biomedhanics so far

how does height of COM affect stability?

Lower centre of mass, greater stability

how does base of support affect stability?

the wider the base, the greater the stability

what is the line of gravity and how does it effect stability?

• an imaginary line which extends down from the centre of mass to the floor

• keeping line of gravity within the base of support helps maintain stability

what is stability able to withstand?

external forces

what are 4 factors that affect stability?

• mass of the body

• height of centre of mass

• base of support

• line of gravity

how does mass affect stability?

the greater the mass, the greater the inertia, so the more stable it is

explain how high jumpers use COM and stability to their advantage?

• Curved run-up creates angular momentum for rotation.

• At take-off, arms drive upwards to raise the centre of mass (CoM) and increase vertical lift.

• The athlete rotates so their back faces the bar and arches into the Fosbury flop shape.

• This curved body position moves the CoM to below the body, so the CoM can pass at or below the bar while the body clears it.

• This makes the jump more efficient and increases the chance of clearing a greater height.

what is stability?

the ability of a body to resist motion and remain at rest

what is the centre of mass?

the point at which a body is balanced in all directions

what does centre of mass rely on?

• the distribution of the body mass

• can be manipulated to improve performance

what is a sporting example of a footballer using COM for performance?

• footballer will raise hands above head when jumping for header to raise COM to enable them to jump higher and remain in air for longer

example of how starting on blocks to running race using COM and stability to advantage

Crouch position (“on your marks”)

• Large base of support

• Low COM

• Line of gravity within base of support

• Stable position → helps balance/control

Set position

• Hips raised → COM higher

• Base of support effectively smaller

• Line of gravity near/outside front of base

• Unstable position → allows quick acceleration

Drive/run phase

• Line of gravity outside base of support

• COM pushed forwards

• Very unstable → maximises forward acceleration out of blocks

what are the 3 most common ways of analysing performance?

• limb kinematics

• force plates

• wind tunnels

what is limb kinematics?

• Method of analysing movement of body segments when performing a task

• Usually takes place in lab

• High speed cameras and computer software capture the movement of an athlete who is wearing motion capture material

what are force plates?

• Work by measuring the amount of force that is applied to the ground when an action is performed on them

• Can be used to study: balance, walking gait, jumping, movement etc.

• Different types of force plates (in floor, on bar etc.)

what are wind tunnels?

• Sports that are effected by wind tunnels are affected by air resistance so can use wind tunnels to try minimise impact by studying how air moves over object

• Uses sensors and airflow vision (e.g. smoke or lasers) to analyse aerodynamic efficacy

what are some pros of using limb kinematics to analyse performance?

• Improves performance analysis

• Good for technique analysis

• Non-invasive and safe 

• Good for injury prevention (can identify dangerous technique etc)

what are some cons of using limb kinematics to analyse performance?

• Has to be done in a lab

• Specialist equipment required

• Doesn’t show forces

what are some pros of using force plates to analyse performance?

• Accurate measure of force

• Good for assessing power

• Helps identify injury risk

• Good at assessing force imbalances

• Can asses best techniques to produce most force

what are some cons of using force plates to analyse performance?

• Very expensive

• Requires technical expertise

• Limited to specific movements (e.g. jumps and landings not sprinting, changing direction etc.)

•  lab style

what are some pros of using wind tunnels to analyse performance?

• Good for analysing aerodynamics

• Can improve technique to improve aerodynamic and so enhance performance

• Allows for equipment to be tested so the best can be used (e.g. helmets, bike frames etc.)

what are some cons of using wind tunnels to analyse performance?

• Very expensive

• Requires specialist staff

• Time consuming set up

• Unrealistic - not on a track etc.

what are some sports that may use limb kinematics to analyse performance?

• Running

• Gymnastics

• Football

• 100m sprinter might use limb kinematics to check their "knee lift" height. If the data shows their knee isn't reaching the optimal angle, they can adjust their technique to gain more power in each stride

what are some sports that may use force plates to analyse performance?

• Basketball

• A netball player can use a force plate to see if they are pushing off equally with both legs during a jump. If the data shows the left leg is weaker, the coach can create a specific gym program to balance them out.

what are some sports that may use wind tunnels to analyse performance?

• Cycling - A cyclist might test different "tuck" positions to see which one creates the least resistance.

• Luge

• Engineers use tunnels to design "slippery" helmets, skin-tight suits, and bike frames that slice through the air more easily.

what does force create?

motion

what are the 5 effects of force?

1. Create motion

2. Accelerate a body

3. Decelerate a body

4. Change direction of a body

5. Change shape of a body

what are some sporting examples to show a force that can:

1. decclerate an object

2. create motion

3. change the shape of a body

4. change the direction of a body

5. accelerate a body

A sprinter slowing down after crossing the finish line

A footballer kicking a stationary ball

A gymnast compressing a springboard before take off

A tennis player hitting a ball back

A swimmer pushing off the wall to increase speed

what is a net force?

the sum of all forces acting on the body

what are the 2 types of forces?

