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# Does balanced mean no forces?

Year 7 Physics · Forces and motion

<!-- Speaker note: Students identify balanced and unbalanced forces and predict the motion, recognising that balanced forces mean no change in motion, not no forces (AC9S7U04, node 2, a hinge node). About 25 minutes (Engage and Explore 8 min · Explain 8 min · Evaluate 3 min · Typical adds 4 min, Wider about 5 min). -->

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## Today

**We are learning to** balanced forces cancel out (the net force is zero), so the motion doesn't change. The object stays still or keeps moving at a steady speed. Unbalanced forces change the motion.

- I can tell balanced from unbalanced forces in a diagram.
- I can explain that balanced forces mean no change in motion, not no forces.
- I can predict the motion from a force diagram.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it does not replace trolleys and force meters. Set the width with `?width=minimum`, `typical` (default) or `wider`. The hinge misconception is "balanced means no forces" (and its partner, "moving needs a forward force"). The Explore board has motion with balanced forces, which is exactly the case students don't expect. Board notes: the box moves left and right only. Friction is fixed at its limit while sliding and matches the push when stationary. The board starts the box at 3 m/s so students can find the steady-speed push (6 N). Teacher: In your own words: the 'balanced isn't no forces' paragraph is the evidence. -->

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## Why it matters

> A car cruises down the highway at a steady 100 km/h, engine running. Is its engine pushing harder than the air and the road are holding it back?

<!-- Speaker note: Last lesson: drawing forces. This lesson: what the diagram tells you about the motion. -->

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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 car drives along a straight road at a steady 100 km/h. Compare the forward force from the engine with the backward forces (air and road friction).**

- Forward force is bigger, or the car would stop
- They are equal: the forces are balanced
- There are no forces on it while it cruises
- Backward forces are bigger

<!-- Speaker note: What happens: They are equal. At a steady speed the forces are balanced: the net force is zero, so the motion doesn't change. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. Most will choose 'forward force is bigger'. -->

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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%2Fbalanced%2Fstep-2&code=widget%3A+forces%0Aobject%3A+Box%0Amass%3A+2%0Aforce+P%3A+right%2C+2%2C+Push%2C+adjust+0-12%0Afriction%3A+6%0Amotion%3A+on%0Aspeed%3A+3%0Atrack%3A+40%0Atime%3A+10%0A&fresh=1}}

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

<!-- Speaker note: The box starts moving at 3 m/s. Press **Play**, then try different pushes (**Reset** to start again). Watch the speed–time graph and the dots: evenly spaced dots mean a steady speed. -->

<!-- Speaker note: Teacher: if students struggle, ask them to compare the push and friction numbers when the graph is flat. -->

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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?

* They are equal. At a steady speed the forces are balanced: the net force is zero, so the motion doesn't change.

<!-- 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>

## Steady speed

**When the box moved at a steady speed, what was true?**

- There were no forces on it
- The push was bigger than friction
- The push equalled friction: balanced, net force 0

* Answer: The push equalled friction: balanced, net force 0

<!-- Speaker note: Balanced forces: equal and opposite. They are both still acting; they cancel out. -->

<!-- Speaker note: Teacher: the first question is the checkpoint; the two sorts apply 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>

## What the net force does

**What happens with each net force? (The box is already moving to the right.)**

Groups: Speeds up · Steady speed · Slows down

Push 9 N, friction 6 N · Push 6 N, friction 6 N · Push 2 N, friction 6 N · Push 12 N, friction 6 N

* Answer: Push 9 N, friction 6 N → Speeds up; Push 6 N, friction 6 N → Steady speed; Push 2 N, friction 6 N → Slows down; Push 12 N, friction 6 N → Speeds up

<!-- 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>

## Balanced or not

**Balanced or unbalanced?**

Groups: Balanced · Unbalanced

A book resting on a desk · A car cruising at a steady speed · A ball speeding up as it rolls down a slope · A skydiver falling at a steady speed · A cyclist braking · A plane taking off down the runway

* Answer: A book resting on a desk → Balanced; A car cruising at a steady speed → Balanced; A ball speeding up as it rolls down a slope → Unbalanced; A skydiver falling at a steady speed → Balanced; A cyclist braking → Unbalanced; A plane taking off down the runway → Unbalanced

<!-- 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>

## Mix it up

**Looking back at force arrows: a diagram shows a 30 N push to the right and 10 N of friction to the left. How do the arrows look?**

- The two arrows are the same length
- The push arrow is three times as long as the friction arrow, and they point opposite ways
- Both arrows point to the right
- The friction arrow is longer, because friction is stronger

* Answer: The push arrow is three times as long as the friction arrow, and they point opposite ways

<!-- Speaker note: The length of an arrow shows the size of the force, and it points the way the force acts. 30 N is three times 10 N. What this step is for: Balanced forces are equal and opposite, which only makes sense once arrow length is read as the size of the force. -->

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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: the falling skydiver

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-7%2Fbalanced%2Fstep-5&code=widget%3A+forces%0Aobject%3A+Skydiver%0Amass%3A+100%0Ag%3A+9.8%0Aforce+W%3A+down%2C+weight%2C+Weight%0Aforce+A%3A+up%2C+300%2C+Air+resistance%2C+adjust+0-1200+by+10%0A&fresh=1}}

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

<!-- Speaker note: What this step is for: A vertical case with motion (falling at a steady speed) tests whether students apply 'balanced means no change in motion' beyond the board's horizontal case. -->

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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>

## Still falling?

**Her forces are balanced. Is she still falling?**

- No, she has stopped in mid-air
- Yes, at a steady speed
- She is speeding up

* Answer: Yes, at a steady speed

<!-- Speaker note: This steady speed is her terminal velocity: weight and air resistance cancel, so her speed stays the same. -->

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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: slowing down and stopping

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-7%2Fbalanced%2Fstep-6&code=widget%3A+forces%0Aobject%3A+Box%0Amass%3A+2%0Aforce+P%3A+right%2C+6%2C+Push%2C+adjust+0-12%0Afriction%3A+6%0Amotion%3A+on%0Aspeed%3A+3%0Atrack%3A+40%0Atime%3A+10%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-7/balanced/?full=step-6#step-6)

<!-- Speaker note: What this step is for: Making the box stop with friction connects unbalanced forces to slowing down and shows what friction does once motion has stopped. -->

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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>

## Friction at rest

**Once the box has stopped, with a push of 2 N, the friction is shown as 2 N, not 6 N. Why?**

- Friction only resists as much as it needs to, up to its limit
- The board is wrong
- Friction disappears when things stop

* Answer: Friction only resists as much as it needs to, up to its limit

<!-- Speaker note: A stationary object's friction matches the push, up to a limit (6 N here). Beyond that, the object starts sliding. -->

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## Evaluate: look back

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

**Revision summary**

- **Balanced** forces are equal and opposite: the **net force is zero**. They are still acting; they cancel.
- Balanced forces mean **no change in motion**: still objects stay still; moving objects keep a steady speed in a straight line.
- **Unbalanced** forces change the motion: the object speeds up, slows down or changes direction, the way the net force points.
- A car at a steady speed has balanced forces: the engine's push equals air resistance plus friction.

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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 cyclist rides at a steady 20 km/h on a flat road. Are the forces on her balanced? Explain.**

* Yes: she isn't speeding up or slowing down, so her forward force equals the backward forces (air resistance and friction).

<!-- 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: unbalanced forces and changes in motion (node 3), then gravity (node 4). In Year 10 this becomes Newton's first law. In class: a trolley pulled by a force meter at constant speed (the meter reading equals friction); a tug of war at a standstill. -->