Biomechanics Exam 3

Law of inertia

all about the mass

Law of acceleration

the amount of acceleration of a body id proportional to the acting force and inversely proportional to the mass of the body

Newtons first law of motion

an object will not change its motion unless acted on by an unbalanced force

Will objects with a greater mass have more or less interia?

more

The law of action and reaction

for every action there is an equal but opposite reaction

Inertia

property of a physical object by which it continues in its existing state of rest. or uniform motion in a straight line, unless that state is changed by an external force

Linear Inertia

mass (kg)

Linear kinetics deals with

the cause of linear motion (force and mass)

What is force?

something that tends to change the motion, accelerates or deforms an object

Force Unit

pound and newton (N)

Equation for force

F=ma

1N of force is required to accelerate a….

1kg mass 1m/s^2

External Forces

forces that act on an object as a result of its interaction with the environment surrounding it

Internal Forces

forces that act within the object of system

The total force of 68.6N is applied on the weight with a mass of 4 kg. What is the total linear acceleration?

17.15m/s^2

Examples of external forces

air resistance, body weight (apply on the center of gravity), ground reaction force

Center of Mass (COM)

the point where all the mass of a body is concentrated, the point about which a body would balance without a tendency to rotate

Center of Gravity (COG)

the vertical projection of the center of mass to the ground

Center of Pressure (COP)

the point where the resultant of all ground reaction forces act

Examples of interal forces

our muscle forces, and joint forces

Mass

measures the amount of matter in an object

Is mass a scalar or vector quantity?

scalar

Weight

is the force of gravity acting on an object

Is weight a scalar or vector quantity?

vector

What does the force of gravity cause?

the gravitational acceleration or acceleration de to gravity (g)

Equation for weight(w)

mg

Does a medicine ball or a sponge ball have a greater resistance?

medicine ball

Momentum

quantity of motion or mass in motion

Another way to describe momentum

how much mass is in how much motion

Momentum equation

mass*velocity

Is momentum a vector quantity?

yes

Impulse

product of force and the time during which the force acts

Impulse equation

force*time

Is impulse a vector?

yes

Impulse units

N*s

Impulse-momentum equation

Ft=m(vf-vi)=p

Does impulse change momentum?

yes

Force applied for a period of time can either ___ or ____ the velocity of an object

increase or decrease

When impulse and momentum are in the same direction what will happen?

impulse will increase momentum

Example of impulse and momentum moving in the same direction

throwing

When impulse and momentum are in the opposite directions, what will happen?

impulse will reduce momentum

Example of impulse and momentum in opposite directions

tackling

What is the muscle force?

force

What is the velocity of the object of the body?

velocity

If you increase the optimal time that force applies, what will happen to the velocity?

velocity will increase

Isometric contraction

muscle contracts but does not shorten

Concentric contraction

muscle shortens

Eccentric contraction

muscle lengthens

Novice athletes tend to exert force over

shorter periods of time

Skilled athletes exert force

over longer times, they build up more force using more muscle groups

Skilled athletes motion produces

high impulse and more accurate

When impulse and momentum move in opposite directions what kind of muscle action is that?

muscle counteraction is eccentric

During bob and bills fight bob threw a punch that was in contact with bills face around .1s. if bills face with the mass of 5kg was at rest before the punch then reached to the velocity of 25 m/s, what was the total force that bob applied to bills face?

1250 N

The area under the force-time graph is?

impulse

higher area of impulse means

higher change in velocity

lower area of impulse means

lower change in velocity

Is there a higher of lower GRF during running?

higher, less contact time during running

Braking impulses reduces

horizontal velocity (momentum)

Braking impulses means

impulse and momentum are in opposite directions

Propelling impulse increases

horizontal velocity (momentum)

Propelling impulse means

impulse and momentum are in the same direction

What does horizontal impulse tell us?

how we can tell if someone is speeding up or slowing down

Speeding up

braking<propelling

constant velocity

braking=propelling

slowing down

braking>propelling

Muscle force impulse equation

muscle force (eccentric contraction) * time

If muscle force (eccentric contraction) is positive that means that

muscle force impulse is positive

If body velocity is negative (body goes down) that means that

body momentum is negative

more force absorption means

using more eccentric force

When muscle force impulse is slowing down the body velocity that means

more force absorption, higher muscle force impulse, smooth motion, land with lower GRF, and less risk of injury

Higher muscle force impulse (higher force over longer time) means

lower landing velocity and less impact or landing impulse (lower GRF)

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?

using a force platform

vertical GRF is about

140% of body weight

anterior-posterior (AP) GRF is

20% body weight

medio-lateral (ML) GRF

5% body weight

The vGRF in walking is what shaped?

camel

The first peak of vGRF in walking is?

from heel contract to mid stance

The second peak of vGRF in walking is?

during terminal-stance before push off when the force is still pushing the ground back

The vGRF during running shaped

like a bell

in heel strike runners there is a small peak

before the main vGRF peak

the small peak in heel strike runners is called

passive/transition/impact peak

in forefoot runners the shape is perfectly

a bell

the small peak in heel strike runners is related to?

the transition between heel to tow

when is there no impact or passive GRF

during a forefoot running strike

horizontal GRF or AP GRF is the

horizontal component of the total GRF

Horizontal GRF (Rx) is negative from

initial contact to mid-stance (deceleration)

Horizontal GRF (Rx) is positive from

mid-stance to toe off (acceleration)

kinetic energy equation

KE=1/2mv^2

potential energy equation

PE=mgh

Is the vGRF greater during landing or jumping?

landing

during landing what does the body have

gravitational acceleration

The landing velocity will increase by the landing height and

how the muscle can absorb the force (soft vs stiff)

Stiff landing

higher vGRF, shorter contact time

Soft landing

lower vGRF, longer contact time

stiff landing characteristics

exert force over shorter periods of time, less knee flexion, higher landing velocity, less force absorption, higher GRF, more risk of injury

soft landing characteristics

exert force over longer period of time, more knee flexion, less landing velocity, more force absorption, more muscle groups used, land with lower GRF, less risk of injury