What do the Grade 9 Physics cards cover?

37 cards across 7 chapters of the national textbook: Physics and Human Society, Physical Quantities, Motion in a Straight Line, Force, Work, Energy and Power, Simple Machines, Mechanical Oscillation and Sound and Temperature and Thermometry. You can take any chapter one card at a time on the page itself.

Is there a national exam in Grade 9?

No. Ethiopia sets national exams in Grade 6, Grade 8 and Grade 12 only. These cards are for your school's own exams, and for the national exam that comes a few years later.

Where do these cards come from?

They are drafted from Grade 9 Physics, the Ministry of Education textbook for this grade. A second pass that cannot see the chapter then re-derives every formula, constant and table row, and anything it cannot confirm is held back instead of published.

Yes. Every card here is free to read and the printable sheet is free to download. Neither needs an account.

When was this last checked?

6 September 2026. Cards arrive chapter by chapter, and the line under each one says when that card was last read through.

Free short notes and revision cards

Grade 9 Physics

Grade 9 Physics on Temari has 37 revision cards, arranged by the chapters of the Ethiopian national curriculum. Every card says when the rule applies, what each symbol in it stands for, and the mistake students most often make with it. They are free to read and need no account.

37
Cards: 7
Chapters: 19
Formulas: 11
Reference tables: Grade 9 Physics
Textbook: Free
Price: 6 September 2026
Last checked

Everything37Formula17Reference table11Common mistake5Rule4

Physics and Human Society

Branches of PhysicsReference tableMechanics · Acoustics · Optics · +4

Branch	Subject of Study
Mechanics	Motion of objects with or without forces
Acoustics	Sound, its production, transmission, and effects
Optics	Behavior and properties of light
Thermodynamics	Heat, thermal energy, and heat transfer
Electromagnetism	Electric and magnetic fields and forces
Nuclear physics	Structure, properties, and reactions of atomic nuclei
Astrophysics	Astronomical objects and celestial phenomena

When you use it

Use this to classify physical phenomena into their correct subfields of physics.

Watch out

Do not confuse mechanics with thermodynamics. Mechanics deals with motion and forces, whereas thermodynamics deals strictly with heat and temperature transfer.

Drafted from Grade 9 Physics, pages 2-11, then checked twice before it went up

Classical and Modern PhysicsRule

When you use it

Use this to distinguish historical eras and conceptual shifts in physics development.

Watch out

Classical physics covers discoveries from the Renaissance up to the end of the 19th century. Developments starting at the beginning of the 20th century belong to modern physics.

Drafted from Grade 9 Physics, pages 2-11, then checked twice before it went up

Prominent PhysicistsReference tableGalileo Galilei · Isaac Newton · Michael Faraday · +3

Scientist	Key Contribution
Galileo Galilei	Telescopic astronomy and the scientific method
Isaac Newton	Laws of motion and universal gravitation
Michael Faraday	Electromagnetic induction and electrolysis
James Prescott Joule	Mechanical equivalent of heat and conservation of energy
Marie Curie	Radioactivity, polonium, and radium
Albert Einstein	Theory of relativity and quantum theory

When you use it

Use this to identify major historical scientists and the fundamental principles they discovered.

Watch out

James Prescott Joule linked heat to mechanical work. Faraday is the contributor for electromagnetic induction, not Joule.

Drafted from Grade 9 Physics, pages 2-11, then checked twice before it went up

Physical Quantities

Metric Unit PrefixesReference tabletera · giga · mega · +6

Prefix	Symbol	Factor
tera	T	$10^{12}$
giga	G	$10^9$
mega	M	$10^6$
kilo	k	$10^3$
centi	c	$10^{-2}$
milli	m	$10^{-3}$
micro	$\mu$	$10^{-6}$
nano	n	$10^{-9}$
pico	p	$10^{-12}$

When you use it

Use when converting very large or very small measurements into standard powers of 10.

