Biomechanics Flashcards
Define Force and how its measured?
- An influence that may cause a body to alter its state of motion.
- Measured in newtons
Define concentric force
-Force applied to produce linear motion
Define eccentric force
- Force applied to produce angular motion
- rotational force
- occurs when force is applied away from the COG of an object.
- results in angular velocity
What is the conservation of momentum principle?
-The conservation of momentum principle states that when an object is moving it has momentum and as long as no force is applied to speed the object up or slow it down its momentum is said to be conserved.
So in basic terms when a collision occurs the total momentum before the collision should be equal to the momentum after the collision.
What is newtons first law?
- An object at rest will remain at rest and a moving object will continue moving unless acted upon by an unbalanced (external)force.
- Known as inertia
- Greater mass = greater inertia
What is newtons second law?
- The rate of change of acceleration to a body is proportional to the force applied to it and inversely proportional to the mass of the object.
- Represented by F=ma
What is newtons third law?
- For every action there is an equal and opposite reaction.
- Forces work in pairs opposing one another.
What is momentum?
- The momentum of an object is equal to its mass multiplied by its velocity.
- P= m x V
- P=momentum
Define impulse
- Impulse is the change in momentum.
Impulse = Force x time
- Area under line in graph is the impulse
State the relationship of impulse and creating force and in turn velocity.
- The greater the impulse the greater the greater the change in momentum and therefore the greater the force produced and therefore the greater the velocity of the object.
State the relationship of impulse when absorbing force.
- The greater the impulse the greater the change in momentum and therefore the lower the peak force of the object.
- Lower peak force = less risk of injury
Why in sports do people use a ‘follow through’?
- This is because using a follow through will increase the time of contact with the ball increasing the change in momentum (impulse) and thus increasing the velocity of the object allowing it to travel a further distance.
- More momentum = more velocity
- Also prevents object from deaccelerating before release
Define co-efficient of restitution.
- A value representing the ratio of velocity after an impact compared with the velocity before the impact.
COR = 1 = collides elastically (linear momentum fully conserved ) perfect
COR= 1< - imperfect elastic Collison (normal)
COR= 0 - Object does not bounce at all (linear momentum not conserved at all)
What are the 3 main factors that effect COR?
- The materials of the intersecting bodies, e.g. new tennis ball have higher COR then old and different surfaces clay vs grass
- The velocity of the Collison - Higher velocities reduce COR because greater compression of ball thus greater difference between the velocity before and after
- The temperature of the materials involved - Higher temperature = Higher COR
What are the three main parts of a lever?
- force/effort
- fulcrum/pivot
- resistance/ load
What is the resistance arm of a lever?
- The distance between the resistance and the fulcrum
What is the force arm of a lever?
- The distance between the force and the fulcrum.
What is a first class lever?
- A lever which has the fulcrum between the force and the resistance
- when fulcrum is in middle balanced movements are made, when fulcrum is closer to force speed and range of motion is optimal, when fulcrum is close to resistance optimal force is produced
What is a second class lever?
- when the load is between the fulcrum and the force.
- Produce forceful movements since large resistance can be moved by relatively small force. e.g. wheel barrow
What is a third class lever?
- A lever which has the force located between the fulcrum and the load.
- effective at producing speed due to their large range of motion
- Large amount of force required to move small resistance
- Most common type of lever in the body, e.g. Bicep
What does mechanical advantage mean?
- If the force provided is multiplied by the lever system to produce a greater output.
- Levers with a larger force arm than resistance arm will offer a mechanical advantage
- Second class levers always offer mechanical advantage.
Speed (levers)
- Third class levers are optimal for fast actions as they have relatively larger resistance arm than force arm.
- Force arm move over small distance = move resistance arm larger distance
What are the factors effecting lever use?
- Length of lever = greater velocity and momentum but less accuracy (e.g. golf)
- Inertia of lever - Heavier the lever the harder it is to rotate
- Amount of force -The amount of force an athlete is able to generate via their muscles determines the length of the lever the athlete should use.
What is a rotational force?
- A rotational force is called a eccentric force and occurs when force is applied away from the COG of an object
- eccentric force develops angular velocity
What is angular momentum?
- Quantity of motion an object possess when rotating about an axis.
- angular momentum = angular velocity x moment of inertia
Define moment of inertia
- The distribution of the objects mass about the point that is used to rotate the object.
