Linear/Angular Kinetics Flashcards
What is a force?
Push or pull acting on the body
*vector
A vector has?
Magnitude
Direction
Point of application
How is a force represented?
Graphically by line of action/resultant
Forces are measured in
Newtons
… Newton is the force required to give a mass of …. Kg and acceleration of … m.s*2
1
1
1
Explain Newtons 1st law
THE LAW OF INERTIA: the state of a body will remain unchanged unless an external force is applied to it.
- if a body possess mass then it also has intertia
- so if a body is at rest it wants to stay that way
What is intertia?
The reluctance of a body to change its state
What is important to remember about inertia?
The force required to overcome intertia is proportional to the mass
What external forces are acting in the keg toss?
Air resistance
Gravity
Explain newtons 2nd law
THE LAW OF ACCELERATION: net force is equal to mass times acceleration
F = m X a
What happens if intertia is overcome?
The state of motion will change and we will have an acceleration - increasing or decreasing speed
SI unit of mass
Kilogram
SI unit of weight
Newton
Acceleration due to gravity
g= 9.81 m/s2
Explain newtons 3rd law
For every action there’s an equal and opposite reaction
What do we need to exert a force?
Friction
How do friction and newtons 3rd law relate?
When we apply a force to the ground:
The ground applies a force back on us
Add 2nd law and your body accelerates
3 external forces acting on the body
Friction
Impact
Gravitational
What are friction forces?
Oppose the relative motion or tendency of such motion of two surfaces in contact
What are impact forces?
Occur when two or more bodies collide
What are gravitational forces?
The force of attraction between masses
3 examples of forces acting inside the body
Contact
Friction
Muscle
What are contact forces?
Occur when 2 or more bodies are in contact
What are muscle forces?
Forces caused by the contraction of muscles
What are free body diagrams?
Include ALL of the external forces acting on a body
* if airborne and aerodynamic forces are neglected, this involves just the weight of the body
Pressure equation
Area
4 factors affecting GRF
Body mass
Speed
Type of foot strike/ gait surface
Footwear - reduced loading rates, cushioning
What is a ground reaction force?
A force applied to the ground/floor is equally matched by the reaction force of the floor/ground.
- all surfaces produce a reaction force
- if you push against the ground, the ground pushes back with a force equal in magnitude but opposite in direction.
How is GRF commonly measured?
Force platform
How do you measure forces?
KISTLER
Mass 42kg
Accuracy 2% within 10-10,000N
3 components of GRF
Fx
Fy
Fz
How do you calculate magnitude?
Resultant force (Fr) = ¥ ( Fy2 + Fz2 )
How do you calculate direction?
Angle to horizontal (@)
tan@ = opposite/ adjacent
tan@ = Fz/Fy = …….
@ = tan-1
What is the moment of a force?
Defined by a force acting at a distance about an axis of rotation
Moment of a force equation
Moment = force x distance M = F x D (N.m) = (N) x (m)
What is a moment arm?
Exists between the joint axis (fulcrum) and muscle force (effort)
- when a muscle contracts its pulls on its point of attachment along a line of action
What is the moment of intertia?
Refers to the resistance of a body to change its state of angular motion
* intertia depends on objects mass
Moment of intertia equation/unit
I = m. r2
(m= mass of segment/body, r= distance from axis of rotation)
kg.m2
Explain forces at an instance in time
EF = m.a
If acceleration is zero= static analysis
If acceleration is non-zero = dynamic analysis
*when a body is completely MOTIONLESS, it is considered to be in a STATIC EQUILIBRIUM
Dynamic analysis equations
E f Horizontal = m.a Horizontal
E f Vertical = m.a Vertical
E m 2 = 1 g A
What are the 2 conditions for motion?
- The resultant force (Fr) is related to the acceleration of the object
- The resultant moment (Mr) is related to the angular acceleration of the object
7 biomechanical principles that apply in the vertical jump
Acceleration Velocity Displacement Time Newtons 2nd law Vertical force Newtons 3rd law
Impulse equation
Force x time
Define impulse
Determines the effect of a force applied to a body over a period of time
*the product of force and time and thus is represented by the area under the force-time curve
What is graphical integration?
The process by which the area under the curve is found
Method and implication of graphical integration
Counting squares
- time consuming/ prone to error
What is the trapezium rule?
Assumes that over small time gaps, the area under the force-time curve approximates a trapezium
Trapezium rule equation
1/2 x (f1 + f2) x T
* total area under curve = sum of each individual trapezium
What is linear momentum?
A measure of the quantity of motion, taking into account both the mass of the body and its linear velocity
- faster a body of a given mass moves - greater momentum
- greater a body’s mass - larger momentum at given velocity
Linear momentum equation/unit
M = m X v
- kg. m.s-1
What is the impulse-momentum relationship?
The impulse of a force is equal to the time rate of change in momentum
Impulse-momentum equation
F*t = mv - mu F*t = m (v)