Watch out

Micro uses the Greek letter $\mu$ for $10^{-6}$ , while milli uses m for $10^{-3}$ . Do not confuse the symbols.

Drafted from Grade 9 Physics, pages 12-35, then checked twice before it went up

Scalars and VectorsRule

When you use it

Use to classify physical quantities based on whether direction is required along with magnitude.

Watch out

Distance and speed are scalars, but displacement and velocity are vectors. Mass is a scalar, whereas force is a vector.

Drafted from Grade 9 Physics, pages 12-35, then checked twice before it went up

Seven Fundamental SI QuantitiesReference tableLength · Mass · Time · +4

Physical quantity	Symbol	SI Unit	Unit Symbol
Length	$l$	meter	m
Mass	$m$	kilogram	kg
Time	$t$	second	s
Temperature	$T$	kelvin	K
Current	$I$	ampere	A
Amount of substance	$n$	mole	mol
Luminous intensity	$I_v$	candela	cd

When you use it

Use this reference to identify the seven base physical quantities and their standard SI units.

Watch out

Speed, force, and density are derived quantities. Only these seven cannot be defined in terms of other quantities.

Drafted from Grade 9 Physics, pages 12-35, then checked twice before it went up

Zero Point in Temperature ScalesCommon mistake

When you use it

Use when identifying valid mathematical operations on interval and ratio measurement scales.

Watch out

Celsius and Fahrenheit are interval scales without a true zero, so values cannot be multiplied or divided. Only the Kelvin scale is a ratio scale with an absolute zero.

Drafted from Grade 9 Physics, pages 12-35, then checked twice before it went up

Motion in a Straight Line

Average AccelerationFormula

\vec{a}_{av} = \frac{\vec{v}_f - \vec{v}_i}{t_f - t_i} = \frac{\Delta \vec{v}}{\Delta t}

\vec{a}_{av} = \frac{\vec{v}_f - \vec{v}_i}{t_f - t_i} = \frac{\Delta \vec{v}}{\Delta t}

$\vec{a}_{av}$: average acceleration $m\,s^{-2}$
$\vec{v}_f$: final velocity $m\,s^{-1}$
$\vec{v}_i$: initial velocity $m\,s^{-1}$
$\Delta \vec{v}$: change in velocity $m\,s^{-1}$
$\Delta t$: time interval $s$

When you use it

Use to calculate the rate of change of velocity over a given time interval.

Watch out

When an object slows down, final velocity is less than initial velocity, resulting in negative acceleration (deceleration).

Drafted from Grade 9 Physics, pages 36-59, then checked twice before it went up

Average SpeedFormula

v_{av} = \frac{s_{tot}}{t_{tot}}

v_{av} = \frac{s_{tot}}{t_{tot}}

$v_{av}$: average speed $m\,s^{-1}$
$s_{tot}$: total distance $m$
$t_{tot}$: total time $s$

When you use it

Use to calculate the rate at which total distance is covered over the total time taken.

Watch out

Always convert non SI units before calculating. Multiply km/h by 10/36 to convert to m/s.

Drafted from Grade 9 Physics, pages 36-59, then checked twice before it went up

Average VelocityFormula

\vec{v}_{av} = \frac{\Delta \vec{S}}{\Delta t} = \frac{\vec{S}_f - \vec{S}_i}{t_f - t_i}

\vec{v}_{av} = \frac{\Delta \vec{S}}{\Delta t} = \frac{\vec{S}_f - \vec{S}_i}{t_f - t_i}

$\vec{v}_{av}$: average velocity $m\,s^{-1}$
$\Delta \vec{S}$: displacement $m$
$\vec{S}_f$: final position $m$
$\vec{S}_i$: initial position $m$
$\Delta t$: time interval $s$
$t_f$: final time $s$
$t_i$: initial time $s$

When you use it

Use to calculate the rate of change of position in a specific direction over a time interval.

