further explore it as we move on
Another application of stacking up measurements is in measuring the period of a pendulum,
which is a mass attached at the end of a string that swings under gravity!
4
