Week 1 Flashcards
Newton's Laws, Force Systems, Levers
- Law of Inertia
Body remains at rest or in a state of uniform motion in a straight line unless acted on by an unbalanced force
- Inertia is a property of an object that makes the object resist both the initiation of motion and change of motion (acceleration)
Static equilibrium (law of inertia)
Dynamic equilibrium (law of inertia)
moving at consistent speed
o Linear dynamic equilibrium
o Angular dynamic equilibrium
- Law of Acceleration
acceleration of an object is proportional to the unbalanced forces acting on it and inversely proportional to the mass of the object
A = force / mass
F = mass x acceleration (acceleration from no movement to any movement is proportional to force and direction that caused it)
Force acceleration (LOA)
- Force Acceleration, Linear - More force is needed to accelerate heavier car to same speed
- Force Acceleration, Rotation – Torque, the ability of the force to cause rotation of the lever, force perpendicular to lever arm
Moment Arm
shortest distance between the action line and the joint axis (perpendicular distance from the axis to the force vector)
T = F x perpendicular distance to axis, or moment arm
Angular Motion
Angle of Application – angle between the application of force and fulcrum
* Optimal angle of pull to generate most torque (rotary force) is 90 degrees
*Any angle not 90 means not all of the force is rotational
* Longer segment makes it harder to move
tuck = fast, layout = slow
Momentum (LOA)
- The time over which a force is applied
- Slow app of force – low momentum
- Quick app of force – high momentum
F = mass x acceleration
F = mass x (Velocity/Time)
F x Time = Mass x Velocity
F x Time = Momentum - Large force and Long time means high momentum
Impulse (LOA)
Moment of impact
Work and Energy (LOA)
- Work is force applied over a distance
- Does not take time into consideration
- Process of transferring energy
- Potential energy – stored energy
- Kinetic energy – action taking place
Power (LOA)
- Doing work with a specific time frame
- Squat and jump have the same work, bc a jump takes less time is has more power
- Inverse relationship to time
- Less time for movement – more power
- Law of Reaction
for every action there is an equal and opposite reaction
* Force always comes in pairs, equal in magnitude and opposite in direction
Force Systems
- Linear
- Concurrent
- Parallel
Shear Forces
moves or attempts to move an object. Parallel to contacting surfaces and in the direction of the attempted movement
Friction
this force potentially exists whenever two objects contact
- Will have magnitudes whenever the 2 objects try to slide on each other
- Comes in pairs, equal and opposite, applied to each contacting surface
- Direction of force of friction is always opposite the direction of movement
Static vs Kinetic Friction
Static - maximal potential force (Frs) is the product of a constant value and the magnitude of the contact force
Kinetic Friction – once an object is in motion, friction is a constant value (Frk)
- Always smaller than the value for static friction
Lever Components
- Lever – rigid bar revolving around a fixed point
- Fulcrum – axis, point of rotation
- Effort arm (Ea) – distance from the application of effort force to axis
- Resistance Arm (RA)- distance form application of resistance force to axis
First Class Lever
axis in the middle (teeter totter, triceps at olecranon process)
Second Class Lever
resistance in the middle (wheelbarrow, going up on toes)
- Efforts arm is always longer than resistance arm- advantageous for the effort force
Third Class Lever
effort force is in the middle
- RA is always longer than the effort arm, favors ROM
- Most muscle systems in body
Mechanical Advantage
Measure of the mechanical efficiency of a lever system
- Relative effectiveness or ease of the effort force to overcome the resistance
Mechanical Advantage = Effort Arm/Resistance Arm
- Mechanical advantage is >1 – easier to do
- Mechanical advantage is <1 – harder to do
Parallel Force Systems
Two or more parallel force systems act on the same object but at some distance from each other
Action lines do not intersect
- Need to understand the principle of levers and torque
