Biomechanics Flashcards
Define Positive Work
Object displacement is in the same direction as the force applied.
Define Mechanical Work
Work is equal to:
The amount of force applied to an object and the distance moved by the object.
What is the Formula for calculating Work?
Work = Force x Distance (F.s) (joules/Nm)
How do you calculate work if it is applied at an angle?
Work = Force x Cos {0} x distance (s)
{0} = the angle between the force vector and the line of displacement
Define Negative Work
Object displacement is in the opposite direction to which the force is applied.
Define Net Work
Sum of positive and negative work
Can be 0
What is an example of 0 work in the body?
Isometric muscle contractions
e.g. muscle length remains unchanged like when you hold a weight with your arms outstretched
Define Power
The rate of doing work
The amount of mechanical work done in a given time.
What is the equation for Power?
Work/ change in time
Or
Force x distance / Time
What is Power measured in?
Watts or Joules/Seconds
How can you use velocity with respect to Power and Force
Power = Force x Velocity
Define Inertia
Inertia is an objects resistance to change in its state of motion.
Proportional to the body’s mass
Scalar quantity
Symbol – m, units – kg
Define Momentum
Momentum is the quantity of motion possessed by an object
Remember velocity has a time component - so how fast something is going.
Describe the relationship between velocity and displacement in terms of graphical representation.
Velocity is directly proportional to the gradient of a displacement time graph. Therefore negative displacement = negative velocity.
When resolving forces what is the golden rule?
resolve forces only when they are perpendicular to the lever.
What does a clockwise force produce
Negative moment
Define Force (inc units)
Force is the interaction between two or more objects.
Measured in Newtons (N)
What is Newtons 1st Law of Motion
Law of inertia:
An object will remain at rest o continue to move with constant momentum in a straight line, unless it is acted upon by a net external force.
Inertia is a force - True or False
False - It is not a force
How do you calculate Angular Momentum?
Inertia (m) x Angular Velocity
What is inertia proportional to?
A Body’s mass
Define Newton’s Second Law of Motion
Law of Acceleration
The rate of change of momentum is proportional to the force causing the change and takes place in the direction of the applied bet force.
Force = Mass x acceleration
Define Pressure
Pressure is the measure of the distribution of force over the surface area of contact
P = Force / Area
Describe the 3 different types of loading
Tensile (force < —— > )
Compressive - pushing in from both sides >——<
Sheer loading
Define Stress
A normalised measure of load
How would you calculate compressive or tensile stress
s = F/c.s.a s = sigma F = compressive or tensile load c.s.a = cross sectional area
How would you calaculate Sheer Stress?
Shear Stress t = F/c.s.a
where F= shear load and c.s.a = cross sectional area parallel to load
Define Strain
A normalised measure of deformation
How would you calculate Compressive or Tensile Strain?
Compressive or Tensile Strain e = dl/L
where L= original length and dl = change in length
How would you calculate Sheer Strain?
Shear strain = dq/q
where q= original angle and dq= change in angle
What does Young’s Modulus E = s/e describe?
Elasticity of a given material.
What Momentum does a static object have?
None
How can you change the momentum of an object?
In order to change the momentum of an object and hence velocity of an object we can either change the magnitude of the force or the time over which it acts.
REMEMBER the impulse momentum relationship
Ft = m2v2- m1v1
Describe the relationship between velocity, displacement and time
Velocity = change in displacement / change in time
How would you calculate Net force (ie during a standing vertical jump)
Ground reaction force - Body weight = Net force
If to objects collide what will happen to their impulse?
Momentum is always conserved (it cannot be lost)
So will stay the same.
Define Energy
The Capacity to do work
Measured in Joules
What are the 2 main types of energy studied in this module?
Potential energy and Kinetic energy
Define Kinetic energy
Ability of a moving object to do work due to its motion
How do we calculate Kinetic energy?
KE = 0.5mv^2
remember you can rearrange this equation to get velocity
Define non eccentric force v eccentric force
NE = Transnational force E = rotational force - is a force that acts off centre
Define Moment of Force
Moment of Force: The torque caused by an eccentric force
How do you calculate torque ?
Force x Length
How do you calculate torque if the force is being applied at an angle?
T= FxLsin{0}
What 3 things can manipulate torque?
Change the magnitude of Force applied
Change the angle of which the Force is Applied
Change the moment arm length
Is clockwise rotation positive or negative?
Clockwise = negative
anti clockwise - positive
Define Lever
A rigid bar that rotates about an axis/ fulcrum
Define First Class Lever
The applied force and resistive force are on opposite sides to the fulcrum
note they do not need to be equidistant from the fulcrum.
Define Second Class Lever
The applied and resistive forces are on the same side of the fulcrum axis
The resitive forces are closer to the fulcrum axis
Third Class Levers
The applied and resistive force are on the same side of the axis
The applied effort force is closer to the fulcrum axis
Which type of lever are most muscle bone lever systems for concentric contractions?
Third Class Levers
What is leverage?
The mechanical advantage gained by a lever.
What is Mechanical advantage?
Moment arm force / moment arm resistance
note remember this is a ratio of the forces so you do not need to work out moments - distance have no effect
What is a force couple?
Force couple: A pair of equal parallel forces acting on opposite sides of an axis of rotation (rotation without translation)
Define Angular Inertia.
An Objects resistance to starting to rotate or changing rate of rotation.
What is angular inertia a function of?
Body Mass
The distribution of the mass relative to the axis of rotation.
Moment of Inertia Formula =
State Units
I = mr^2 (Kg.m2)
m = mass of particle r = radius of rotation
- Define the function of a lever with the following mechanical advantage
MA = 1
then lever alters direction of motion
Define the function of a lever with the following mechanical advantage
MA < 1
MA < 1 then velocity of movement is greater as effort force acts over smaller distance so resistance force therefore moved over greater distance in same time
Define the function of a lever with the following mechanical advantage
MA < 1
MA < 1, and the effort arm is less than the resistance arm. In this case, a much greater effort force is required to overcome the resistance force.
The effort force acts over a small distance, however, with the result that the resistance force is moved over a much greater distance in the same amount of time
When MA < 1, therefore, velocity or speed of movement
is said to be magnified.
Define the function of a lever with the following mechanical advantage
MA > 1
MA > 1 then lever magnifies effort force as greater torque generated by greater effort arm
Describe the Impulse Momentum Relationship
The concept that it takes an impulse (force multiplied by time) to change the momentum (mass multiplied by velocity) of an object
Define impulse
Force multiplied by time or the area under a
force by time curve.
