Noadswood Science, 2012

The Arm & Moments  To know the structure of the arm and to be able to work out moments Friday, August 07, 2015

Skeleton  What is the skeleton?  Why do we have one?  What makes up our skeletal system?

Skeleton  Our skeleton is made up of 206 bones: calcium and other minerals make the bone strong but slightly flexible  Bone is a living tissue with a blood supply (it can repair itself if broken, and exercise and a balanced diet are important for a healthy skeleton)  The skeleton has three main functions: -  Supporting the body  Protecting some of the vital organs  Helping the body move

Movement  Some bones in the skeleton are joined rigidly together and cannot move against each other - bones in the skull are joined like this  Other bones are joined to each other by flexible joints - muscles are needed to move bones attached by joints

Strength  The human skeleton is very strong, especially teeth…  Special support is needed if teeth are knocked out to try and make them as strong as the originals…

Skeleton  The skeleton has over 200 bones – you will need to be able to recap the bones which make up the arm…

Joints  A joint is where two or more bones meet – all synovial joints (a freely moveable joint) have the same components: -  Cartilage reduces friction acting as a shock absorber  Synovial fluid lubricates the joint  Synovial membrane produces synovial fluid  Tendons join muscle to bone enabling movement  Ligaments join bone to bone, stabilising the joint

Antagonistic Muscles  Muscles can only pull, and they work by getting shorter (contract)  As muscles can only pull, each joint is moved by a pair of muscles - an antagonistic pair  Muscles are attached to bones by strong tendons - when a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint

Antagonistic Muscles  The elbow joint lets our forearm move up or down, controlled by two muscles, the biceps on the front of the upper arm, and the triceps on the back of the upper arm: -  When the biceps muscle contracts, the forearm moves up  When the triceps muscle contracts, the forearm moves down Forearm up Biceps contract (triceps relaxed) Forearm down Triceps contract (biceps relaxed)

Levers  The diagram shows the human arm in two positions (straight arm and arm lifted)  The human arm works as a system of levers: –  Long levers are helpful  A lever moves at a pivot  The effort is supplied when a muscle contracts Straight arm Arm lifted

Body Levers  In the arm, where is the pivot?  In the straightening of the arm, which muscle is contracted and in the lifting of the arm, which muscles in contracted?  The biceps and triceps are antagonistic muscles, as they work against each other – what does this mean? Straight arm Arm lifted

Body Levers  The pivot is at the middle, where the arm bends  The triceps contract when straightening the arm and the biceps contract when lifting the arm  The biceps pulls up the arm, but then is stuck… until the contracting triceps pull it back – antagonistic pair Straight arm Arm lifted

Moments  Muscles moving bones act as simple levers – forces can make objects turn if there is a pivot (this turning effect is known as a moment)  To work out moments we need to know the force (weight) applied and the distance from the pivot where the force is applied Pivot Moment (Nm) = Force (N) x Distance (m)

Moments  To work out moments we need to know: -  The force (weight) applied  The distance from the pivot where the force is applied Force (F) Moment (M) Distance (D) Force = Moment  DistanceDistance = Moment  ForceMoment = Force x Distance