biomechanics Flashcards
linear motion
• the movement of a body in a straight line, all parts move the same distance, direction and time.
• It is created by a direct force that passes through the centre of mass.
distance
•The length of a path taken by a body moving from one position to another
• measured in metres
displacement
•The shortest straight line route between two positions (as the crow flies).
•measured in metres
speed
• The movement of a body per unit of time (without reference to direction)
• measured in metres per seconds
speed equation
distance/time
velocity
• The rate of change of displacement/speed in a given direction
• measured in metres per second
acceleration/ deceleration
•The rate of change of velocity
• measures in metre per second per second
acceleration/ deceleration definition
Change in velocity (final – initial) /Time
angular motion
• when a body (or part of a body) moves in a circle or part of a circle about an axis of rotation.
• is created or initiated by an eccentric force which passes outside the centre of mass or axis.
longitudinal axis
from the head to the foot of the body. Rotation around it causes the twisting action in diving, gymnastics or figure skating. (Body works in transverse plane)
frontal axis
from the front to the back of the body. Rotation around it causes “cartwheel” action. (Body works in frontal plane)
transverse axis
from the left to right side of the body. Rotation around it causes “somersault” action. (Body works in sagittal plane)
moment of inertia
• Reluctance of a body to change its state of angular motion or rotation
• measured in kgm^2
moment of inertia calculation
Sum of the mass multiplied by the distance of the mass from the axis of rotation squared
I=Σmr^2
angular velocity
• The rate of spin in a particular direction or angular displacement per unit of time
• measured in Radians per second (rad/s)
angular velocity calculation
Angular velocity (ω) = angular displacement ÷ time
ω = d/t
angular momentum
• The amount of angular motion of a rotating body
• measure in Kilogram metres squared per second: kgm2/s
angular momentum calculation
Angular momentum (L) = moment of inertia (I) x angular velocity (ω)
L = Iω
factors effecting the moment of inertia
• mass
• The distribution of the mass about the axis of rotation
mass effecting moment of inertia
• The larger the mass of the body (or body part) the larger the moment of inertia
For example, it takes less torque (turning force) to initiate spin on a 1kg discus than on a 2kg discus
The distribution of the mass about the axis of rotation effecting moment of inertia
• The closer the mass of the body (or body part) is to the axis of rotation, the smaller the moment of inertia
For example, in a tuck somersault the body mass is closer to the transverse axis than in a pike somersault. Moment of inertia is smaller and so angular motion can be changed more easily.
fluid mechanics
Fluid mechanics is the study of the factors that impact the magnitude of air resistance and drag. Air resistance and drag are both types of fluid friction and have a huge impact on the performance of all sports
air resistance
the force acting to oppose the motion of a body through the air
drag
the force acting to oppose the motion of a body through a fluid
effects of air resistance and drag
• An athlete wants to put all of their energy into maximising performance and not waste it overcoming forces that hold them back
• Air resistance and drag act against the motion of a body and place and increased physiological demand, leading to early fatigue and poor performance.
• By altering body position, equipment design and clothing an athlete can minimise air resistance and drag and gain a significant advantage.
Factors which affect the magnitude of air resistance and drag
• Velocity
• Mass
• Front cross-sectional area
• Streamlining and shape
• Surface characteristics
velocity and drag
The greater the velocity, the greater the air resistance or drag.
In sport, high velocity is usually beneficial to performance. Therefore we don’t want to reduce it meaning that we have to find alternative ways to reduce air resistance or drag.
mass and drag
The mass of a body affects what happens to its motion as a result of air resistance and drag. The greater the mass, the less its motion is changed by these forces.
Bodies with small mass slow down quickly due to fluid friction.
front cross-sectional area and drag
This is the area of the part of the body that presents first to the fluid it is moving through. The smaller this are is, the less fluid friction acts
streamlining/shape and drag
Fluid friction is minimised by using the optimal shape or position; this reduces turbulence and smooths the air or water flow around a body
surface characteristics and drag
This is the smoothness of the surface of a body. Smooth surfaces create less air resistance or drag than rough surfaces.
air resistance with temp and altitude
• Difference in air temperature and altitude also affect air resistance, which is of great importance in sports such as football and golf as the distance of travel and spin on the ball will be affected.
- As air temp increase, density decreases which reduces air resistance
- As altitude increase, density decrease which reduces air resistance
air resistance with temp and altitude
Difference in air temperature and altitude also affect air resistance, which is of great importance in sports such as football and golf as the distance of travel and spin on the ball will be affected.
