Forces Flashcards
What is biomechanics
The study of the effects of internal and external forces on the human body in movement and rest
How is a forced simply defined
a push or a pull
Forces cause a change in…
The state of motion of an object (start, stop, speed up, slow down, or change direction
Force can either ____ or ____ an object
Accelerate or decelerate
Forces come in ____
pairs: action and reaction
What is magnitude
length of the arrow
What is direction
Relative to an axis
What is line of action
the shaft of the arrow
What is point of application
Where it acts on an object
What is the most familiar unit of measurement for force
Pound or kilopound
What is the SI unit of measurement for force
Newton
What is one N defined as
the force required to accelerate a 1kg mass at 1m/s^2
1N = _____
(1.0kg)(1.0m/s^2)
What is the equation for force
f=ma
What are internal forces
forces acting within the object or system that is being studied
Internal forces can be ____ or _____
compressive (pushing) or tensile (pulling)
What are the internal forces when you land from a jump
A force from your lower leg on your upper leg through your knee and an equal and opposite force from your upper leg to your lower leg through your knee
How do you measure internal forces in biomechanics
strain gauges into cadaver limbs to conduct testing of injury occurrence and prevention
What does a strain gauge or optical fiber on human or animal tendon tell you
The force acting across a tendon and the anthropoemetric location of the muscle
What are external forces
Forces that act on an object as a result of the surrounding
What are two types of external forces
Contact and non-contact
What are 3 non-contract forces
Gravity
magnetic
Electrical
What type of force are air and water resistance
fluid contact forces
Contact forces occur in ____
pairs
We experience gravity as ____
weight
Describe gravity
All objects with mass have an attraction to other objects with mass
What does the magnitude of attraction between items depend on
The amount of mass each object has and the distance between the two objects
The earth attracts someone and the person attracts the earth with ______
equal and opposite force
Gravity acts through our
centre of mass
What is your weight equal to
Your body mass in kilograms muultiplied by the acceleration due to gravity
What is normal force
The component of the force of the ground acting on us perpendicular to the contact surface
What is the normal force when we are on a surface parallel to the horizontal
equal in magnitude to the force of gravity and opposite in direction
What occurs to gravity and normal force when we are on a slanted surface
The force of gravity vector still points directly towards the centre of the earth but the normal force stays perpendicular to the contact surface and is no longer equal and opposite to the magnitude and direction of the force of gravity
The parallel force is also called the
shear force
How does the parallel/shear force aact
down the slope
What happens to the force component on a slope
Increase in slope = increase in the magnitude of parallel force, decrease in the magnitude of perpendicular force
What do we need to know if order to resolve for the components of force on a slant surface
Angle of the slant
mass of the object
What are the steps to resolving for the components of force on a slant surface
- Draw the diagram with the axis system and all known forces
- Solve for the magnitude of gravity (W=mg)
- Solve for the direction of the force of gravity relative to the axis system
- Solve for the parallel and perpendicular components of force
what axis is top to down
z
what axis in back to front
x
what axis is side to side
y
What axis are forces acting in when walking
z and x and y
What is used to measure external force in biomechanics
strain gauges Force transducers (force plate and instrumented treadmill, pressure mats)
What are 4 types of strain gauges
- Force transducers (force plates, load cells)
- Springs
- Piezoelectric crystals
- Dynamometer
How do strain gauges work
An applied force will cause an object to deform and this deformation is measured and amplified by the electronics
What is a down size of strain gauges
expensive
What is used in clinical settings to measure external force
force transducers
What is a held dynamometer determine
- Muscle strength
- Weaknesses
What is the gold standard measurement of force in biomechanics
forceplate and instrumented treadmill
What are the mechanics of forceplates and instrumented treadmill
Have strain gauges or force plates measuring components attached to a device to measure forces in multiple dimensions when looking at different tasks
What are the pros to force plates and instrumented treadmills
- accurate measure of ground reaction force
- Reliable
- Multidimensional
What are the cons of force plates and instrumented treadmills
- Difficult to use in the field
- Cannot measure foot pressure distribution
- Very expensive
What is an inexpensive alternative to measuring force
Pressure
What is the equation for pressure
P = F/A
What is pressure
The force per unit area directed perpendicular to an object surface
how do pressure sensors work
Most common pressure sensors measure pressure using the piezoresistive effectn
What is the piezoresistive effect
It is a change in the elctrical resistivity of a semiconductor or metal when mechanical strain is applied
What does piezo mean
to squeeze or press
what are the pros to pressure sensing technology?
- portable
- thin
- flexible
- lightweight
- approximation of force
- accurate for timing of foot loading
- can measure foot pressure distribution while force plates cannot
What are the cons to pressure sensing technology
- Unidimensional (vertical loading)
- Degree of precision, accuracy and reliability requires testing
what does the unidimensionalism of pressure sensing technology mean
you can only measure in the direction that the sensor is orientated. will not measure all the component of the force
What is the F-Scan foot pressure mapping system? What does it do
Portable In-shoe pressure sensor. Quantifies force, contact pressure distribution, and timing. Extremely thin and high resolution
The foot is the …
end point effector with the ground
Foot….. provides valuable insight on a variety of biomechanical variables
foot pressure distribution and timing information
Changes in foot landing and pressure distribution is related to…
changes in knee/hip and ankle joint angle during contact in running
What are changes in the joints during forefoot running
The knee is more extended, the ankle more plantarflexed and the hip in greater extension than in heel strike running at impact
What occurs when training in minimalist shoes
Plantar pressure starts higher in all areas and then changes to have more forefoot pressure and less heel pressure
How do pressure sensors compare to the gold standard in magnitude and kinematics
Well!! both have M-profile
What is centre of pressure
the instantaneous point of application of the ground reaction force
What can measuring foot centre of pressure movement during walking tell us
about the point of application of the GRP vector and how we use our feet while walking
how do we use our feet when walking
Work in s shape from heel to big toe
How do instrumented insoles and force plate compare when measuring centre pressure
match well until reaching the toe where they divert because of less sensors surrounding toe
How were pressure sensors used in track sports and what was found
to monitor the timing and movement of the legs or the athlete. Concluded that the timing of the steps support and release phase has a great importance in performance and the pace of steps should increase towards the end of the throw event
how were pressure sensors used in snowboarding
to improve their skill by analyzing the dynamics of the weight distribution inside their boots. essential for identifying the weight shifting techniques
How do you make instrumented devices
adding force and pressure sensors to mobility devices to measure the forces that individuals produce during activity
In foot strike patterns what are the stages called
force development, Impact transient, peak
What is force developement
the slope
What is impact transient
the first mini peak
when comparing shoes on and shoes off what was found
no shoes had greater force development and had more intense impact transient
How does hindfoot running compare to forefoot running
forefoot running has no impact transient and decreased force development and slight increase in force development
does forefoot running with or without shoes have greater impact transient
without shoes
What are two methods to approximate internal forces
- Inverse dynamics
- electromyography
