Noadswood Science, 2012

The Arm & Moments

To know the structure of the arm and to be able to work out moments

Wednesday, April 19, 2023

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 upBiceps 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 Distance Distance = Moment Force Moment = Force x Distance