Watch out

Displacement depends on initial and final positions only. It is not the total distance travelled along the path.

Drafted from Grade 9 Physics, pages 36-59, then checked twice before it went up

Motion Graphs InterpretationReference tableS-t · v-t

Graph	Slope	Area Under Curve
$S-t$	velocity	No physical meaning
$v-t$	acceleration	distance or displacement

When you use it

Use when finding velocity, acceleration, or distance from position-time and velocity-time graphs.

Watch out

The slope of a v-t graph gives acceleration, while the area under it gives distance or displacement. Do not mix slope and area.

Drafted from Grade 9 Physics, pages 36-59, then checked twice before it went up

Round Trip DisplacementCommon mistake

When you use it

Reach for this when an object completes a trip and returns to its starting point.

Watch out

When an object returns to its starting point, net displacement is zero and average velocity is zero, but total distance and average speed are greater than zero.

Drafted from Grade 9 Physics, pages 36-59, then checked twice before it went up

Force, Work, Energy and Power

Gravitational Potential EnergyFormula

E_p = m g h

E_p = m g h

$E_p$: gravitational potential energy $\text{J}$
$m$: mass $\text{kg}$
$g$: acceleration due to gravity $\text{m}\,\text{s}^{-2}$
$h$: height $\text{m}$

When you use it

Use to find the stored energy of an object raised to a height above the ground.

Watch out

Height h is the vertical distance above the reference point, not the path length along a slope.

Drafted from Grade 9 Physics, pages 60-81, then checked twice before it went up

Kinetic EnergyFormula

E_k = \frac{1}{2} m v^2

E_k = \frac{1}{2} m v^2

$E_k$: kinetic energy $\text{J}$
$m$: mass $\text{kg}$
$v$: speed $\text{m}\,\text{s}^{-1}$

When you use it

Use to calculate the energy possessed by an object due to its motion.

Watch out

Square only the speed v, not the mass. Doubling the speed quadruples the kinetic energy.

Drafted from Grade 9 Physics, pages 60-81, then checked twice before it went up

Newton's Second LawFormula

F = m a

F = m a

$F$: net force $\text{N}$
$m$: mass $\text{kg}$
$a$: acceleration $\text{m}\,\text{s}^{-2}$

When you use it

Use when calculating acceleration, net force, or mass of an accelerating body.

Watch out

Mass must always be converted to kg before calculating. Unbalanced force produces acceleration, not constant velocity.

Drafted from Grade 9 Physics, pages 60-81, then checked twice before it went up

PowerFormula

P = \frac{W}{t}

P = \frac{W}{t}

$P$: power $\text{W}$
$W$: work done or energy transferred $\text{J}$
$t$: time taken $\text{s}$

When you use it

Use to calculate the rate at which work is done or energy is transferred.

Watch out

Time t must be converted to seconds before dividing. One watt is one joule per second.

Drafted from Grade 9 Physics, pages 60-81, then checked twice before it went up

Work DoneFormula

W = F_{\parallel} S

W = F_{\parallel} S

$W$: work $\text{J}$
$F_{\parallel}$: force in direction of displacement $\text{N}$
$S$: displacement $\text{m}$

When you use it

Use when a constant force moves an object through a displacement parallel to the force.

Watch out

Carrying an object horizontally does no work against gravity because force and displacement are perpendicular.

Drafted from Grade 9 Physics, pages 60-81, then checked twice before it went up

Simple Machines

Machine Efficiency, Mechanical Advantage and Velocity RatioFormula

\eta = \frac{\text{MA}}{\text{VR}} = \frac{\text{Work output}}{\text{Work input}}

\eta = \frac{\text{MA}}{\text{VR}} = \frac{\text{Work output}}{\text{Work input}}

$\eta$: Efficiency of the machine $\text{dimensionless}$
$\text{MA}$: Mechanical Advantage, ratio of Load to Effort $\text{dimensionless}$
$\text{VR}$: Velocity Ratio, distance moved by Effort over distance moved by Load $\text{dimensionless}$
$\text{Work output}$: Useful work done by the machine on the Load $\text{J}$
$\text{Work input}$: Work put into the machine by the Effort $\text{J}$

When you use it

Use when finding the efficiency of any simple machine or relating output work and input work to mechanical advantage and velocity ratio.

