Studied by 5 people
LINEAR KINETICS
Newton’s 1st Law?
Law of inertia
A body remains at its current state of motion (constant velocity) unless acted upon by an external force
What is inertia? Relationship between inertia and mass?
Tendency of an object to keep the current state of motion
Difficulty in changing the state of motion
Inertia is proportional to mass of an object
Mass=measure of inertia in linear motion
Newton’s 2nd Law?
Law of Acceleration
An external force applied to a body causes acceleration
F=ma? If F=0, what happens?
Force= Mass/ Acceleration
Acceleration= Force/Mass
If force is equal to zero, then acceleration is zero because they are proportional to one another
Meaning of Net Force
Sum of all the forces acting
Resistance vs. Propulsion
Minimize friction as resistance
Lubrication-synovial fluid (m=0.01)
Skating - gliding
Tire inflation & paving
Maximize friction as source propulsion
Source of horizontal GRF
Cleats: prevent slipping
Skating - push off
Newton’s 3rd Law?
Law of Reaction
For every force (action), there is an equal and opposite reaction.
What is reaction?
Same magnitude
Opposite direction
EX:
Bullet vs. Gun
Fist Fighting
Propulsion in swimming (pushing water behind you)
Hockey players
Ground Reaction Force (GRF)?
Reaction supplied by the ground
Passive force
Importance of the GRF?
Important for human motion
Major external force that accelerates the body
Speeds up
Slows down
The only external force one can voluntarily control
Weight is always constant & downward
How Does a high jumper utilize the GRF during takeoff?
Slow-down of rightward (+) velocity
Slow-down of downward (-) velocity
Speed-up of upward (+) velocity
Law of Gravitation?
All bodies are attracted to one another due to their masses
Properties of gravitation
Proportional to masses
Inversely proportional to (separation distance)^2
Weight? Relationship between weight and mass?
Gravity exerted to a body by the earth
Weight= (mass)(gravitational acceleration)=mg
Direction: downward
Passes through the COM of the body
Gravitational acceleration?
9.81 m/s^2 in downward direction towards the earth
Friction?
Force acting at the are of contact between two surfaces
Source of horizontal GRF
Magnitude
Proportional to
Normal reaction force (N)
Friction coefficient (WEIRD U)
Cannot exceed your force
Direction
Opposite that of motion or motion tendency
Friction Proporties
Friction coefficient
Force
Sliding friction vs. Rolling friciton
Sliding friction
Friction due to relative motion of the surfaces
Rolling friction
Friction due to temporary deformations of the surfaces
Sliding vs Rolling
Sliding friction >> rolling friciton
Beneficial to convert sliding to rolling for smaller friction
Static friction vs Kinetic friction?
Static friction
Ff experienced with no motion (F=Ff)
Max. static friction = force required to initiate motion
Kinetic (dynamic) friction
Ff experienced during motion (F>Ff)
Force required to maintain motion once initiated
Max static friction
Max. static friction = force required to initiate motion
Force required to initiate motion and force required to maintain the motion?
Max. Static Friction: force required to initiate motion
Kinetic (dynamic) Friction: Force required to maintain once initiated
Your Force vs. Friction? Net Force?
Force is a push or pulls acting on a body that causes a motion
Net force is the sum of all the forces acting
Friction is the force acting at the area of contact between 2 surfaces
Lubrication vs. Friction? Role of synovial fluid in a synovial joint?
Lubrication decreases friction. Synovial fluid reduces friction in the joints which in turn reduces injury between bones.
Resistance vs. Source of propulsion
Minimize friction as resistance
Lubrication- synovial fluid (m = 0.01)
Skating - gliding
Tire inflation & paving
Maximize friction as source of propulsion
Source of horizontal GRF
Cleats: prevent slipping
Skating- push off
Friction vs. Horizontal GRF
Friction
Force acting at the area of contact between 2 surfaces
Source of horizontal GRF
Used as a source of propulsion to MAXIMIZE friction
Ex. Soccer Cleats, Ice skates
Momentum? Its Importance?
Amount of motion
M=mv
Vector
Direction=direction of velocity
Important in giving & receiving impact, collision etc.
Unit: kg*m/s
Important in giving & receiving impact, collision, etc
Principle of momentum conservation?
If no external force, total momentum remains constant
Impulse?
The accumulated effect of force exertion over a period of time
Vector quantity: direction= direction of force
Unit: Ns
Causes change in momentum
Strategies in giving/ receiving impulse?
Giving impulse (batting, throwing, etc)
Maximize impulse by maximizing the momentum of the apparatus (batting)
Elongating elapsed time
Receiving impulse (landing, catching, etc)
Reduce impulse, if possible
Reduced impulse force/ pressure by increasing time/area
Mechanical Work?
Force applied against a resistance
Accumulated effect of force exertion over a displacement
Work = (force)(displacement)
Scalar
Unit: J (Joule) =Nm
Positive work vs. Negative work
Contribution vs taking away
Determined by the angle between f &d
If THETA > Pi/2 rad (opposite), negative work
Muscle Contraction types vs Work?
Concentric contraction: positive work
Eccentric contraction: negative work
Isometric contraction: no mechanical work
Work while overcoming the gravity (weight): mountain or stair climbing?
Mountain
Stair Climbing
Mechanical Power?
Rate of work
Intensity of work
Rate of energy generation/consumption
Power= (work)/(elapsed time)
Power= (force)(velocity)
Unit: W (Watt)= J/s
Scalar
Mechanical Energy? Potential vs Kinetic?
Capacity to do mechanical work
Mechanical energy (ME) = Potential E + Kinetic E
Potential (PE): energy due to vertical (height)
Kinetic (KE): energy due to motion (velocity)
Scalar
Unit: J
Mechanical energy conservation? Diving ex?
If gravity is the only external force acting on a system, ME remains constant
EX: Diving (work causes a change in mechanical energy of the system
Positive work: Increases energy of the system
Negative work: Decrease energy of the system
Note
Flashcard