What it shows
Where two bones meet, a joint lets them move in a particular way. Models made from waste show how a ball and socket, a hinge, a pivot and a gliding joint each allow a different movement.
The science
A ball and socket joint, such as the shoulder and hip, lets bones move in almost every direction. A hinge joint, such as the elbow, knee and finger, bends only in one plane, like a door. A pivot joint, such as the top of the neck, lets one bone turn round another, so you can shake your head. Gliding joints, such as those between wrist bones, let bones slide past each other. Cartilage and a slippery fluid reduce friction in joints, and ligaments hold bones together.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A plastic bottle cap or small bowl and a table tennis ball or a ball of clay (ball and socket)
- Two ice-cream sticks and a split pin or paper fastener (hinge)
- A cardboard tube with a pencil or stick inside a loop (pivot)
- Two flat pieces of thick card or sandpaper-covered cardboard (gliding)
- A cardboard base and markers
- Glue, tape and scissors
Safety
For this project: An adult must cut tubes and help with the split pin. Keep small balls and pins away from young children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Glue the bottle cap onto a card as a cup, and set the ball inside it so it can turn; this is the ball and socket joint.
Join two ice-cream sticks with a split pin at one end so they swing open and shut, for the hinge.
Fix a card strip on the cardboard tube as the "bone", and loop a second card around it so it can turn but not slide off, for the pivot.
Place the two flat pieces of card touching each other on the base so they can slide along each other without falling off, for the gliding joint.
Test each joint with your hand and write the kinds of movement it allows, such as forward, backward, sideways and round.
Move your own shoulder, elbow, neck and wrist and match each real joint to a model.
Label each model with its name, an example in the body and the movement it makes.
Draw a skeleton on a chart paper and place the four models next to the matching body parts.
What you should see
Four labelled models each move in a different way: the ball turns in all directions, the hinge opens and shuts, the pivot twists and the gliding pieces slide. A chart links each one to a body part.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which joint lets the arm swing in a full circle?
The ball and socket joint at the shoulder.
2Which joint is like a door hinge?
The elbow, knee and finger joints.
3What holds bones together at a joint?
Ligaments.
4What does cartilage do in a joint?
It cushions the bone ends and reduces friction.
Take it further
Add rubber-band muscles across each model to show how muscles pull on bones to make a joint move.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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