Watch out

Mechanical Advantage, Velocity Ratio, and Efficiency are ratios and have no units. Efficiency is always less than 1 (or less than 100 percent) in real machines.

Drafted from Grade 9 Physics, pages 82-113, then checked twice before it went up

Machines Do Not Multiply Energy or WorkCommon mistake

When you use it

Use when evaluating true or false statements and conceptual questions about whether machines create energy or decrease total work.

Watch out

Machines never multiply work or energy. A machine can multiply force or multiply speed and distance, but never both at the same time. Due to friction, work output is always less than work input, so AMA is always less than IMA.

Drafted from Grade 9 Physics, pages 82-113, then checked twice before it went up

Three Classes of LeversReference table1st Class · 2nd Class · 3rd Class

Class	Middle Component	IMA Characteristic	Examples
1st Class	Fulcrum	$\text{IMA} > 1$ , $\text{IMA} = 1$ , or $\text{IMA} < 1$	Seesaw, scissors, crowbar
2nd Class	Load	$\text{IMA} > 1$	Wheelbarrow, nutcracker, bottle opener
3rd Class	Effort	$\text{IMA} < 1$	Tweezers, broom, fishing pole, tongs

When you use it

Use to identify the class of a lever based on which point lies in the middle: Fulcrum, Load, or Effort.

Watch out

Remember the middle component order: 1st class has Fulcrum in the middle, 2nd class has Load in the middle, and 3rd class has Effort in the middle.

Drafted from Grade 9 Physics, pages 82-113, then checked twice before it went up

Velocity Ratio and IMA of Simple MachinesReference tableInclined Plane · Wedge · Screw · +2

Simple Machine	Velocity Ratio (VR) Formula	Symbols
Inclined Plane	$\text{VR} = \frac{l}{h}$	$l = \text{slope length},\; h = \text{height}$
Wedge	$\text{VR} = \frac{l}{t}$	$l = \text{penetration length},\; t = \text{thickness}$
Screw	$\text{IMA} = \frac{2\pi r}{p} = \frac{\pi d}{p}$	$r = \text{radius},\; d = \text{diameter},\; p = \text{pitch}$
Wheel and Axle	$\text{VR} = \frac{R}{r}$	$R = \text{wheel radius},\; r = \text{axle radius}$
Pulley System	$\text{VR} = N$	$N = \text{number of rope strands supporting load}$

When you use it

Use to calculate the theoretical Velocity Ratio or Ideal Mechanical Advantage directly from the physical dimensions of the machine.

Watch out

For a screw, pitch is the distance between consecutive threads. For wheel and axle, ensure the effort radius is divided by the load radius.

Drafted from Grade 9 Physics, pages 82-113, then checked twice before it went up

Mechanical Oscillation and Sound

Echo and Sonar DistanceCommon mistake

When you use it

Apply when solving problems where sound travels to an obstacle and reflects back to the observer or source.

Watch out

The measured time t is for the round trip. The one way distance to the obstacle is d = v times t / 2. Forgetting to divide by 2 gives double the actual distance.

Drafted from Grade 9 Physics, pages 114-139, then checked twice before it went up

Period of a Mass Spring SystemFormula

T = 2\pi \sqrt{\frac{m}{k}}

T = 2\pi \sqrt{\frac{m}{k}}

$T$: Period $s$
$m$: Mass $kg$
$k$: Spring constant $N\,m^{-1}$

When you use it

Use this formula to calculate the period of oscillation for a mass attached to a horizontal or vertical spring.

