Biomechanics Flashcards
FORCE-MOTION
The principle of force motion refers to the application of force to create motion.
This utilises all of Newton’s 3 laws
FORCE
Force is the product of mass times acceleration, represented mathematically as; F= MA
The concept of force is common to all Newton’s Laws.
FRICTIONAL FORCE
Friction is a force that arises when one object or body moves across another – friction always opposes motion. Frictional forces play a large part in changing the state of motion of an object or body.
Four types of friction
- Static friction
Friction between two objects that are not moving - Sliding friction
This occurs when two objects slide
over each other eg sandboarding - Rolling Friction
When one object rolls across another object eg lawn bowls. - Fluid Friction
Friction caused by water / air
NEWTON’S 1ST LAW OF MOTION
A body continues in its state of rest or state of motion unless acted upon by a force”. This law is also referred to as the Law of Inertia.
INERTIA
Is the term used to describe the amount of resistance to a change in an object’s state of motion.
The greater an object’s inertia, the greater the force required to initiate its movement or change its state of motion.
Is directly proportional to an object’s mass
NEWTON’S 2ND LAW OF MOTION
“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”. This law is also referred to as The Law Of Acceleration
The greater the force applied to an object, the faster the acceleration will be.
If the same force is applied to object’s of differing mass, the object with less mass will accelerate faster
Force = mass x acceleration
MOMENTUM
Momentum is a measure of the amount of motion possessed by a moving body and can be expressed mathematically as p=mv
An object can only have momentum if it is moving.
The greater its momentum, the more force that needs to be applied to either stop or slow the object down.
As a result, when two bodies collide, the one with the most momentum will be least affected
CONSERVATION OF LINEAR MOMENTUM
Principle states the total momentum of two objects before and after impact are equal
This occurs in situations where a perfectly elastic collision takes place i.e. one where no energy is lost to sound and heat
cricket example of conservation of linear momentum
When two moving objects collide (cricket bat and ball) the linear momentum is conserved.
By using a relatively slow delivery, when compared with a fast bowler, the momentum of the ball before impact is reduced. Therefore, the bat must be swung with greater velocity if the batsman is to generate the same momentum after impact.
IMPULSE – FORCE-TIME
Impulse is the application of force over a period of time to change the momentum of an object.
The concept of impulse and the impulse–momentum relationship is best described by the following formula:
Impulse = force × time
where force equals the object’s mass multiplied by its acceleration, and time equals the length of time for which the force is applied to the object.
Standing shot putt throw compared with glide and rotation methods– which method would generate the greatest impulse and why?
The longer a force can be applied, and the greater the force that is applied, the greater the object’s impulse or change of momentum.
impulse and tennis racquets
Tennis racquets have different tension strings depending on the user’s individual requirements;
Looser strings – ball on racquet for longer
– more power, less control
Tighter strings – ball on racquet less time
– more control, less po
Cheerleaders often throw an athlete into the air and catch her on the way down.
What two applications of “impulse” can be applied to the image above?
Impulse to increase momentum on the throw;
Maintain contact with the athlete for as long as possible
Apply maximum size force
Impulse to decrease momentum on the catch;
Look to decrease her momentum over the longest time possible
“Give” with the catch by bending at the knees to increase the time over which momentum is taken back to zero
NEWTON’S 3RD LAW OF MOTION
For every action, there is an equal and opposite reaction.
When two objects exert a force upon each other, the forces are opposite in direction and equal in magnitude.
COEFFICIENT OF RESTITUTION (COR)
COR measures the elasticity of the collision between an object and a given surface. It measures how much energy remains in the object after a collision takes place.
An objects COR is measured on a scale of 0→1
A COR of 1 represents a perfectly elastic collision (i.e. When a ball is dropped from a given height the ball will rebound to that same height after colliding with the ground)
A COR of 0 represents a perfectly inelastic collision, effectively stopping at the surface with which it collides (i.e. When the ball is dropped, it doesn’t bounce at all)
COR equation
COR = Height bounced / Height dropped
FACTORS AFFECTING THE COEFFICIENT OF RESTITUTION
Equipment and materials
The temperature of the balls
Velocity of the collission
CONCENTRIC FORCE
ECCENTRIC FORCE
force applied to produce linear motion.
Eg. Hitting a float serve in volleyball.
the off centre force applied to produce angular motion. Eg. Hitting a top spin serve in volleyball.
FORCES THAT CREATE ANGULAR MOTION
torque
Application of an eccentric force
Angular rotation is caused by the application of an eccentric (off-centre) force
When only 1 eccentric force is applied to the object, both linear and angular motion occur (Volleyball top spin serve)
FORCE COUPLES
When two equal, but oppositely directed forces act on opposite sides of an axis of rotation.
TORQUE
Torque is the turning effect created as a result of an eccentric force being applied around a pivot or axis
Torque = Force x Distance or T = F x D
F is the amount of force applied, D = distance between distance where force is applied and the axis of rotation
The longer the moment arm, the greater the rotational force produced for the same amount of force exerted
Torque can be increased and decreased by;
Torque can be increased by;
Applying a greater force
Increasing the length of the moment arm.
Torque can be decreased by;
Applying less force
Decreasing the length of the moment arm
Factors influencing amount of torque placed on the ball?
Amount of force applied (product of muscular contraction)
Length of lever or moment arm – longer moment arm produces increase torque
ANGULAR MOMENTUM
The quantity of angular motion possessed by a rotating body and is expressed mathematically as;
Angular momentum = angular velocity * moment of inertia
MOMENT OF INERTIA
Moment of inertia refers to the resistance of a rotating object to change it’s state of motion
LEVERS
Function - To increase or magnify the force applied
1st class levers
in 1st class levers, the axis/fulcrum is located in the middle with the force and resistance either side. An example of a 1st class lever is a see saw
The further one applies force from the fulcrum, the easier it is to move objects.This allows for individuals to move heavy objects as is seen when using a crow bar
The closer the applied force is to the fulcrum, the greater the effort is needed to move the object.
long force arm= strengths
long resistance arm= speed
2nd class levers
In 2nd class levers the axis/fulcrum is located at the end with the resistance in the middle and force applied at the opposite end An example of a 2nd class lever is a wheelbarrow
THIRD CLASS LEVER
In 3rd class levers, the axis/fulcrum is located at one end with application of the force in the middle and resistance applied at the opposite end.
When looking at the human body, the muscle attachment represents the application of force, the joint usually represents the axis/fulcrum and the weight/load represents the resistance
Maximising lever length at the point of impact ensures maximum speed at the impact or release point
Surface drag and factors affecting
Is the friction produced between fluid and surface of a moving body
Velocity, roughness, viscosity, surface area
form drag and factors affecting
Resistance created by pressure differential between the front and back when moving through a fluid
CSA, velocity, roughness, shape
Wave drag and factors affecting
Resistance formed by creation of waves at the point where and water interact
Velocity, open and closed, technique
