EXSS 385- Linear Kinetics

what is a force?

a push or a pull

what does a force cause?

change in the motion or shape of an object

what is force measured in?

Newtons

what is Newton’s 1st law?

Law of Inertia

explain the law of inertia

a body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state

what is the law of inertia represented by?

Mass

what is mass?

the quantity of matter contained in an object

what is mass measured in?

kilograms

what is a term that mass is often interchangeable with?

weight

what is Newton’s 2nd law?

Law of Acceleration

explain the law of acceleration

a force applied to body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass

what is the big equation tied to Newton’s 2nd law?

F = ma

what is Newton’s 3rd law?

Law of Reaction

explain Newton’s 3rd law

for every action, there is an equal opposite reaction

further explain Newton’s 3rd law

when one body exerts a force on a second, the second body exerts a reaction for that is eqaul in magnitude and opposite in direction of the first body

what is ground reaction force (GRF)?

if one is standing on the ground, one’s COM is pushing downward, and the ground is pushing back up on the purpose with the same amount of force

what is joint reaction force (JRF)?

when a joint is reacting to other forces

what is an example of joint reaction force?

mucles resisting gravity and pulling limbs away/into the joint

what is the 4th law we discussed

Law of Gravitation

what is the law of gravitation?

all bodies are attracted to one another with a force proportional to the produce of the masses and inversely proportional to the square of the distance between them

what is static friction?

friction present when an object is still

how is static friction represent?

F_m

what is kinetic friction?

friction when an object is in motion

how is kinetic friction represented?

F_k

when does the maximum amount of static friction occur?

amount of friction that is there right before the object moves

what is the coefficient of static friction?

what does R represent in static friction formula?

the normal force

what is always going to be less than translational friction?

rolling friction

when thinking about shoe design what coefficient provides sufficient traction?

coefficient less than 0.8

how do you come up with the optimal coefficient?

ration from surface to shoe

what is slip?

coefficient too low and not enough traction

what is trip?

coefficient too high and too much friction can cause injuries because foot stays planted while body tries to move

what are the three stud types for cleats?

• conical studs

• hexagonal studs

• bladed studs

what type of friction is always significantly smaller?

rolling friction

what is rolling friction influenced by?

• coefficient

• normal force

• size of radius

what is translational friction?

friction when sliding along a plane

what is rotational friction?

friction when things roll

what is elastic force given by?

what does the k in elastic force represent?

stiffness

what is stiffness?

explains how stretchy something is; ability to deform and reform

what does the delta s represent in elastic force?

change in length of the structure

what are the four common forces we often discuss?

• gravitational force

• muscle force

• friction force

• elastic force

what is the formula for linear momentum?

M = mv

what are the variables in the momentum equation?

• M = momentum

• m = mass

• v = velocity

what are the units of momentum?

kg * m/s

what is the principle of conservation of momentum?

in the absence of external forces, the total momentum of a given system remains constant

what is impulse?

force that changes momentum

what is the impulse formula?

Impulse = Ft

what is a collision?

two bodies impacting each other

what is perfect elastic?

when objects collide and they bounce off in opposite directions

what is perfect plastic?

when objects collide and they then move together

what represents when something is neither elastic or plastic?

coefficient of restitution

what is work formula?

W = Fd

what are the variables in the Work formula?

• W = work

• F = force

• d = distance

what are the units for work?

joules (J)

what is positive work?

concentric muscle contractions; muscle and motion are happening in the same direction

what is negative work?

eccentric muscle contractions; muscle and motion are happening in the opposite direction

what is the power formula?

P = Fv

what is power essentially?

how much work occurs over a number of time

what are the variables in the power formula?

• P = power

• F = force

• v = velocity

why are we interested in power?

sports purposes; want to generate force quickly and in timely manner; not thinking about simply how much force we can produce

what is mechanical energy?

capacity to do work

what is kinetic energy?

energy during movement

what is potential energy?

how much energy there could be

what is strain energy?

elastic force

what is the formula for kinetic energy?

KE = 1/2mv²

what is the formula for potential enery?

PE = wt(h)

what is the formula for strain energy?

SE = 1/2kx²

what is the conservation of mechanical energy?

when gravity is the only acting force, a body’s mechanical energy remains constant

what is work energy principle?

the work of a force is equal to the change in energy that it produces in the object in which it acts

what does a large change in kinetic energy require?

a large force over a large displacement