1. More information on joints!

2. But first…
What would happen if you put a disc down on top of this glass of water (that fits exactly)?

3. But first…
This disc could not be pushed down any further, because water is a non-compressible fluid. This means that we cannot lower the volume of this water.

4. But first…
What if the glass is filled with a gas? Could you push this disc down?

5. But first…
Yes, because gases are compressible fluids.

6. But first…
Hydraulic machines work based on the fact that water is non-compressible.

7. But first…
The joints in your body also have a non-compressible fluid that works in the same way. This is called synovial fluid.

8. Remember…
A synovial joint is where 2 bones are linked together, allowing them to move.
They contain a space (called a sinus) that is filled with synovial fluid (non-compressible).
The fluid allows a force or constraint to be transmitted without having the bones rub against one another.

9. Bones Summary
Bones support the body, and act as levers to move the body.
They are light and strong.
Properties: Hardness
Resilience Tensile Strength (not elastic)

10. Muscles contract to move the joint.
Muscle Summary
Muscles contract to move the joint.
Properties: High elasticity
Tensile strength (in some)

11. Tendons link muscles to bone.
They hold and stabilize the joint and help in its movement.
Properties: High tensile strength Low elasticity
Flexible

12. Ligaments link bones to bones. They support and stabilize the joint.
Properties: High tensile strength
No elasticity (like rope)
Flexible

13. Cartilage protects the ends of bones. It reduces friction
Synovial Cartilage
Cartilage protects the ends of bones.
It reduces friction
Properties: Resilient
Hard
Smooth and slippery

14. Synovial fluid reduces shock. It lubricates the joint.
It protects tendons and ligaments.
Properties: Non-compressible fluid
Very low friction
Works like hydraulics