Kinesiology 3514 Exam 2 Review Flashcards

linear motion

motion in a straight line / translation

scalar

a single number describing the size or amount of something

vector

a number describing a direction and magnitude

linear distance

linear distance traveled (l) is simply the total length of the path traveled by the system of interest

measurements: mm, cm, m, km

linear displacement

linear displacement (d or p) is the change in linear position of the system in a straight line

specified direction from the initial position to the final position of the system

trigonometric relationships - distance (total length)

C = sq rt𝑨𝟐 + 𝑩𝟐

speed

- distance traveled divided by the time it took to travel the distance

- scalar quantity

- speed = distance/change in time (m/s)

a scalar quantity for "how fast an object is moving"

velocity

- the rate of change of displacement

- vector quantity

- velocity = displacement/time (m/s)

a vector quantity for the "rate at which an object changes its position"

acceleration

the rate of change of velocity

- vector quantity

- a = change in velocity/change in time

- units: m/s^2

can an object accelerate with no velocity? how does direction affect acceleration?

yes, an object can have zero velocity and still be accelerating simultaneously

if there is a change in direction, there is a change in acceleration

direction of acceleration

the direction of motion and direction of acceleration is the same when the object is speeding up but the directions are opposite when the object is slowing down

position-time graph

displacement & velocity (=slope), a graph with time data on the horizontal axis and position data on the vertical axis

- displacement

- velocity = slope

- change in distance/change in time

- steeper = higher velocity

- zero slope = zero velocity

velocity-time graph

displacement (=area), velocity , & acceleration (=slope)

displacement - area

velocity - interpolation

acceleration - slope

SEE GRAPH IN LK1

acceleration-time graph

velocity (=area) & acceleration, a graph describing motion of an object, with acceleration on the vertical axis and time on the horizontal axis

displacement - impossible

velocity - area

acceleration - interpolation

only have horizontal lines, you cannot have acceleration that is changing over time

in order for acceleration to be positive, both the direction of acceleration and velocity should be pointing in the same direction and speeding up

kinematics

describes the motion of objects without forces involved, used to describe joint angles

projectile

a body whose motion is subject only to the forces of gravity and fluid resistance (or an object that is launched into the air)

a projectile continues to move due to their own...

inertia (mass)

a projectile is an object through the air that is subjected only to...

acceleration of gravity

the trajectory (or flight path) of a projectile is...

parabolic in shape

law of inertia

Newton's first law of motion - an object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force

projectiles move in 2 dimensions

have both horizontal and vertical components that occur simultaneously but in most cases these components can be worked out individually

horizontal component of projectile motion

horizontal is always in the same direction & length, always constant

why? gravity does not work horizontally to increase or decrease the velocity

v = vf = constant

a = 0

vertical component of projectile motion

always influenced by gravity - motion is changed due to gravity

- always acts downward towards the center of the earth

- creates a constant downward acceleration (g), 9.81 m/s^2

- only affects the vertical component of a projectile's motion

both the magnitude and direction change

combining components

together they produce a parabolic trajectory (path)

3 factors affecting projectile motion

projection angle, projection initial velocity, projection height

projection angle

influences the shape of the trajectory, the angle of release varies according to the activity between 0 and 90 degrees, determines the distance

when initial v and projection height are constant, the projection angle determines the length of the trajectory

projection initial velocity

when projection angle and other factors are constant, projection velocity determines the length of the trajectory (range), max height, time in the air

projection height

- when projection angle and velocity are constant, height determines the time

- greater the relative launch height, longer the flight time, greater the distance

- determines the time a horizontally projected object remains in the air

trigonometry and vector components for calculating projectile motion

vertical velocity: sin theta = opp/hyp

horizontal velocity = cos theta adj/hyp

SEE SL20 in LK2

Equations of Constant Acceleration

vf = vi + at (1)

d = vit + ½ at^2 (2)

vf^2 = vi^2 + 2ad (3)

equations of constant acceleration - range

see slide 21 in lk2

projectile motion practice problems

https://www.scienceflip.com.au/subjects/physics/advancedmechanics/practice3/

law of inertia (newton's 1st)

- if no net external force acts on an object, that object will not move if it was not moving.