- It is the resistance to rotational motion.
e.g. diver in tuck position has a low moment of inertia as during tuck position more mass is located closer to axis of rotation thus allowing faster spins.
What are the 2 factors that effect fluid resistance?
- Density - the more dense the fluid the more disturbed the fluid becomes thus the greater the resistance, e.g. humid
- Viscosity - The more viscous the fluid the more disturbed the fluid becomes hence the greater the resistance. e.g. honey
Define boundary layer
- When a fluid moves past a solid surface a thin layer develops adjacent to the surface where frictional forces hinder the motion of the fluid.
Define Turbulent flow
- when fluid particles from adjacent layer become mixed.
- tends to stick to object thus creating smaller pocket of low pressure reducing drag.
- dimples in golf ball cause turbulent flow causing it to travel further as less drag
Define laminar flow
- When fluid particles travel along smooth well ordered non - intersecting paths, or layers.
- Tends to break away from surface creating lager pocket of low pressure behind object increasing drag
Explain Boundary layer separation
- where the boundary layer breaks away from an object.
- earlier break off = greater area of air flow behind increasing drag
- later break off = smaller area of air flow and thus less drag
Define drag
- Drag is the fluid force that opposes the forward motion of the body and reduces the body’s velocity.
What is surface drag ( frictional drag), what factors affect it and how is it reduced?
- drag which is derived from friction between the surface of a body and the fluid which it is moving through.
- factors effecting surface drag - fluid temp, viscosity, bodies SA, velocity of object
- To reduce surface drag
reduce relative roughness of surface ( wear tight swimsuit)
and reduce SA in contact with fluid.
What is Form drag? Factors that affect it? And how is it reduced?
- Drag created by the pressure difference between the front and rear of an object.
- Factors which effect form drag velocity of the body and size of its SA
- Reducing form drag:
streamlined shape, smoothness, aerodynamic position.
What is Wave drag? and how is it reduced?
- Resistance made by the generation of waves where two different fluids such as air and water meet.
- factors effecting wave drag, greater up and down motion and increased speed
- reducing wave drag limit up and down movements, create more aerodynamic shape at front of object.
What is Bernoulli’s principle?
- The principle which states that there is an inverse relationship between the velocity of a fluid is flowing and pressure.
- States that in areas of high velocity of fluid movement, pressure will be low and in areas in low velocity, pressure will be high.
-An object will move from areas of high pressure to low pressure.
What is the angle of attack?
- The angle at which an object is released.
- A symmetrical object released without any angle will not experience lift.
- There is an optimal angle to increase lift.
What is the magnus effect?
- The term used to describe the effect of rotation on objects path as it moves through a fluid.
What is the effect of top spin on a ball?
- The effect of top spin on a ball causes a downwards magnus force causing the ball to drop suddenly.
- This is as due to the top spin of the ball the particles at the top of the ball collide with the air particles causing their to be a low velocity area on top of the ball and a high pressure area on top of the ball.
- and on the bottom of the ball there is a high velocity of air traveling resulting there to be a low pressure area.
- Therefore the ball dips as it moves from high to low pressure
How does backspin effect a ball?
- The effect of backspin causes a upwards magnus force in the ball causing it to stay in the air for longer.
- This is as the backspin causes the layer of particles on top of the ball to increase in velocity creating a low pressure area.
- And the backspin of the ball causes the particles underneath to have a lower velocity as they collide with the relative airflow. Thus as there is a lower velocity there is a higher pressure area.
-Therefore the ball has a upwards magnus effect as the ball moves from high to low pressure, thus causing the ball to stay in the air for longer.
What are the effects of back spin, top spin and no spin on rebound height?
- Top spin shot bounces low and fast
- Backspin shot will bounce slow and high
Define summation of force
- The way that body segments interact to produce force.
How is power optimised in summation of forces context?
- The stronger and larger muscles of the thighs and trunk are moved first followed by the smaller and faster muscles.
- Sequentially accelerate each body part with correct timing so that optimum momentum passes from one body part to the next.
- Use as many body parts/segments as possible, so force can be applied over the maximum possible time.
- Follow through is important to prevent deceleration of last segment and safe dissipation of force.
- Ensure all forces are directed towards the target.
How is accuracy optimised in the context of summation of forces?
- Less segments needed and force is summated simultaneously.
Define Balance
- The ability to neutralise forces which disturb equilibrium
Define base of support
- The area around the outside of the body that is in contact with the ground.
Define Centre of Gravity
- The imaginary point where mass is equally distributed in every direction
