Teacher sheet · Ages 15–16 · about 45–50 minutes
Bone tissue and bones as levers
Lesson page: echoesof.science/school/skeleton/ages-15-16/ · Pupil worksheet: echoesof.science/school/skeleton/ages-15-16/print/
Learning aims
- Relate the structure of compact and spongy bone and of the bone matrix to function.
- Describe bone remodelling and growth at the epiphyseal plate.
- Apply the principle of moments to the forearm lever.
- Plan, carry out and evaluate a lever investigation with uncertainties.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: hold a heavy book with your arm bent at 90°. Feel your biceps. Guess the muscle force. |
| 10 min | Read the text; bone tissue and remodelling. |
| 20 min | Model-forearm practical. |
| 5 min | Worked example: 470 N. |
| 5 min | Quiz or calculator game. |
Materials for the experiment
- A 50 cm wooden ruler (the forearm)
- A clamp stand with a pivot or a nail/hinge through one end of the ruler (the elbow)
- A 0–10 N newton meter (the biceps)
- String loops
- 100 g masses with a hanger
- Safety glasses
Safety: Wear safety glasses in case a string or the newton meter springs loose. Keep feet and hands clear under the hanging masses and do not exceed the newton meter's range. Clamp the stand firmly to the bench.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| A muscle only needs to pull as hard as the load. | Because it attaches close to the joint, it must pull several times harder (about 7.4 × in the example). |
| Adult bone never changes. | It is remodelled all the time by osteoblasts and osteoclasts. |
| Bone is just mineral, like rock. | It is a composite: collagen gives flexibility and hydroxyapatite gives hardness. |
Worksheet answers
- Compact: dense, osteons, outer wall, resists compression. Spongy: lattice of trabeculae along stress lines, lighter, holds red marrow in some bones.
- Weights: 2.50 × 9.80 = 24.5 N; 4.00 × 9.80 = 39.2 N. F × 0.0400 = 24.5 × 0.160 + 39.2 × 0.380 = 3.92 + 14.9 = 18.8 N m, so F = 18.8 / 0.0400 ≈ 470 N.
- Values should lie close to a straight line through the origin; uncertainties include the newton meter resolution (for example ±0.1 N), judging when the ruler is level and measuring d; use a spirit level, a finer meter and repeat readings.
- Bone contains living cells and is constantly rebuilt: osteoblasts form new bone, osteocytes maintain it and osteoclasts break it down; it also has blood vessels and nerves in its canals.
Quiz answers
- Which cells break down bone? Osteoclasts. Osteoclasts resorb bone; osteoblasts form it.[4]
- What gives bone its flexibility? Collagen fibres. Collagen stops bone being brittle; hydroxyapatite gives hardness.[4]
- Trabeculae in spongy bone form… along lines of stress. They line up along lines of stress to strengthen the bone.[4]
- Load 20 N at 30 cm from the elbow, muscle attached at 3 cm (forearm weight ignored). The muscle force is… 200 N. F = 20 × 30 / 3 = 200 N.[7]
- What remains when a long bone stops growing in length? The epiphyseal line. The growth plate is replaced and only the epiphyseal line remains.[5]
- How many bones does the adult skeleton usually have? 206. 206 named bones: 80 axial and 126 appendicular.[1]
Going further
Calculate the force in the elbow joint in the textbook example (answer: about 407 N). Why is the joint force so large?
Sources used in this lesson
- [1] Divisions of the Skeleton (SEER Training Modules, National Cancer Institute (NIH, USA)): reliability High
- [2] Anatomy and Physiology 2e, 6.1 The Functions of the Skeletal System (OpenStax, Rice University): reliability High
- [3] Anatomy and Physiology 2e, 6.2 Bone Classification (OpenStax, Rice University): reliability High
- [4] Anatomy and Physiology 2e, 6.3 Bone Structure (OpenStax, Rice University): reliability High
- [5] Anatomy and Physiology 2e, 6.4 Bone Formation and Development (OpenStax, Rice University): reliability High
- [6] Kids and Their Bones: A Guide for Parents (National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIH, USA)): reliability High
- [7] College Physics 2e, 9.6 Forces and Torques in Muscles and Joints (OpenStax, Rice University): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/skeleton/sources/
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