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# Same push, different mass

Year 7 Physics · Forces and motion

<!-- Speaker note: Students state the qualitative relationship between force, mass and acceleration, predict which object accelerates more under the same force, and read the pattern from data (AC9S7U04, node 5, an integration node). About 17 minutes (Engage and Explore 6 min · Explain 8 min · Evaluate 3 min · Typical adds 3 min, Wider about 1 min). -->

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## Today

**We are learning to** for the same unbalanced force, a heavier object accelerates less than a lighter one. For the same mass, a bigger unbalanced force gives a bigger acceleration. Data from a force investigation show the pattern: acceleration goes up with force and down with mass.

- I can say what happens to acceleration when the force or the mass changes.
- I can predict which of two objects accelerates more under the same force.
- I can read a pattern from force data.

<!-- Speaker note: Before class: A short integration tutorial that follows the four Year 7 forces lessons. Set the width with `?width=minimum`, `typical` (default) or `wider`. The Year 10 lessons put numbers on this (F = ma); here the aim is the qualitative pattern and the data. Board notes: the trolley sits on a frictionless track; the board shows the acceleration before Play. The data tables in the questions are small, rounded numbers chosen for a clear pattern. Don't call the pattern F = ma yet. Teacher: In your own words: the two bar graphs and a sentence for each. -->

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## Why it matters

> A rugby front-rower and a winger sprint off the same line with the same push from the ground. Who gets going faster, and why?

<!-- Speaker note: You know that an unbalanced force changes motion. This lesson puts force, mass and acceleration together. -->

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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

**You give an empty trolley and a full trolley exactly the same steady push. Which one speeds up more?**

- They speed up equally
- The empty one: a smaller mass accelerates more for the same force
- The full one: it has more mass to push
- Neither: a steady push only gives a steady speed

<!-- Speaker note: What happens: The empty one. For the same unbalanced force, a bigger mass means a smaller acceleration. Mass resists changes in motion. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. Ask the 'full one' group what a heavier trolley resists. -->

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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-7%2Fforce-mass%2Fstep-2&code=widget%3A+forces%0Aobject%3A+Trolley%0Amass%3A+1%2C+10%2C+2%0Aforce+P%3A+right%2C+6%2C+Push%0Amotion%3A+on%0Atrack%3A+40%0Atime%3A+4%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-7/force-mass/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask what happened to the acceleration when the mass doubled. -->

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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?

* The empty one. For the same unbalanced force, a bigger mass means a smaller acceleration. Mass resists changes in motion.

<!-- 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>

## Which accelerates more

**The same unbalanced force acts on a 2 kg object and an 8 kg object. Which accelerates more?**

- The 2 kg object
- The 8 kg object
- Both the same

* Answer: The 2 kg object

<!-- Speaker note: For the same force, the smaller mass accelerates more. -->

<!-- Speaker note: Teacher: the two statements and the data patterns are the success criteria. -->

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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 relationship

**Which statement is right?**

- A bigger mass gives a bigger acceleration
- A bigger unbalanced force gives a bigger acceleration, and a bigger mass gives a smaller one
- Force and mass don't affect acceleration

* Answer: A bigger unbalanced force gives a bigger acceleration, and a bigger mass gives a smaller one

<!-- Speaker note: More force, more acceleration. More mass, less acceleration. -->

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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>

## Force data

**Same trolley, 2 kg. Pushing with 2 N gives 1 m/s², 4 N gives 2 m/s², 6 N gives 3 m/s². What acceleration would 10 N give (m/s²)?**

* Answer: 5

<!-- Speaker note: The acceleration goes up by the same amount for each extra newton: 10 N gives 5 m/s². -->

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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>

## Mass data

**Same push of 8 N. A 1 kg trolley accelerates at 8 m/s², 2 kg at 4 m/s², 4 kg at 2 m/s². What acceleration would 8 kg give (m/s²)?**

* Answer: 1

<!-- Speaker note: Each time the mass doubles, the acceleration halves: 8 kg gives 1 m/s². -->

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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>

## Mix it up

**Looking back at unbalanced forces: a box slides to the right. Friction pulls it left with 6 N and nothing pushes it. What does the box do?**

- It keeps sliding at a steady speed
- It speeds up to the right
- It slows down
- It stops straight away

* Answer: It slows down

<!-- Speaker note: The net force is 6 N to the left, against the motion, so the box slows down. What this step is for: Acceleration needs an unbalanced force, so the effect of a net force on motion comes back before force and mass are compared. -->

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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: hit a target

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-7%2Fforce-mass%2Fstep-5&code=widget%3A+forces%0Aobject%3A+Trolley%0Amass%3A+1%2C+10%2C+5%0Aforce+P%3A+right%2C+6%2C+Push%2C+adjust+0-20%0Amotion%3A+on%0Atrack%3A+40%0Atime%3A+4%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-7/force-mass/?full=step-5#step-5)

<!-- Speaker note: What this step is for: Choosing the force to hit a target acceleration for a given mass uses the pattern in reverse. -->

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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>

## Double the mass

**You change the mass to 10 kg and keep the same push. What must happen to the acceleration?**

- It doubles
- It stays the same
- It halves

* Answer: It halves

<!-- Speaker note: Doubling the mass halves the acceleration for the same push. -->

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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: rockets and roads

**A rocket burns fuel, so its mass falls while the thrust stays the same. What happens to its acceleration?**

- It increases
- It stays the same
- It decreases

* Answer: It increases

<!-- Speaker note: The same force on a smaller mass gives a bigger acceleration. This is one reason rockets are built in stages that fall away. What this step is for: Engineers use the same pattern: to accelerate faster, raise the force or cut the mass. -->

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## Evaluate: look back

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

**Revision summary**

- For the **same unbalanced force**, a **larger mass** gives a **smaller acceleration**.
- For the **same mass**, a **larger unbalanced force** gives a **larger acceleration**.
- Data show the pattern: acceleration rises with force and falls as mass rises.

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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

**The same push is given to a 3 kg box and a 6 kg box. Which accelerates more, and by how much compared with the other?**

* The 3 kg box. It accelerates twice as much, because it has half the mass.

<!-- 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: Year 8 energy, then Year 10 Newton's laws, where the pattern becomes F = ma. In class: a dynamics trolley on a ramp with a light string and different masses; a bowling ball and a tennis ball given the same push; data logging with light gates if available. -->