Biomechanics - forces Flashcards
What is a force?
the pushing or pulling action that one object exerts on another
What is an internal force?
the actions of your muscles
What is an external force?
another force acting on you E.G gravity
What are the 3 laws of motion?
1) the law of inertia
2) the law of acceleration
3) the law of reaction
What does a force platform measure?
ground reaction forces (GRF)
List the pros of embedded force platforms
- accurate and reliable 3D force measurements
- high sampling frequency and resolution
List the cons of embedded force platforms
- often restricted to indoor use and single step
- possibly unnatural gait (force plate targeting)
- expensive
Which type of force platforms are typically used in labs?
embedded force platforms
What does portable force platforms measure?
vertical force
What is the equation for force?
force = mass x acceleration
What is a triaxial accelerometer?
- measures instantaneous acceleration
- at rest will measure 1 g (1 gravity) due to gravity
- orientation is important
What are triaxial accelerometers often used to measure?
- physical activity
- quantity/intensity
- ‘load’ monitoring
List the pros of accelerometers
- cheaper than lab equipment
- easy to use
- often embedded within other devices
- can monitor closer to the site of interest
List the cons of accelerometers
- valid for intended purpose
- affect the movement being monitored
- battery life
- comfort
What is the equation for weight?
weight = mass x acceleration due to gravity
What is the equation for impulse (Ns)?
impulse = force (N) x time (s)
On a graph what is impulse equal to?
the area
Since impulse = Ft, what does that also mean impulse is equal to?
change in momentum
What is the equation for rate of force development?
rate of force development = change in force/ time taken
What is vertical average loading rate (VALR)?
average gradient between 20-80% of impact peak
What is the vertical instantaneous loading rate (VILR)?
maximum gradient before impact peak
What is the equation for moment?
moment (or torque) = force x perpendicular distance
What is moment?
rotational equivalent of force
What is friction?
a force that acts in the opposition to the movement of one surface over another
What is the equation for friction?
friction = coefficient of friction x normal force
What is normal force?
perpendicular to the surfaces in contact
List the 3 types of friction
- static
- sliding
- rolling
What is fluid friction?
objects moving through a fluid
What are the 2 types of fluid friction?
- aerodynamics (air)
- hydrodynamics (water)
What are the 4 things needed for drag force that affect air/water resistance?
p = density of the fluid
v = relative velocity
A = surface area
CD = drag coefficient
How would you work out the velocities when they are going in opposite directions?
the sum of them both
How would you work out the velocities when they are going in the same directions?
the difference of them
What are the 2 types of flow?
- laminar
- turbulent
List the features of laminar flow
- fluid slides smoothly over
- layers flow in parallel lines
- little disruption to fluid
List the features of turbulent flow
- less orderly (less predictable)
- greater impact on object, slows object
- boundary layer composed of vortices that increase surface friction, more disruption
- common at rear of non-streamlined objects
What are the difference between laminar and turbulent flow?
- turbulent causes more friction
- laminar causes less resistance to movement
What does it mean if there is a greater relative velocity?
- more disturbance of fluid around object
- have to work harder to overcome fluid forces
How can we reduce drag?
- smaller surface area
- slower relative velocity
- more streamlined shape