Watch out

Mass must be in kilograms and spring constant k in N/m. The period depends only on mass and spring constant, not on displacement amplitude.

Drafted from Grade 9 Physics, pages 114-139, then checked twice before it went up

Period of a Simple PendulumFormula

T = 2\pi \sqrt{\frac{L}{g}}

T = 2\pi \sqrt{\frac{L}{g}}

$T$: Period $s$
$L$: Length of pendulum $m$
$g$: Acceleration due to gravity $m\,s^{-2}$

When you use it

Use this formula to find the period of a simple pendulum or to calculate local gravitational acceleration from pendulum length and period.

Watch out

The mass of the bob and the amplitude do not affect the period. Length must be converted from centimeters to meters.

Drafted from Grade 9 Physics, pages 114-139, then checked twice before it went up

Speed of Sound in AirFormula

v = 331 \sqrt{1 + \frac{T_c}{273}}

v = 331 \sqrt{1 + \frac{T_c}{273}}

$v$: Speed of sound $m\,s^{-1}$
$T_c$: Air temperature $^\circ\text{C}$

When you use it

Use this formula to find the speed of sound in air at any given Celsius temperature.

Watch out

Insert the temperature directly in degrees Celsius, not Kelvin. The speed of sound at 0 degrees Celsius is 331 m/s.

Drafted from Grade 9 Physics, pages 114-139, then checked twice before it went up

Wave Speed EquationFormula

v = f \lambda

v = f \lambda

$v$: Wave speed $m\,s^{-1}$
$f$: Frequency $Hz$
$\lambda$: Wavelength $m$

When you use it

Use this formula to relate the propagation speed of any periodic wave to its frequency and wavelength.

Watch out

Wavelength must be in meters. If given the period T instead of frequency, use f = 1/T.

Drafted from Grade 9 Physics, pages 114-139, then checked twice before it went up

Transverse and longitudinal wavesReference tableHow the particles move · What the diagram shows · The parts you label · +2

What to compare	Transverse wave	Longitudinal wave
How the particles move	At right angles to the direction the wave travels.	Back and forth along the same line the wave travels.
What the diagram shows	A sine curve of crests and troughs, with the travel arrow drawn along the horizontal axis.	A band of vertical lines that are alternately crowded and spread out, labelled C R C R C, with the travel arrow drawn along the band.
The parts you label	Crests at the top of the curve and troughs at the bottom.	Compressions, marked C, where the particles are crowded and the pressure is high; rarefactions, marked R, where they are spread apart and the pressure is low.
Examples	Water waves, where the surface moves up and down while the wave travels across it. Light.	Sound in air, sent out as a vibrating object pushes and pulls the air beside it.
What actually travels	The energy goes forward. Each particle only swings about its own resting place.	The energy goes forward. Each particle only swings about its own resting place.

When you use it

Use when a question asks which kind a given wave is, or asks you to label a wave diagram. Compare two directions: the way the particles of the medium vibrate and the way the wave itself travels. At right angles means transverse, along the same line means longitudinal.

Watch out

Students memorise the picture instead of the motion, so they see sound drawn as a smooth curve on an oscilloscope and answer that sound is transverse. That curve is a graph of displacement or pressure against distance or time. It is not a picture of what the air is doing. In air the particles move back and forth along the very line the sound is travelling, so sound stays longitudinal however it is graphed. Judge by the direction the particles vibrate and never by the shape of the drawing.

