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# Does a moving thing need a push?

Year 10 Physics · Newton's laws

<!-- Speaker note: Students state Newton's first law and explain why a moving object with no net force continues at constant velocity, confronting the Aristotelian idea that motion needs a continuous force (AC9S10U05, node 2, a hinge node). About 25 minutes (Engage and Explore 8 min · Explain 9 min · Evaluate 3 min · Typical adds 4 min, Wider about 3 min). -->

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## Today

**We are learning to** newton's first law: an object at rest stays at rest, and a moving object keeps moving at a constant velocity, unless a net force acts. Moving things slow down because of friction, not because their push runs out.

- I can state Newton's first law.
- I can explain why a moving object with no net force keeps a constant velocity.
- I can identify friction as the hidden force that slows everyday objects.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it does not replace air tracks or a puck on a smooth floor. Set the width with `?width=minimum`, `typical` (default) or `wider`. The Aristotelian view survives exposure to the correct definition unless it is confronted. The Explore board is that confrontation: commit to a prediction, then watch the puck coast. Board notes: motion is left and right only; friction is a fixed 2 N while sliding. Teacher: In your own words: the reply to 'the force is still in it' is the evidence. -->

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## Why it matters

> Kick a ball on grass and it rolls to a stop. Slide a puck on ice and it goes much further. In space, a probe launched decades ago is still coasting out of the solar system with its engines off.

<!-- Speaker note: For 2000 years people believed, with Aristotle, that motion needs a force to keep it going. This lesson tests that idea. -->

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<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

**A hockey stick hits a puck, then stops touching it. The puck slides across perfectly smooth ice (no friction). What do you predict happens?**

- It stops straight away
- It speeds up
- It slows down as the force of the hit runs out
- It keeps sliding at the same speed

<!-- Speaker note: What happens: It keeps sliding at the same speed. With no net force, nothing changes its motion. The 'force of the hit' isn't stored inside it: the force only acted while the stick touched it. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: ask students who chose 'slows down' to say where the force of the hit is stored. Keep their answers for Evaluate. -->

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<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%2Ffirst-law%2Fstep-2&code=widget%3A+forces%0Aobject%3A+Puck%0Amass%3A+1%0Aforce+P%3A+right%2C+4%2C+Push%2C+adjust+0-10%0Afriction%3A+2%2C+toggle%0Amotion%3A+on%0Atrack%3A+40%0Atime%3A+10%0A&fresh=1}}

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

<!-- Speaker note: Press **Play** to push the puck. After a second or two, slide **Push** to 0 and turn **Friction** off. Watch the graph and the dots. -->

<!-- Speaker note: Teacher: the check needs push 0 and friction off while moving. If a student turns friction off first, the puck speeds up: ask why. -->

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<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?

* It keeps sliding at the same speed. With no net force, nothing changes its motion. The 'force of the hit' isn't stored inside it: the force only acted while the stick touched it.

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

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<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>

## Coasting

**With no push and no friction, what did the puck do?**

- Slowed down gradually
- Stopped
- Kept moving at a constant speed

* Answer: Kept moving at a constant speed

<!-- Speaker note: No net force, no change in motion: Newton's first law. -->

<!-- Speaker note: Teacher: the 'why does a ball stop' question is where the hidden force gets named. -->

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<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>

## The law

**Which statement is Newton's first law?**

- Heavier objects are harder to keep moving
- Every object eventually comes to rest
- A moving object needs a force to keep it moving
- An object stays at rest or keeps moving at a constant velocity unless a net force acts on it

* Answer: An object stays at rest or keeps moving at a constant velocity unless a net force acts on it

<!-- Speaker note:  -->

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<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>

## Why things slow down

**So why does a ball rolling on grass slow down and stop?**

- Balls naturally stop
- Friction and air resistance act against it: a net force backwards
- Gravity pulls it backwards
- Its force runs out

* Answer: Friction and air resistance act against it: a net force backwards

<!-- Speaker note: The 'hidden' forces, friction and air resistance, are the net force that slows it. -->

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<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>

## Inertia

**What is inertia?**

- The friction on a moving object
- An object's tendency to resist changes in its motion (more mass, more inertia)
- A force that keeps objects moving

* Answer: An object's tendency to resist changes in its motion (more mass, more inertia)

<!-- Speaker note:  -->

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<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: friction is the hidden force

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

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

<!-- Speaker note: What this step is for: Running the same puck with friction on shows the everyday slowing as a net force effect, completing the replacement of the Aristotelian model. -->

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<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 slows it

**Friction is 2 N and the puck's mass is 1 kg. While it slides, what is happening?**

- A net force of 2 N backwards makes it slow down steadily
- Its push slowly runs out
- Friction is balanced by its motion

* Answer: A net force of 2 N backwards makes it slow down steadily

<!-- Speaker note: The only horizontal force is friction, so it is the net force. The graph slopes down in a straight line: steady slowing. -->

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<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: seatbelts

**A car hits a barrier and stops suddenly. A passenger isn't wearing a seatbelt. Using the first law, what happens to them?**

- They stop with the car
- They keep moving forward at the car's old speed until something (the dashboard, windscreen) exerts a force on them
- They are thrown forward by a force from the crash

* Answer: They keep moving forward at the car's old speed until something (the dashboard, windscreen) exerts a force on them

<!-- Speaker note: A seatbelt applies the force that stops the passenger along with the car, spread over a little more time and a wide area. What this step is for: The unrestrained passenger is the first law in a high-stakes setting: the car is stopped by a force; the passenger isn't. -->

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## Evaluate: look back

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

**Revision summary**

- **Newton's first law:** an object stays at rest, or keeps moving at a constant velocity, unless a **net force** acts on it.
- A moving object does **not** need a force to keep moving. A force is needed to **change** motion.
- Everyday objects slow down because of **friction and air resistance**: hidden forces that are the net force.
- **Inertia** is an object's resistance to changes in its motion; more mass, more inertia.

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<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 spacecraft coasts through empty space with its engines off. Describe its motion and explain.**

* It keeps moving at a constant velocity: there is no net force (no friction or air resistance), so by the first law its motion doesn't change.

<!-- 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: acceleration as a defined quantity (node 3), then F = ma (node 4). In class: a puck or dry-ice block on a smooth bench; a coin on a card flicked off a cup (inertia). -->