• internal

• external

what are internal forces?

• Produced by things inside of you

• Produced by muscular contractions acting on the skeleton

• e.g. rectus femoris to extend the knee in the 100m sprint

what are external forces?

• Produced by things outside the body

• e.g. weight, reaction, friction, air resistance

what is friction?

the force that opposes the motion of two surfaces in contact

what is friction measured in?

Newtons

what are some factors that affect friction?

• Roughness of the surfaces in contact

• Temperature if the surfaces in contact

• Size of normal reaction

what type of force is air resistance?

a horizontal force

what is air resistance?

the force that opposes the motion of a body travelling through the air

what is air resistance measured in?

Newtons

what factors is air resistance effected by? (4)

1. the velocity of the body

2. shape of the body

3. frontal cross-sectional area

4. smoothness of the surface

what is an example of how sports performers adapt themselves and their equipment to reduce air resistance?

• the luge performer lies as flat as possible to reduces frontal cross section and wears smooth clothing to reduce air resistance

• In sports like sailing or paragliding the larger the cross-sectional area the better

what is a free body diagram?

A free body diagram is a simple drawing used in biomechanics to show:

• An object or body

• All the forces acting on it

• The direction and sometimes the size of those forces

They help analyse movement in sport

which way does friction go normally when you are running or walking?

forwards

what is the force that pushes you off the floor and up?

reaction

what is the centre of mass?

the point at which a body is balanced in all directions

what does centre of mass rely on?

the distribution of the body mass and can be manipulated to improve performance

what is an example of how a performer may manipulate their centre of mass to enhance performance?

a footballer will raise their hands above their head when jumping for a header to raise the centre of mass to enable them to jump higher and remain in the air for longer

what is stability?

• the ability of a body to resist motion and remain at rest

• ability to withstand forces

what are some factors that effect stability? (4)

• Mass of the body - the greater the mass of the inertia

• Height of the centre of mass - the lower the centre of mass the greater the stability

• Base of support - the wider the base of support the greater the stability

• Line of gravity -  is an imaginary line which extends down from the centre of mass to the floor, keeping the line of the gravity within the base of support to maintain stability

why does the mass of the body affect stability?

the greater the mass, the greater the inertia

why does the height of the centre of mass affect stability?

• the lower the centre of mass the greater the stability

why does the base support affect stability?

• the wider the base of support the greater the stability

why does the line of gravity affect stability?

• Line of gravity is an imaginary line which extends down from the centre of mass to the floor, keeping the line of the gravity within the base of support to maintain stability

what is the general name of Newtons first law?

Law of inertia

what is the general name of Newtons second law?

Law of acceleration

what is the general name for Newtons third law?

Law of reaction

what is Newtons first law?

A body continues in a state of rest or uniform velocity unless acted upon by an external or unbalanced force

what is inertia?

• the resistance an object has to change its state of motion.

• The larger the object the greater the mass if the object the greater the inertia

what are some sporting examples where Newtons first law applies?

• A golf ball will remain stationary on a tee with gravity acting upon it, until the golf applies an external force to it

• A tennis ball will remain stationary in your hand unless someone throws it up applying an external force

• A penalty in football where the ball will remain stationary unless someone applies an external force (e.g. kicking it)

what is Newtons second law?

A body's rate of change of momentum is proportional to the size of force applied and acts in the same direction as that force

how can Newtons second law be explained?

• The quantity of motion is known as momentum and is related to acceleration.

• This means that the acceleration is proportional to the size of force applied

what are some sporting examples where Newtons second law applies?

• The harder to golfer hits the ball and the larger the mass of the club, the further the ball will travel

• The harder the footballer strikes and the larger the mass of the player, the further the ball will travel

what is Newtons 3rd law?

• For every action force applied to an object, there is an equal and opposite reactions

• The action force is applied as the muscles cause the skeletal system to apply force to the ground or surface involved, the surface will then apply the same force back onto the skeleton to create movement in the opposite direction

what are some sporting examples where Newtons 3rd law applies?

• The swimmer pushes against the wall in a tumble-turn and the wall applies the force back to the swimmer who moves in the opposite of the action force

• When a tennis player hits a ball back the ball hits the racket and moves the ball in the opposite direction

within Newtons laws there are 4 key concepts which can be calculated to get the quantities of force and movement achieved. what are these 4 things?

1. Velocity

2. Momentum

3. Acceleration

4. Force 

what is velocity?

the rate of change of displacement

what is momentum?

the quantity of motion possessed by a moving body

what is momentum measured in?

Kilograms metres per second (kgm/s)

what is the equation for momentum?

momentum = mass x velocity

what is acceleration?

the rate of change in velocity

what is the equation for acceleration?

Acceleration = (final velocity - initial velocity) / time taken

what is acceleration measured in?

Measured in metres per second per second (metres per second squared) (m/s/s)(m/s^2)

what is velocity measured in?

metres per second

what is force?

a push or pull that alters the state of motion of an object

what is the equation for force?

force = mass x acceleration

what is force measured in?

Newtons