Transcript Skeleton Investigation

THE ARM & MOMENTS
Noadswood Science, 2012
Friday, July 17, 2015
The Arm & Moments
 To know the structure of the arm and to be able to work out
moments
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
Moment
(M)
Force
(F)
Force = Moment  Distance
Distance
(D)
Distance = Moment  Force
Moment = Force x Distance