Biomechanics Flashcards
what is newtons 1st law
Law of intertia
“ a body continues in a state of rest or motion in a straight line, unless compelled to change that state by an external force “
what is newtons 2cnd law
law of acceleration
“ the rate of momentum of a body is proportional to the force causing it and the change that takes place in the direction in which the force acts “
what is newtons 3rd law
law of reaction
“ to every action force, there is an equal and opposite reaction force “
what is the definition of inertia
resistance of a body ( object ) to change its state of motion e.g. having to apply more force to a weighted ball
application of newtons 1st law
when kicking a rugby ball of a tee, the rugby ball will remain at rest on the tee until an external force is applied by the rugby players foot to the ball
application of newtons 2cnd law
when kicking a rugby ball of a tee, the greater the size of the force applied by the player to the ball, the greater the rate of change momentum and acceleration towards the post. The ball will accelerate in the same direction as the force applied towards the post.
application of newtons 3rd law
when kicking a rugby ball of a tee, a forward and upward “action force “ is applied to the ball from the players foot. The ball will apply an equal and opposite force to the players foot.
what is a scalar quantity
a scalar quantity is when measurements are described in terms of just their size or magnitude
what are examples of scalar quantities
- speed
- distance
define speed
the rate of change of position and can be calculated by distance divided by time
speed is in metres per second
define distance
the length of the path of a body follows when moving from one position to another
what is the centre of mass ( coM )
the point of balance in the body
usually between the hip region ( naval )
males coM is usually higher than females
what are the four factors affecting stability
1) the height of coM - lowering coM will increase stability
2) position of line of gravity - should be central over the base of support becomes, and the stability increases
3) area of the support base - more contact points, the larger base of support becomes , stability increases
4) mass of performer - greater mass , more stability because of increased inertia
what is the lines of gravity
the lines that extends vertically downwards from coM and determines if the body is stable or not
how can you maximise stability
- crouched position - low coM
- large base support
- line of gravity falls within base of support
- weight- high mass
how can you minimise stability
- raise coM
- lower base of support
- weight
what are the two main functions of levers
- to generate muscular effort to overcome a given load
- to increase the speed of a given movement
what are the 3 main components of a lever
- fulcrum ( pivot )
- resistance ( load to be moved )
- effort ( source of energy )
define the fulcrum
part of the lever system
point about which the lever rotates
define what resistance is
in the lever system
the weight to be moved by the lever system
define what effort is
part of the lever system
the force applied by the use of the lever system
what is a lever
bones
- rigid structures which roate around a fixed point
- known as the fulcrum
what is the fulcrum
in the human body the fulcrum is the joint
what is the effort
the muscles that surround the joint create internal forces that move the bones they are attachted to
when a muscle contracts an effort is created
what is the load
in the lever system
weight or resistance
if the effort is large enough to overcome the effort it wil pull on the lever to create movement
what is a first class lever
fulcrum lies between the effort and resistance
e.g. extension of the elbow, holding a javelin
what is a second class lever
resistance is between fulcrum and effort
e.g. ball of foot during plantar flexion is used during take off phase of high jump
what is a third class lever
effort is between the fulcrum and the resistance
e.g. lifting a weight
what is the effort arm
the distance between the fulcrum and the effort
what is the load arm
the distance between the load and the fulcrum
why do longer levers generate greater forces
because the load arm becomes longer and therefore can give greater acceleration to projectiles on release
what are the mechanical advantages/ disadvantages of a second class lever
- mechanical adavantage to move large load with small effort
- operates at the ball of the foot vertically accelerate an athletes whole weight easily
- but efficiency is over a small ROM and is at expense of velocity
what are the mechanical advantages/ disadvantages of a third class lever
- mechanical disadvantage as it requires a large effort to move a relatively small load
- operates at the knee joint during extension to kick a football
- but it can move the load at high velocity over a large ROM
define the force arm
lever sytsem
length of line between where the fulcrum and resistance are labelled
define the resistance arm
length of line between where the fulcrum and resistance are labelled
what is mechanical advantage
when the force arm is longer than the resistance arm. This means that the lever system can move a large load over a short distance and requires little force.
However, it has a small range of movement and is difficult to generate speed and distance.
what is mechanical disadvantage
when the resistance arm is greater than the force arm. This means that the lever system cannot move as heavy a load but can do it faster. It also has a large range of movement.
what is impulse
the time it takes a force to be applied to an object or body and can be calculated as force X time
what is the result of an increase in impulse
results in an increase in the rate of change of momentum, which causes a large change in velocity
what is impulse equivalent to
a change in the momentum of a body as a result of a force acting upon it
momentum ( kgms ) = mass X velocity
what can impulse be used for in a sporting environment
to add speed to a body or object or slow down on impact. This can be achieved through increasing the amount of muscular force that is applied.
what is net impulse
a combination of positive and negative impulse
on a force - time graph, where should the positive and negative impulse be
- positive = above the line
- negative = below the line
what are the two types of forces
- internal = generated by skeletal muscles
- external = comes from outside of the body
why do both internal and external forces act on a performer during linear motion
internal muscular forces allow a runner to contract their skeletal muscles to generate force required to produce movement at the same time external forces will also act on a runner
what are the five effects caused when force creates motion
1) force can create motion
2) force can accelerate a body
3) force can decelerate a body
4) force can change direction of a body
5) force can change the shape of a body
in what two ways do external forces act upon the body
1) vertically - moves a body up and down
2) horizontal - moves a body forwards and backwards
what happens when a net force is 0
there will be no change in motion as the forces are balanced. The body will remain at rest or will continue to travel with constant velocity.
