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Balanced, or Not

A 55-minute Grade 3 lesson on investigating what balanced and unbalanced forces do to the motion of an object.

Balanced, or Not is a free 55-minute Grade 3 science lesson plan for Common Core standard 3-PS2-1 — show what balanced and unbalanced forces do to how something moves. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.

Grade:
Grade 3
Length:
55 minutes
Standard:
3-PS2-1

Grade 3 · Physical Science

3-PS2-1

Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.

Objective

Students will be able to predict whether an object moves from the sizes of the forces on it.

Students are successful when they can

  • Reads both forces before predicting.
  • Says whether they are balanced.
  • Links balanced forces to unchanged motion.

What you need

  • Two spring scales, a box, a smooth floor
  • A results table with both pulls and the outcome
  • The printable practice sheet linked at the end of this plan

The lesson

Warm-up

5 min
  1. Two pupils pull a box with equal force and it does not move.
  2. Ask whether that means no forces are acting.

Teach — equal is not the same as none

14 min
  1. Pull the box 4 units each way. It stays still. Record both numbers.
  2. Ask what would happen if there were truly no forces. Also still — so stillness alone tells you nothing.
  3. Pull 6 left and 4 right. It moves left. Record it.
  4. Name the words: balanced means equal and opposite; unbalanced means one wins.
  5. Say what balanced forces do to motion: leave it unchanged, whether still or moving.
  6. Take a rolling ball slowing down and ask which force is unbalanced there.
“Both numbers first. Now, balanced or not?”

Investigate — six pulls

19 min
  1. Pairs pull a box with two scales, recording both readings and what happened.
  2. They do at least two balanced trials and four unbalanced.
  3. They mark every trial where the box did not move.
  4. They write the rule they found in one sentence.

Independent practice

14 min
  1. Students complete the 'Balanced, or Not' page.
  2. Check answers quote both forces, not one.

Close

3 min
  1. Ask for something in the room with balanced forces on it right now.

What goes wrong, and why

Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.

Thinks a still object has no forces on it.

Why: Nothing is happening.

Fix: A book on a table has gravity and the table pushing back. Still means balanced.

Thinks balanced forces always mean stopped.

Why: Every balanced example was still.

Fix: A sledge pushed at steady speed against equal friction keeps moving.

Reads one force and predicts.

Why: One number seems enough.

Fix: Both numbers, every time. One tells you nothing about the balance.

If they are not there yet

  • Two trials, balanced and unbalanced.
  • A table with the first row filled.

If they finish early

  • Find the smallest unbalance that moves the box.
  • Predict, then test, three pulls at once.
  • Explain why a parachute falls at a steady speed.

Exit ticket

Two teams pull a rope 5 units each way. What happens, and why?

What to look for: It does not move, because the forces are balanced. 'No forces' means the balanced idea needs another run.

Printable practice for 3-PS2-1

Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.

Questions about Balanced, or Not

How long does the Balanced, or Not lesson take?

55 minutes, split across 5 timed sections: warm-up 5 min, teach 14 min, investigate 19 min, independent practice 14 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.

Which standard does Balanced, or Not teach?

3-PS2-1 — 3-PS2-1, Physical Science for Grade 3: “Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object.” In plain terms, show what balanced and unbalanced forces do to how something moves.

What do I need to teach this lesson?

Two spring scales, a box, a smooth floor, a results table with both pulls and the outcome and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.

What mistakes should I expect in this lesson?

Three, each a reasoning error rather than carelessness: thinks a still object has no forces on it; thinks balanced forces always mean stopped and reads one force and predicts. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.

How do I know whether the lesson worked?

The exit ticket asks: “Two teams pull a rope 5 units each way. What happens, and why?.” It does not move, because the forces are balanced. 'No forces' means the balanced idea needs another run. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.

Is there a worksheet to go with Balanced, or Not?

Yes — 1 printable 3-PS2-1 worksheet, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.

Is Balanced, or Not free to use?

Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 8 September 2026. Please do not resell it or republish it as your own.

Last reviewed 2026-09-08. Aligned to 3-PS2-1 of the Next Generation Science Standards.