Mechanical and electromagnetic wavesReference tableA medium to travel through · What moves it along · Speed · +4

What to compare	Mechanical wave	Electromagnetic wave
A medium to travel through	Needed. It must have a solid, a liquid or a gas.	Not needed. It carries itself across empty space, which is how starlight reaches us, and it can still pass through glass or water.
What moves it along	Each particle of the medium pushes and pulls the next one.	An oscillating electric field and magnetic field that keep regenerating each other.
Speed	The medium sets it. Sound in air at room temperature is about 340 m/s.	Every one of them travels at about 300 000 000 m/s in a vacuum.
Transverse or longitudinal	Either. A wave on a string is transverse and sound in air is longitudinal.	Always transverse.
Examples	Sound, water waves, a wave on a stretched string, seismic waves.	Light, radio waves, X-rays. Radio, television and mobile signals all travel this way.
In medical imaging	Ultrasound scanning, which is sound above 20 kHz.	X-ray imaging.
The test that settles it	Ring an alarm clock inside a jar and pump the air out. The sound fades to nothing.	The light from that same clock still reaches your eye.

When you use it

Use when a question asks which waves can cross a vacuum, or gives you a list of waves to sort into two groups. One thing decides every case: a mechanical wave needs matter to travel through and an electromagnetic wave does not.

Watch out

Students see X-ray and ultrasound printed together under medical imaging and file both as electromagnetic. Ultrasound is sound. It is a mechanical wave that needs tissue to travel through, and that is exactly why the technician squeezes gel between the probe and the skin: a thin layer of air would reflect the sound back and the scan would show nothing. X-rays need no medium at all. The exam question that catches this is always the same one, asking which of the listed waves can travel through a vacuum. Light, radio and X-rays can. Sound, ultrasound, water waves and seismic waves cannot.

Nodes and antinodes in a standing waveRule

\text{node to node} = \dfrac{\lambda}{2}, \; \text{node to antinode} = \dfrac{\lambda}{4}

\text{node to node} = \dfrac{\lambda}{2}, \; \text{node to antinode} = \dfrac{\lambda}{4}

$\lambda$: the wavelength of each of the two travelling waves that build the pattern $\mathrm{m}$
$A$: the amplitude of one of those two waves on its own $\mathrm{m}$
$2A$: the amplitude at an antinode, twice that of a single wave $\mathrm{m}$

When you use it

Use for a string, a rope or an air column vibrating in a fixed pattern, where a node stays still at all times and an antinode swings twice as far as either wave alone. Node to node is half a wavelength and node to antinode is a quarter, which is what turns a measured length into a wavelength.

Watch out

Students take the distance between two neighbouring nodes to be one full wavelength. It is half of one. That single slip breaks every string and pipe question: a string of length L vibrating in its fundamental holds one loop, so L is half a wavelength, the wavelength is twice L, and the frequency comes out as the wave speed divided by twice L. Read the wavelength as L instead and the answer is double the true frequency every time. Count loops rather than nodes, because each loop between two nodes is half a wave. One more thing to be exact about: an antinode has the largest amplitude of swing, and its displacement still passes through zero twice every cycle, at the instants when the whole medium is momentarily straight.

Constructive and destructive interferenceRule

A_{res} = A_{1} + A_{2} \text{ or } A_{res} = |A_{1} - A_{2}|

A_{res} = A_{1} + A_{2} \text{ or } A_{res} = |A_{1} - A_{2}|

$A_{1}$: the amplitude of the first wave $\mathrm{m}$
$A_{2}$: the amplitude of the second wave $\mathrm{m}$
$A_{res}$: the resultant amplitude where the two overlap: the sum when they arrive in phase, the difference when they arrive half a cycle apart $\mathrm{m}$

When you use it

Use when two waves overlap at a point and a question asks how loud, how bright or how tall the result is. Add the amplitudes when the waves arrive in phase, which means a path difference of a whole number of wavelengths, and subtract them when the waves arrive half a cycle apart, which means a path difference of an odd number of half wavelengths.

Watch out

Students read destructive as the waves being destroyed and expect silence or darkness whenever two waves meet out of step. Two things have to be true before the result is zero: the waves must arrive exactly half a cycle apart, which is an odd number of half wavelengths of path difference rather than merely out of step, and their amplitudes must be equal. A 3 cm wave meeting a 2 cm wave in antiphase leaves a 1 cm wave. Nothing is lost either. The energy taken from the quiet points reappears at the loud ones, and both waves come out of the meeting exactly as they went in.

