MYP Physics

F.1 Speed and Acceleration

Motion is one of the most fundamental ideas in physics. In this unit, you will investigate how objects move, represent motion using graphs, and use equations to predict future motion. These concepts provide the foundation for mechanics in both MYP and IGCSE Physics.

Questions to explore

? How can we describe and predict the motion of objects around us?
? What information can graphs reveal that calculations alone cannot?
? How can equations help us predict future motion?
? Why is acceleration more than simply speeding up?

💡 Key ideas, explained simply

🚶 Speed vs velocity

Speed tells you how fast — it is a *scalar* (just a number with a unit, like $5\text{ m/s}$ ).

Velocity tells you how fast and in which direction — it is a *vector*. Walking $5\text{ m/s}$ north and $5\text{ m/s}$ south are the same speed but opposite velocities. If a question says "velocity", always give a direction.

📈 What acceleration really means

Acceleration is how quickly velocity changes each second, measured in $\text{m/s}^2$ . A car going from $0$ to $20\text{ m/s}$ in $4\text{ s}$ speeds up by $5\text{ m/s}$ every second — an acceleration of $5\text{ m/s}^2$ .

Slowing down is negative acceleration (deceleration). Turning a corner at steady speed is *also* acceleration, because the direction of velocity changes.

The two graphs MYP loves: on a distance–time graph the gradient is speed; on a velocity–time graph the gradient is acceleration and the area underneath is distance.

📖 Key terms

Scalar: A quantity with size only, e.g. distance, speed, time.
Vector: A quantity with size and direction, e.g. displacement, velocity.
Displacement: Straight-line distance and direction from start to finish.
Average speed: Total distance ÷ total time, $v = \frac{d}{t}$ .
Acceleration: Rate of change of velocity, $a = \frac{v-u}{t}$ , in $\text{m/s}^2$ .
Uniform motion: Moving at constant velocity — zero acceleration, a straight line on a d–t graph.

1 Key Formulas

Average Speed

v = \frac{d}{t}

Acceleration

a = \frac{v-u}{t}

SUVAT Equation

v=u+at

SUVAT Equation

s=ut+\frac{1}{2}at^2

SUVAT Equation

s=\frac{(u+v)}{2}t

✏️ Worked example

Calculate acceleration

A cyclist speeds up from $4\text{ m/s}$ to $16\text{ m/s}$ in $6\text{ s}$ . Find the acceleration.

1

Write the formula

$a = \dfrac{v - u}{t}$
2

List the values

Final velocity $v = 16\text{ m/s}$ , initial $u = 4\text{ m/s}$ , time $t = 6\text{ s}$ .
3

Substitute

$a = \dfrac{16 - 4}{6} = \dfrac{12}{6}$

✓

a = 2 m/s² — the cyclist gains 2 m/s of speed every second.

🏎️ Physics around you

Car adverts boast "0 to 100 km/h in 3 seconds" — that is an acceleration claim. A high number means the velocity changes very fast, which is why you feel pushed back into the seat. Your phone measures acceleration too: that is how it knows when you rotate it.

🎯 Nail it in the exam

Distance-Time and Velocity-Time Graphs

Graphs are one of the most frequently assessed topics in MYP and IGCSE Physics.

Distance-Time Graphs

- Gradient = Speed.

- Horizontal line = Stationary object.

- Straight sloping line = Constant speed.

- Curved line = Changing speed.

- Steeper line = Greater speed.

Velocity-Time Graphs

- Gradient = Acceleration.

- Horizontal line = Constant velocity.

- Positive gradient = Positive acceleration.

- Negative gradient = Deceleration.

- Area under the graph = Displacement.

Students should be able to interpret graphs, sketch graphs from descriptions, and describe motion using appropriate scientific vocabulary.

Pro Exam Strategy

Always check the graph axes before answering.
Distance-time graphs show speed from the gradient.
Velocity-time graphs show acceleration from the gradient.
Area under a velocity-time graph gives displacement.
Use a ruler when sketching graphs.

Constant Acceleration and SUVAT

Many MYP 5 and introductory IGCSE questions involve motion with constant acceleration.

Students should confidently solve one-step and two-step numerical problems using:

$v=u+at$

$s=ut+\frac12at^2$

$s=\frac{(u+v)}{2}t$

Focus on identifying the known quantities before selecting the appropriate equation. Always write the formula first, substitute the values with units, and then calculate the final answer.

Pro Exam Strategy

Write down the known quantities (u, v, a, t, s).
Choose the equation containing only one unknown.
Always include units in the final answer.
Check whether acceleration is positive or negative.
Convert km/h to m/s before solving if required.

Common Past Paper Pitfalls

Many students lose marks because they confuse speed with velocity or use the wrong graph interpretation.

Remember:

- Speed is scalar.

- Velocity includes direction.

- Gradient of distance-time graph = speed.

- Gradient of velocity-time graph = acceleration.

- Area under velocity-time graph = displacement.

Pro Exam Strategy

Horizontal line on a distance-time graph means stationary.
Horizontal line on a velocity-time graph means constant velocity.
A steeper distance-time graph means greater speed.
Always state units for gradient and area calculations.
Show every step of your working.

🧠 Check your understanding

Tap an answer to see if you're right — and why.

Q1. A cyclist travels 120 m in 24 s. What is the average speed?

$2\,m/s$
$4\,m/s$
$5\,m/s$
$6\,m/s$

Q2. A car accelerates uniformly from 10 m/s to 22 m/s in 6 s. What is its acceleration?

$1\,m/s^2$
$2\,m/s^2$
$3\,m/s^2$
$4\,m/s^2$

📝 Exam-style questions

Try each one, then reveal the model answer.

F.1 Speed and Acceleration

Questions to explore

💡 Key ideas, explained simply

🚶 Speed vs velocity

📈 What acceleration really means

📖 Key terms

1 Key Formulas

✏️ Worked example

🏎️ Physics around you

🎯 Nail it in the exam

Distance-Time and Velocity-Time Graphs

Constant Acceleration and SUVAT

Common Past Paper Pitfalls

🧠 Check your understanding

📝 Exam-style questions

Want Speed and Acceleration explained properly?

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