- As air temp increase, density decreases which reduces air resistance
- As altitude increase, density decrease which reduces air resistance
projectile motion
A projectile is a body that is moving within a fluid, not in contact with the ground. Fluids include air and water.
factors affecting horizontal distance travelled
• Height of release - The level from which a projectile is released compared to the level of the landing surface.
• Speed of release- How fast a body is travelling at the moment it becomes a projectile.
• Angle of release - The projection angle of the object, measured between the horizontal and the direction of the projectile at release.
height of release
The higher the release height from the landing height, the further the horizontal distance travelled.
Eg. A raised tee in golf leads to the ball travelling further before landing
speed of release
The greater the speed of release, the further the horizontal distance travelled.
Eg. A fast arm in javelin throwing leads to greater distance
angle of release
The optimal angle of release is 45* if the height of release is the same as the landing (long jumper) but lower is landing height is lower than release (shot put)
projectile motion and resultant force
Once a body is in flight, there are two external forces acting upon it (weight and air resistance) . These can be drawn on as a free body diagram and the resultant lines can be used to calculate the ‘resultant force’.
projectile motion and resultant force
Once a body is in flight, there are two external forces acting upon it (weight and air resistance) . These can be drawn on as a free body diagram and the resultant lines can be used to calculate the ‘resultant force’.
weight - free body diagram
• Acts vertically downwards from the centre of mass
• Size of W arrow depends on the mass
air resistance- free body diagram
• Acts in the opposite direction to the direction of motion, drawn from the centre of mass.
• Size of the AR arrow depends on the factors previously discussed.
parallelogram of forces
• This method uses a parallelogram (a four sided shape where opposite sides are parallel to each other) to show the size and direction of the resultant force acting on a body.
• Start with two force arrows with a common origin.
• A parallelogram is drawn where opposite sides of the shape are parallel to the force arrows, and drawn with a dotted line. The resultant force arrow is drawn diagonally across the parallelogram from the origin of the two forces.
what are the patterns of flight
• parabolic
• non-parabolic
parabolic
A uniform curve that is symmetrical around its highest point
non-parabolic
A curve that is not symmetrical about is highest point
parabolic flight
• If weight is the only force acting on a body, then its flight path is parabolic.
• So if weight is the dominant force acting on a body (because the body has a large mass) and it has very little air resistance, then the flight path shape is very close to being parabolic or symmetrical. Eg: Shot put
non-parabolic flight
• If weight is small, and air resistance is large then the flight path shape is non-parabolic or asymmetric. Eg: Badminton shuttle
• This is because the force of air resistance is able to overcome the inertia (small mass) of the body, and decrease its velocity.
• Decreasing velocity causes decreasing air resistance.
• As the flight continues the body becomes increasingly under the influence of its weight, rather than air resistance.
• The parallelogram of forces shows that the size of the resultant force decreases, and the direction it acts in becomes further from the direction of AR. (Increasing angle between AR and R)
This gives a non- parabolic flight shape.
principles of flight
• The faster fluids flow, the less pressure they exert. The slow fluids flow, the more pressure they exert. This can create a lift force on a projectile.
• Within sports, projectiles can be shaped with a curved side to change the speed of air flow and take advantage of this lift force. This force can be upwards or downwards.
Bernoulli’s Principle and Performance
Upwards lift force:
• The upwards lift force reduces the impact of weight.
• The resultant force has a smaller downwards component.
• Flight time is extended and therefore the horizontal distance travelled increases.
• The flight path is made non-parabolic.
reverse aerofoil
• Reverse aerofoil: An aerofoil positioned with its curved surface facing downwards and its flatter surface facing upwards, causes downforce.
• Downforce: A force pushing downward on a body eg: on an F1 racing car.
• A reverse aerofoil also causes a difference in the air flow above and below it: the Bernoulli principle is the same, but the high and low pressures are on opposite sides of the aerofoil compared to the previous example of the ski jumper
magnus force
Top spin:
At the top of the ball, the airflow is in the opposite direction to the spin of the top surface of the ball.
This slows the air and causes high pressure.
Top spin:
At the under side of the ball, the airflow is in the same direction as the spin of the bottom surface of the ball.
This speeds up the air and causes low pressure.
Top spin:
A pressure differential is formed.
There is higher pressure above the ball than below it. This causes a downwards force called the Magnus force.
The effect is to make the ball dip in flight