Energy carried by a mechanical waveFormula

E \propto A^{2} f^{2}

E \propto A^{2} f^{2}

$E$: the energy the wave carries. It travels forward while the particles of the medium only swing about their resting places $\mathrm{J}$
$A$: the displacement amplitude: how far each particle swings from its resting place $\mathrm{m}$
$f$: the frequency of the wave, the number of complete oscillations each second $\mathrm{Hz}$

When you use it

Use when a question changes the amplitude or the frequency of a sound, a wave on a string or a water wave and asks what happens to the energy it carries. Both quantities are squared, so doubling either one on its own gives four times the energy and doubling both gives sixteen times.

Watch out

Students read the proportion as a straight multiplication and say that doubling the amplitude doubles the energy. It quadruples, because the amplitude is squared, and doubling the amplitude and the frequency together gives sixteen times the energy rather than four. The second trap is hearing higher frequency as louder: a higher frequency sound is higher in pitch, and loudness is what the amplitude controls. Note also that the relation carries no constant, so it compares two waves of the same kind in the same medium and never gives an energy in joules. It belongs to mechanical waves alone and does not carry over to light, whose brightness is set by amplitude while frequency changes the colour.

Temperature and Thermometry

Fixed Points of Temperature ScalesReference tableCelsius · Fahrenheit · Kelvin

Scale	Ice Point	Steam Point	Divisions
Celsius	$0^\circ\text{C}$	$100^\circ\text{C}$	$100$
Fahrenheit	$32^\circ\text{F}$	$212^\circ\text{F}$	$180$
Kelvin	$273.15\text{ K}$	$373.15\text{ K}$	$100$

When you use it

Reference the standard calibration fixed points and division counts across standard scales.

Watch out

A temperature difference of 1 degree Celsius is equal to 1 Kelvin, but it is not equal to 1 degree Fahrenheit.

Drafted from Grade 9 Physics, page 140 onwards, then checked twice before it went up

Linear Thermal ExpansionFormula

\Delta L = \alpha L_0 \Delta T

\Delta L = \alpha L_0 \Delta T

$\Delta L$: change in length $\text{m}$
$\alpha$: coefficient of linear expansion $(^\circ\text{C})^{-1}$
$L_0$: initial length $\text{m}$
$\Delta T$: change in temperature $^\circ\text{C}$

When you use it

Calculate the expansion or contraction in length of a solid rod when its temperature changes.

Watch out

Do not confuse the change in length with the final length. The final length is the initial length plus the change in length.

Drafted from Grade 9 Physics, page 140 onwards, then checked twice before it went up

Temperature Scale ConversionFormula

T_C = \frac{5}{9}(T_F - 32) = T_K - 273.15

T_C = \frac{5}{9}(T_F - 32) = T_K - 273.15

$T_C$: temperature in Celsius $^\circ\text{C}$
$T_F$: temperature in Fahrenheit $^\circ\text{F}$
$T_K$: temperature in Kelvin $\text{K}$

When you use it

Convert temperature readings between Celsius, Fahrenheit, and Kelvin scales.

Watch out

Subtract 32 before multiplying by 5/9 when converting Fahrenheit to Celsius. Do not use degree signs with Kelvin.

Drafted from Grade 9 Physics, page 140 onwards, then checked twice before it went up

Thermal Expansion of Holes and CavitiesCommon mistake

When you use it

Use when determining whether a hole or inner diameter expands or contracts during heating.

Watch out

A hole in an object does not shrink when heated. It expands at the exact same rate as if it were filled with solid material.

