كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

Theme A — Space, Time and Motion

A.1 Kinematics — IB Physics HL Revision Notes & Topical Questions

5 min read 9 parts Lesson 2 of 63 1 quiz

📚 IB Physics HL Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

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Lesson summary

A.1 Kinematics — IB PHYSICS HL notes: Describe motion in one and two dimensions using displacement, velocity and acceleration, the equations of uniformly accelerated motion, projectile motion and drag.Distance = how far an object travels in total — a scalar.Displacement = the cha…

Instantaneous velocity
Positive acceleration means speeding up in the positive direction
Uniform acceleration is constant
They apply to constant acceleration in a straight line
What the symbols mean
Choose a positive direction and keep to it

Part 1 of 7Distance, displacement, speed and velocity

Distance

Distance how far an object travels in total — a scalar.

Displacement

Displacement the change in position, with direction — a vector.

A runner completing a 400 m lap has distance 400 m but displacement zero.

Speed

Speed distance per unit time — a scalar, in m s^-1.

Average speed = total distance / time taken.

Velocity

Velocity the rate of change of displacement — a vector that can be negative.

Average velocity = total displacement / total time.
For constant acceleration, average velocity = (u + v)/2.

Instantaneous velocity

Instantaneous velocity the velocity at one moment — the gradient of the tangent to a displacement–time graph.

Part 2 of 7Acceleration

Acceleration

Acceleration the rate of change of velocity — a vector in m s^-2.

a = Δv / Δt, where Δv = v − u.

An object accelerates whenever its velocity changes in size or direction.

Positive acceleration means speeding up in the positive direction

Positive acceleration means speeding up in the positive direction negative acceleration (deceleration) means slowing down or speeding up in the negative direction.

Instantaneous acceleration is the gradient of the tangent to a velocity–time graph.

Uniform acceleration is constant

Uniform acceleration is constant e.g. free fall; non-uniform acceleration changes.

Part 3 of 7Motion graphs

Graph	Gradient	Area under graph	Straight line means
Displacement–time	Velocity	Meaningless	Constant velocity
Velocity–time	Acceleration	Change in displacement	Uniform acceleration
Acceleration–time	Meaningless	Change in velocity	Constant acceleration

Displacement–time: a curve means acceleration, a positive slope is motion in the positive direction and a horizontal line is rest.

Velocity–time: a horizontal line is constant velocity and a curve is non-uniform acceleration.

Areas below the time axis count as negative.

Bouncing ball (upwards positive).

At the top the velocity is momentarily zero and changes sign, while the acceleration g stays downward.
At the bottom the velocity reverses sign instantly with the same speed, giving a large momentary acceleration.

Part 4 of 7Kinematic (suvat) equations

1They apply to constant acceleration in a straight line

They apply to constant acceleration in a straight line and relate s, u, v, a and t.

v u + at

What the symbols mean: v = final velocity (m s⁻¹) · u = initial velocity (m s⁻¹) · a = acceleration (m s⁻²) · t = time (s)

s ut + ½at²

What the symbols mean: s = displacement (m) · u = initial velocity (m s⁻¹) · a = acceleration (m s⁻²) · t = time (s)

4v2

v2 u² + 2as

What the symbols mean: v = final velocity · u = initial velocity (m s⁻¹) · a = acceleration (m s⁻²) · s = displacement (m)

½(u + v)t

What the symbols mean: s = displacement (m) · u = initial velocity · v = final velocity (m s⁻¹) · t = time (s); (u + v)/2 is the average velocity

Key phrases.

"Starts from rest" means u = 0.
"Falling due to gravity" means a = g = 9.8 m s^-2.

7Choose a positive direction and keep to it

Choose a positive direction and keep to it all vectors (s, u, v, a) must use the same convention.

Method.

List the known and unknown variables with signs.
Choose the equation that contains them.
Convert to SI units, substitute and rearrange.

Part 5 of 7Projectile motion

Projectile motion

Projectile

Projectile a particle moving freely under gravity in a two-dimensional plane — with fluid resistance negligible and g constant.

Resolve the launch velocity u at angle θ

Resolve the launch velocity u at angle θ horizontal u cos θ and vertical u sin θ.

Horizontal and vertical motion are independent

Horizontal and vertical motion are independent only time is shared.

Quantity	Horizontal	Vertical
Velocity	Constant (u cos θ)	Changes; zero at maximum height
Acceleration	Zero	g = 9.8 m s^-2 downward
Displacement	Range at the end of the flight	Maximum height at half the flight time

Time of flight

Time of flight the total time in the air; maximum height at half of it for level ground.

Range

Range horizontal distance travelled; the path is a symmetrical parabola without air resistance.

Cases include horizontal projection and projection above or below the horizontal.

Part 6 of 7Fluid resistance and terminal speed

Fluid resistance and terminal speed

Fluid resistance (viscous drag)

Fluid resistance (viscous drag) a frictional force from a gas or liquid on a moving body.

It acts opposite to the motion, never speeds an object up and transfers energy away to the surroundings.
It increases with the speed of the object.

Lift

Lift an upward force perpendicular to the flow, from air pushed down — Newton's third law.

Effect on a projectile.

Horizontal velocity, time of flight, range and maximum height all decrease.
Horizontal deceleration increases and the path is no longer a parabola — steeper on the way down.

Terminal speed.

A falling body accelerates and drag increases with speed.
The resultant force and acceleration decrease.
When drag equals weight, acceleration is zero and the speed is constant.

A heavier body has a higher terminal speed

A heavier body has a higher terminal speed opening a parachute lowers it as the skydiver decelerates to a new terminal speed.

Part 7 of 7More from the specification

Kinematics equations

Kinematics equations for constant acceleration, final velocity equals initial velocity plus acceleration times time,
and displacement follows from the other suvat equations

Velocity-time graph

Velocity-time graph the gradient represents acceleration and the area under it represents displacement

Terminal speed

Terminal speed drag increases with speed until it equals the weight, so the resultant force and acceleration become zero

Cyclist

Cyclist a cyclist reaches terminal velocity when driving force equals resistive force, and the graph flattens

Velocity-time graph

A graph of velocity against time whose gradient is acceleration and area is displacement.

Key terms

Term	Meaning
Displacement	Change in position, with direction.
Velocity	Rate of change of displacement.
Acceleration	Rate of change of velocity.
Instantaneous value	Value at one moment, from a tangent gradient.
Projectile	Object moving freely under gravity after launch.
Terminal speed	Constant speed when drag equals weight.
Uniform acceleration	Acceleration constant in magnitude and direction.

Avoid these mistakes

Mixing signs of s, u, v and a — pick one positive direction for all.

Using suvat equations when acceleration is not constant.

Giving distance instead of displacement — direction matters for a vector.

Treating negative acceleration as always meaning slowing down.

Using horizontal and vertical quantities in the same equation — separate the components.

Last updated: 18 October 2026

Physics 0625 & 9702 SUVAT Mastery Graph Interpretation

Constant Acceleration Equations (SUVAT) & Slopes

v = u + at | s = ut + ½at² | v² = u² + 2as | s = ½(u + v)t

Displacement-Time Graph: Gradient = Velocity (curve = accelerating).
Velocity-Time Graph: Gradient = Acceleration; Area under curve = Distance travelled / Displacement.
Free Fall in vacuum: a = g ≈ 9.81 m/s² downwards (air resistance negligible).