Year 7 Technology · 2026
Week 2 · Lesson 03

Forces Lab — 5 force types (PBS interactive) + compression/tension

Week 2 · 75 minutes · Year 7 Technology (Mandatory) · Bridge It

TE4-MSC-01TE4-PDP-01

🎯 Learning intentions

  • I can name the 5 force types (squeezing, stretching, bending, sliding, twisting) and their technical names (compression, tension, bending, shear, torsion).
  • I can complete the PBS Forces Lab interactive and fill in Workbook Q5.
  • I can predict where a paper beam will bend before I test it.

✅ Success criteria

  • My Workbook Q5 forces chart has all 5 force types filled in with technical names + effect descriptions.
  • I have completed the paper beam deflection experiment with my partner.
  • I can explain why the TOP of a loaded beam compresses and the BOTTOM stretches.

Do Now · 5 min

From Term 1 L05 — quick recall:

📝 Workbook zone

  1. Compression is a ___ force (one word).
  2. Tension is a ___ force (one word).
  3. Name one place in your body right now where compression acts.
  4. Name one place where tension acts.

I Do · ~10 min Teacher demonstration

Today we use the PBS Building Big Forces Lab — an interactive that shows 5 different forces acting on materials. Ms Gao opens it on the projector.

🔗 Forces Lab: pbs.org/wgbh/buildingbig/lab/forces

Together we observe each of the 5 forces:

Everyday nameTechnical nameWhat it does
SqueezingCompressionPushes material together, making it shorter/thicker
StretchingTensionPulls material apart, making it longer/thinner
BendingBendingTop compresses, bottom stretches — combo force
SlidingShearOne part slides past another (think of scissors)
TwistingTorsionRotates/twists a material around its long axis

Then — teacher demo of the paper beam under load:

  1. A single A4 paper flat across two chairs (the "beam"). Add a book. Watch it collapse.
  2. Fold the same paper lengthwise (concertina shape). Repeat. Watch it hold.

Why the concertina works: folds give the paper DEPTH. The top of the beam compresses slightly; the bottom stretches slightly. The more depth, the less bending. This is why real beams are I-shaped — depth without weight.

New words today:
bending = when a beam curves under load
deflection = how much a beam sags in the middle
shear = when two parts of a structure try to slide past each other

We Do · ~15 min Guided practice

Together, we draw a beam bridge with a truck on top. Mark:

  1. Where is compression? (Hint: the TOP half of the beam.)
  2. Where is tension? (The BOTTOM half of the beam.)
  3. Where is the biggest bending force? (Middle of the span.)

Now a truss bridge. The truss turns the bending of a beam into straight compression and tension in each member — that's why trusses carry more load for the same weight.

You Do · ~35 min Independent pair work

Part 1 — Workbook Q5 Forces Lab (10 min): open the PBS Forces Lab on your laptop and complete the forces chart in your workbook. 5 rows: Squeezing · Stretching · Bending · Sliding · Twisting → fill in the technical name + 1-sentence effect.

Part 2 — Mini-build #2 — Paper Beam Deflection Experiment (20 min): in pairs. You have 5 sheets of A4 paper, 30 cm masking tape, a ruler, and a 200 g weight (or a book).

  1. Test 1 — single flat sheet across 20 cm gap. Add weight to centre. Measure deflection (mm). Record.
  2. Test 2 — fold one sheet concertina-style. Repeat. Record.
  3. Test 3 — roll one sheet into a tube. Repeat. Record.
  4. Test 4 — stack 3 flat sheets. Repeat. Record.

In your workbook table: record deflection in mm for each test. Then in 2 sentences — which shape had the LEAST deflection? Why? (Hint: use the words compression, tension, bending.)

Differentiation

🪜Support

Pre-printed results table in workbook. Pair with Core student. Focus on Tests 1 + 2 only. Forces Lab read-aloud by teacher.

🎯Core

All 4 tests with table and 2-sentence reflection. Forces chart self-completed.

🚀Extension

Add Test 5 — fold paper into a tube AND add a diagonal brace. Predict AND test whether deflection decreases further. Add a 6th row to the forces chart — 'compound bending' and explain using Sweller's cognitive load principle.

Exit Ticket · 5 min

On a sticky note OR in workbook exit ticket box:

  1. Match: "Sliding" → technical name is ___.
  2. Finish this sentence: "The deeper a beam, the ___ it bends."
  3. Name ONE force from today you want to see in a real bridge this weekend.

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