L15-17;C12 Flashcards
Explain the following and how they differ:
Kinematics
Kinetics
Kinematics- explains what is occurring to the object (how fast, acceleration, etc)
Kinetics- Explains the ‘why’. Why can object is in motion
An objects natural tendency is to _______ _______
Preserve motion
_____ is a measure of inertia (also resistance to change motion)
_____ is the pull of gravity on a mass
Mass, weight
______ is the change of position over time. This formula is ____ over ____
Velocity,
Delta D over Delta T’
What is considered the “quantity of motion” ?
Momentum
What is the formula for momentum?
M=m x v
What is Newton’s first law with respect to kinetics?
The quantity of motion will stay unchanged unless there is an action
What is the conservation of momentum formula?
(m.v)f=(m.v)i
What will happen to momentum if no force is applied?
It will stay unchained
What is a force?
This is something that changes the momentum of an object.
Since mass is usually constant in kinetic problems, what must happen to velocity?
Velocity must be the factor that changes.
What is Newton’s second law with respect to kinetics?
A force is proportional to change in momentum per unit of time, F=ma
What do we observe when we see an accelerating body? (Force wise)
We view the net forces acting on the object
What is the impulse momentum relationship?
Since force is equal to mass x acceleration, and acceleration equals v/t, impulse is F•∆t=∆M=(m•v)f-(m•v)i
What is Newton’s third law with respect to kinetics?
Every action has an equal or opposite reaction
When standing, GRF _ mg
When leaving the ground and jumping, GRF __ mg
=, >
Explain the application to force plates during jumping:
Stiffer jumping-
Softer lading-
Stiffer jumping- creates more force, in a short period of time
Softer landing- creates less force, but takes more time (more beneficial for athletes and less prone to injuries)
Explain how joint shape influences landing.
Joint shape influences if the landing will absorb or produce more force. If we don’t change joint shape, the time is a lot shorter.
When do frictional forces occur?
Frictional forces only occur when external forces apply.
They also occur whenever two surfaces in constant attempt to move or cross each other
The reaction force only arises due to what other force?
The action force.
Resistance arises in the direction opposite to ______ ______
Impending force
Explain the formula of friction. Also provide it.
The magnitude of the frictional force is the product of the coefficient of friction and normal reaction force
Ff= μ•R [N]
For static objects, friction is ______ or ______ to applied forces
For dynamic objects, friction is ______ and _____ than maximal static friction
Equal, opposite
Constant, less
μs is always ____ than μk
Greater
What is linear momentum defined as?
The quantity of motion
Explain linear momentum’s units, and how it’s calculated.
Linear momentum is a vector and measure by m•v and units are Kg•m/s
Change in momentum is directly related to what law?
Newton’s first law
Explain what elastic and plastic collisions are. What will happen to the energy during collisions?
Elastic= objects collide and bounce off each other retaining shape Plastic= objects collide and stick together
Also all energy put in will be lost in some quantity over time due to deformation and friction.
In these situations, velocity of the system is ________, therefore, relative velocities are the same after and before. What is the formula.
Conserved
(m1v1+m2v2)i= (m1v1+m2v2)f
Explain what happens in plastic collisions
At least one object deform and does not regain original shape. Objects do not separate and velocity is not conserved
During linear momentum, what instants are we mainly measuring?
We are looking at the instant in time where acceleration and mass relate to force
When does impulse (F•∆t=∆M) only apply?
This only applies if a constant force is throughout
What is mechanical energy? Scalar or vector? What’s it measured in?
Energy is the capacity to do work, it is a scalar and measured in Joules. It has two factors, potential and kinetic.
True or false: objects not in motion still have potential to produce energy
True
What is the formula for positional and deformational potential energy?
Positional: Mgh
Deformation: 1/2kx^2 (K is stiffness, x is distance deformed)
What is kinetic energy?
Objects that have the capacity to do work. This is energy in motion.
What is the formula for kinetic energy?
KE: 1/2m•v^2
What is the difference between energy of position and energy of deformation?
Energy of position= gravitational potential energy (PE) of athletes whole body
Energy of deformation= strain energy (SE) in the resistance bands
What is the energy conservation law?
In the absence of externally applied forces other than gravity, the total mechanical energy of a system remains constant.
What is the conservation of energy equation?
PEf+KEf=PEi+KEi
The ____ performed by externally applied forces other than gravity can _______ the energy
work, Change
What is the work energy relationship equation?
W=∆E=∆PE+∆KE+∆TE
What is mechanical work? Explain work of a force. What is the equation?
This is work done by a force or an object. Work of a force when Applied, displaces an object,. If the object is displaced, work is done.
W=F•∆p
True or false: all forces do work. Explain.
False, only where the position of application undergoes displacement.
True or false: work can be positive, negative, and zero.
True.
Is work a scalar or vector?
Scalar
What does positive and negative work mean?
Positive work- means object has gained energy
(Force does positive work when in same direction as displacement)
Negative work- means object has lost energy
(Force does negative work when against the opposite of displacement)
What are the two rules for work?
- Time must elapse for work to be done (displacement must occur)
- Not all forces do work (no displacement in direction of applied force means negative work)
Biomechanical work states that muscles produce two types of work. Explain them and what they’re called.
External work: muscles function together to do work on the environment
Internal work: muscles function together to do work to move our body segments
What is mechanical power is it a scalar or vector? whats it units?What is the equation?
Power refers to the rate at which work is done. The amount of work performed over a given time interval: w/∆t
Work and power are scalar quantities measured in watts
Energy can be _________, if energy of a system has changed the nthat means work has been ______
Transferred, done
_____ is the process that will change the state of energy
______ is the state,
Work
Energy
during running, GRF is _____ times the body weight
2-3x
True or false: all bodies are attracted to one another and have a force proportional of M•a. This is inversely proportional to the square distance between them.
True
What forces usually act on momentum?
Friction and air resistance
Explain the coefficient of restitution. What happens if it’s closer to 1? To 0?
The coefficient of restitution dictates how a collusion will occur. More elastic, closer to 1. More plastic, closer to 0. Increasing impact, velocity, and temperature increases coefficient of restitution.
What are the units for work and power?
Work= joules Power= watts