Drafted from Grade 9 Physics, page 140 onwards, then checked twice before it went up

Thermometers and Thermometric PropertiesReference tableMercury thermometer · Alcohol thermometer · Resistance thermometer · +1

Thermometer	Thermometric Property	Measuring Range
Mercury thermometer	Length of mercury column	$-30^\circ\text{C}\text{ to }300^\circ\text{C}$
Alcohol thermometer	Expansion of alcohol volume	$-115^\circ\text{C}\text{ to }78.15^\circ\text{C}$
Resistance thermometer	Electrical resistance of platinum	$-270^\circ\text{C}\text{ to }700^\circ\text{C}$
Thermocouple	Voltage between two junctions	$-270^\circ\text{C}\text{ to }2300^\circ\text{C}$

When you use it

Select appropriate thermometer types and identify their physical thermometric properties.

Watch out

Alcohol thermometers are chosen for very cold environments because alcohol freezes at a much lower temperature than mercury.

Drafted from Grade 9 Physics, page 140 onwards, then checked twice before it went up

Specific heat capacity and latent heatFormula

Q = mc\,\Delta T \text{ and } Q = mL

Q = mc\,\Delta T \text{ and } Q = mL

$Q$: the heat energy transferred because of a temperature difference. A body does not contain heat; it contains internal energy, and heat is that energy while it is moving $\mathrm{J}$
$m$: the mass of the substance being heated, cooled or changed $\mathrm{kg}$
$c$: the specific heat capacity of the material: the energy that raises 1 kg of it by 1 K. For water it is about 4200 J per kilogram per kelvin $\mathrm{J\,kg^{-1}\,K^{-1}}$
$\Delta T$: the change in temperature. A Celsius interval and a kelvin interval are the same size, so the number is the same either way $\mathrm{K}$
$L$: the specific latent heat: fusion for melting and freezing, vaporisation for boiling and condensing. For water these are about 334 000 and about 2 260 000 joules per kilogram $\mathrm{J\,kg^{-1}}$
$C$: the heat capacity of one whole body, which is its mass times c. A big block has a larger C than a small block of the same material $\mathrm{J\,K^{-1}}$

When you use it

Use whenever a question heats, cools, melts, freezes or boils something and asks for the energy. While the thermometer is still moving, the energy is mass times specific heat capacity times temperature change; while it holds steady at a melting or boiling point, it is mass times specific latent heat.

Watch out

Students reach for the temperature form on a melting or boiling step. Asked for the energy that turns 0.5 kg of ice at 0 °C into water at 0 °C, they look for a temperature change, find none, and either write zero or invent one. Melting has no temperature change at all: it is mass times the latent heat of fusion, which comes to 167 000 J. On a heating curve, use the temperature form on the sloping parts and the latent heat form on the flat parts, then add the steps. The other slip is swapping C for c. Capital C belongs to one particular object and is measured in J/K; small c belongs to the material and is measured in J/(kg K), and small c is the one printed in the data table.

The same subject in other years

An exam paper keeps asking for what the year below taught. Those cards are here too.

Your other Grade 9 subjects

Everything else in this year that has cards so far.

Questions students ask

What do the Grade 9 Physics cards cover?: 37 cards across 7 chapters of the national textbook: Physics and Human Society, Physical Quantities, Motion in a Straight Line, Force, Work, Energy and Power, Simple Machines, Mechanical Oscillation and Sound and Temperature and Thermometry. You can take any chapter one card at a time on the page itself.
Is there a national exam in Grade 9?: No. Ethiopia sets national exams in Grade 6, Grade 8 and Grade 12 only. These cards are for your school's own exams, and for the national exam that comes a few years later.
Where do these cards come from?: They are drafted from Grade 9 Physics, the Ministry of Education textbook for this grade. A second pass that cannot see the chapter then re-derives every formula, constant and table row, and anything it cannot confirm is held back instead of published.
Is this free?: Yes. Every card here is free to read and the printable sheet is free to download. Neither needs an account.
When was this last checked?: 6 September 2026. Cards arrive chapter by chapter, and the line under each one says when that card was last read through.

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