what are the two vertical forces
1) weight = the gravitational force exerted on an object
2) reaction force = occurs when two bodies are in contact with one another
what is the equation for weight
weight ( N ) = mass X acceleration due to gravity
what are the two horizontal forces
1) friction = occurs when two or more bodies are in contact with another
2) air resistance = a force that acts on the opposite direction to the motion of the body travelling through the air
what are the two types of frictional forces
1) static = the force exerted when there is no motion between two surfaces
2) sliding = the force exerted when motion is occurring
what is friction affected by
- roughness of the ground surface
- roughness of the contact surface
- temperature
- size of normal reaction
what is air resistance affected by
- velocity
- shape
- frontal cross sectional area
- smoothness of the surface
what is a free body diagram
a clearly labelled sketch showing all of the forces acting on a body at a particular instance in time
where are vertical forces drawn on a free body diagram
weight - always drawn downwards from the centre of mass
reaction - starts where two bodies are in contact and drawn upwards
how are horizontal forces drawn on a free body diagram
friction - starts from where two bodies are in contact and in the same direction as motion
air resistance - drawn from the coM opposing the direction of motion
what is net force
the resultant force acting on a body when all other forces have been considered. Discussed in terms of balanced vs unbalanced forces.
what is a balanced force
when there are two or more forces that are equal in size but opposite in direction
what is an unbalanced force
when a force acting in one direction is larger than a force acting in the opposite direction
what happens when the friction force is equal in length to the air resistance
the net result is zero
what is linear motion
the movement of a body in a straight line or curved line, where all parts of the body move the same distance, in the same direction over the same time.
what is a direct force
a force applied through the centre of mass resulting in linear motion
what is centre of mass
the point at which a body is balanced in all directions.
The point from which weight appears at
what are the measurememts used in linear motion
- mass
- weight
- distance
- speed
- acceleration
- displacement
- velocity
- momentum
what is the definition of scalar
when measurements are only described in terms of size and magnitude
what is the definition of vector
when measurements are described in terms of their size, magnitude or direction
what is the definition of mass
the quantity of matter the body possesses
what is the definition of distance
the path a body takes as it moves from starting position to a finishing position
what is the definition of displacement
the shortest route in a straight line between the start and finish
what is the definition of speed
the bodies movement per unit of time with no reference to direction
what is the definition of velocity
rate of change of displacement
how fast a body travels in a certain direction and is the rate of change in displacement
moment of inertia : mass
- the greater the mass the greater the moment of inertia
- sports with a high degree of rotation are often performed by athletes with a low mass
- the low mass decreases moment of inertia and the resistance to change state of rotation, so the athletes can start rotation, change the rate of rotation and stop rotation with relative ease
moment of inertia : distribution of mass from axis of rotation
- the further the mass moves from the axis of rotation, the greater the moment of inertia
- movements where the mass is tucked around the axis of rotation gives a lower moment of inertia
what happens with the recovery leg in running with regards to moment of inertia
mass is distributed close to the axis of rotation at the hip, therefore moment of inertia is low - the resistance to rotation is low and the leg moves back to the ground quickly
what happens with the drive leg in running in regards to the moment of inertia
mass is distributed far away from the axis of rotation at the hip therefore moment of inertia is high - the resistance to rotation is high and the leg moves slowly
how does moment of inertia effect angular velocity
if MI is high, resistance to rotation is high, therefore angular velocity is low - the rate of spin is slow
vice versa
what is the definition of angular momentum
the quantity of rotation a body posseses
( to spin )
involves an object or body in motion around an axis
it depends upon the moment of inertia and angular velocity
what is equation for angulat momentum
angular momentum= moment of inertia X angular velocity
these two are inversely proportional
what must happen before angular momentum is generated
in the prepartion of a take off phase of a rotational movement pattern, an eccentric force or torque must be applied
what is conservation of angular motion
once AM has been generated it is a product of moment of inertia and angular velocity. As MI increases, AV decreases. This means that once angular has been generated, it remains constant and does not change throughout the movement
What is the conservation of angular momentum
Once AM has been generated it is a product of moment of inertia and angular velocity decreases and vice versa. This means that once AM has been generated, it remains constant and does not change throughout the movement. A performer can keep rotation going for a long time.
What is the definition of angular motion
Movement around a fixed point
Occurs when a force is applied outside of the centre of mass ( eccentric force )
What is a torque
The rotational consequence of a force
What is the equation for the moment of force ( torque )
Moment of force = force X perpendicular distance from the fulcrum
What is the angular analogue for newtons 1st law
A rotating body will continue to turn about its axis of rotation with constant angular momentum unless an external rotational force is exerted upon it.
What is the angular analogue for newtons 2nd law
The rate of change of angular momentum of a body is proportional to the force causing it and the change that takes place in the direction which the force acts
What is the angular analogue for newtons 3rd law
When a force is applied by one body to another the second body will exert an equal and opposite force on the other body
What is angular distance
The total angle a body turns through from start to finish position when rotating about an axis
Measured in degree and radians
What is angular displacement
The smallest change in angle between the start and finish position of a body rotating about an axis
Measured in degrees and radians
What is angular displacement
The smallest change in angle between the start and finish point of a rotation
How to convert degrees into radians
1 rad = 57.3 degrees
? Degrees / 57.3
What is angular velocity
The rate of change of angular displacement
What is angular acceleration
The rate of change of angular velocity
How to calculate angular accel
Change in angular velocity in rads per seconds / time taken in seconds
