---
marp: true
theme: default
html: true
---

# What is acceleration, exactly?

Year 10 Physics · Newton's laws

<!-- Speaker note: Students define acceleration as the rate of change of velocity, calculate it from data and graphs in m/s², and treat it as a vector in the direction of the net force (AC9S10U05, node 3, a hinge node). About 25 minutes (Engage and Explore 7 min · Explain 9 min · Evaluate 3 min · Typical adds 5 min, Wider about 2 min). -->

---

## Today

**We are learning to** acceleration is the rate of change of velocity, a = Δv ÷ Δt, in m/s². It has a direction, the same as the net force. Slowing down is acceleration too (opposite to the motion), and on a speed–time graph acceleration is the gradient.

- I can define acceleration as the rate of change of velocity, in m/s².
- I can calculate acceleration from velocity and time data, and read it from a speed–time graph.
- I can explain that acceleration has a direction, the same as the net force; slowing down is acceleration too.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it does not replace motion sensors or ticker timers. Set the width with `?width=minimum`, `typical` (default) or `wider`. The hinge is the shift from the everyday word to a defined quantity. Keep separating "fast" from "changing speed". Board notes: the board's acceleration reading appears under the board, so the number checks use different numbers from the board where possible. The slowing-down board uses friction 4 N on 2 kg: a = −2 m/s². Teacher: In your own words: the cruising-car explanation is the evidence. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 27px; }</style>

---

## Why it matters

> A Formula 1 car reaches 100 km/h in under 3 seconds. A train takes about 40. Both end up fast; one accelerates far more. Fast and accelerating are not the same thing.

<!-- Speaker note: In everyday talk "accelerate" means speed up. In physics it means something more exact. -->

---

<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**Which has the bigger acceleration: a car cruising at a steady 100 km/h, or a cyclist going from 0 to 20 km/h in 4 seconds?**

- Neither has any acceleration
- Both the same
- The cyclist, because their speed is changing
- The car, because it is much faster

<!-- Speaker note: What happens: The cyclist. The car's speed isn't changing, so its acceleration is zero, however fast it goes. Acceleration is how quickly velocity changes. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: ask why the cruising car isn't accelerating. Most will say it is. -->

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-10%2Facceleration%2Fstep-2&code=widget%3A+forces%0Aobject%3A+Trolley%0Amass%3A+2%0Aforce+P%3A+right%2C+6%2C+Push%2C+adjust+0-12%0Amotion%3A+on%0Atrack%3A+120%0Atime%3A+6%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-10/acceleration/?full=step-2#step-2)

<!-- Speaker note: Press **Play**. Watch how much the speed goes up each second (the graph and the numbers under it). -->

<!-- Speaker note: Teacher: pause at 1, 2 and 3 seconds and read the speed: +3 m/s each time. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* The cyclist. The car's speed isn't changing, so its acceleration is zero, however fast it goes. Acceleration is how quickly velocity changes.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## From the data

**The trolley went from 0 to 12 m/s in 4 s. What was its acceleration, in m/s²?**

* Answer: 3

<!-- Speaker note: a = change in velocity ÷ time = (12 − 0) ÷ 4 = 3 m/s². Its speed went up by 3 m/s every second. -->

<!-- Speaker note: Teacher: insist on units for every answer aloud. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## On the graph

**On the speed–time graph, where can you see the acceleration?**

- Where the line ends
- How high the line is
- The gradient (steepness) of the line

* Answer: The gradient (steepness) of the line

<!-- Speaker note: A steeper line means the speed changes faster: bigger acceleration. A flat line means zero acceleration. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Units

**What are the units of acceleration?**

- N
- m/s² (metres per second, per second)
- m/s
- km/h

* Answer: m/s² (metres per second, per second)

<!-- Speaker note:  -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Another one

**A cyclist goes from 2 m/s to 10 m/s in 4 s. Acceleration, in m/s²?**

* Answer: 2

<!-- Speaker note: (10 − 2) ÷ 4 = 2 m/s². -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Accelerating or not

**Is it accelerating?**

Groups: Accelerating · Not accelerating

A car cruising at a steady 100 km/h on a straight road · A bike slowing down for traffic lights · A runner rounding a bend at a steady speed · A trolley speeding up from rest · A parked car

* Answer: A car cruising at a steady 100 km/h on a straight road → Not accelerating; A bike slowing down for traffic lights → Accelerating; A runner rounding a bend at a steady speed → Accelerating; A trolley speeding up from rest → Accelerating; A parked car → Not accelerating

<!-- Speaker note:  -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 24px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Which way

**A trolley is moving to the right, and the net force on it points to the left. Which way does its acceleration point?**

- Nowhere: it has no acceleration while it still moves right
- Right, the way it is moving
- Left, the same way as the net force

* Answer: Left, the same way as the net force

<!-- Speaker note: Acceleration always points the same way as the net force. Here that is backwards, so the trolley slows down. -->

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: slowing down

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-10%2Facceleration%2Fstep-4&code=widget%3A+forces%0Aobject%3A+Trolley%0Amass%3A+2%0Aforce+P%3A+right%2C+0%2C+Push%0Afriction%3A+4%0Amotion%3A+on%0Aspeed%3A+8%0Atrack%3A+40%0Atime%3A+6%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-10/acceleration/?full=step-4#step-4)

<!-- Speaker note: What this step is for: A negative acceleration (opposite to the motion) shows acceleration as a direction, not just 'more speed'. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Negative acceleration

**It went from 8 m/s to 0 in 4 s. What was its acceleration, in m/s²? (Use a minus sign for slowing down.)**

* Answer: -2

<!-- Speaker note: (0 − 8) ÷ 4 = −2 m/s². The minus sign means the acceleration points backwards, opposite to the motion, the same way as the net force (friction). -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Direction

**Which way did the net force point while it slowed down?**

- Backwards, the same way as the acceleration
- There was no net force
- Forwards, the way it was moving

* Answer: Backwards, the same way as the acceleration

<!-- Speaker note: Acceleration always points the same way as the net force. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Elaborate: turning

**A car drives around a roundabout at a steady 30 km/h. Is it accelerating?**

- Only if it speeds up
- No: its speed is constant
- Yes: its direction is changing, so its velocity is changing

* Answer: Yes: its direction is changing, so its velocity is changing

<!-- Speaker note: There must be a net force towards the centre of the roundabout: the friction of the tyres on the road. What this step is for: A constant-speed turn is acceleration with no change of speed, the hardest case for 'acceleration = speeding up'. -->

---

## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- **Acceleration** is the rate of change of velocity: **a = Δv ÷ Δt**, in **m/s²**.
- It has a **direction**, the same as the net force. Slowing down is acceleration opposite to the motion (negative).
- A fast object at a steady speed has **zero** acceleration.
- On a speed–time graph, acceleration is the **gradient**.

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**A sprinter goes from 0 to 9 m/s in 3 s. What is her acceleration?**

* a = (9 − 0) ÷ 3 = 3 m/s², forwards.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Next: F = ma (node 4), which links the acceleration to the net force and the mass. In class: a motion sensor and a trolley on a ramp, or a ticker timer. -->