- or it will continue moving at constant speed in a straight line if it was already moving.

vertical velocity - law of inertia

law of inertia does not apply - the vertical velocity of the projectile is constantly changing due to the force of gravity.

horizontal velocity - law of inertia

this is a case where newton's 1st law of motion does apply - the horizontal velocity of the projectile is constant, and its acceleration is 0 because no horizontal forces acting on the projectile.

inertia

resistance to a change in motion, directly proportional to mass

propensity for an object to remain in its present state

mass

quantity of matter (units = kg), density = mass/volume, size doesn't completely dictate inertia

law of acceleration

sum of all forces = mass x acceleration

an expression of the interrelationships between force, mass, and acceleration (acceleration is directly proportional to the force) - the observed change in motion is called acceleration

If R > W

feel heavier and the net force acts upward, resulting in an upward acceleration; this is exactly what happens when the elevator speeds up in the upward direction: it accelerates upward and you feel heavier

If R = W

feel neither heavier nor lighter and the net force is zero, resulting in no acceleration

If R < W

feel lighter and the net forces act downward, resulting in a downward acceleration; this is exactly what happens when the elevator slows down: you decelerate upward and you feel lighter

impulse

= force x time

force is NOT applied at an instant but over time

force over time that creates the movements = impulse

momentum

quantity of motion (e.g. large person vs small person are running at the same speed, it's more difficult for the large person to stop their motion; a large person has a large momentum)

= mass x velocity

to stop a system with a large amount of linear momentum, more force is required

impulse - momentum relationship (2nd law)

cause & effort

- force over time that creates the movements

- if the t increase, the F required to change the momentum decreases, because the change in momentum remains the same

change in momentum

- an object has more time to speed up and V is fasted

- product of the mass and the velocity of an object

the application of Impulse results in a change in the Momentum of a body.

law of action & reaction (3rd law)

for every action, there is an equal and opposite reaction; forces always occur in action-reaction pairs

newton's 1st law of motion

a body in motion remains in motion, or a body at rest remains at rest unless a force acts on it

newton's 2nd law of motion

The acceleration of an object depends on the mass of the object and the amount of force applied.

- impulse-momentum relationship

- increasing the duration of force application increases the change in momentum

newton's 3rd law of motion

- forces act in pairs

- for every action, there is an equal and opposite reaction

equilibrium

in all cases, acceleration will be zero

static equilibrium

linear and/or rotational velocities are zero - the body is not moving

dynamic equilibrium

linear and/or rotational velocity is not zero, but is constant

a force is required to...

start, stop or accelerate or alter the direction of linear motion

a torque is required to...

start, stop, reduce, accelerate, or alter the direction of rotational motion

center of gravity

point around which all particles of the body are evenly distributed

only used to denote center of body in vertical direction

center of mass

point around which the mass of the body is evenly distributed in all directions

balance is achieved when CoM lies within the base of support

center of pressure

point of contact through which CoG or CoM acts

braking impulse

negative impulse

propulsive impulse

positive impulse

law of gravitation

all bodies are attracted to each other with a force proportional to the product of the two masses and inversely proportional to the square of the distance between them

F = G(m1m2/r^2)

internal forces

act within defined system (intrinsic)

- i.e. tensile, compressive, shear

- describes the physical interaction between the particles or components within a material

- internal forces can only change the shape of a system

- when an external force is applied, an internal resistance force is created to resist deformation inside the system

external forces

interact with the system from the outside (extrinsic)

- e.g. gravity, normal force, friction, applied force

- only external forces can change the motion of the system

muscles forces are...

internal to the human system, external to the skeletal system

noncontact forces (external)

occur even if objects are not touching each other (gravity, magnetic forces, electrical forces)

contact forces (external)

occur when objects are touching each other

normal force (contact)

perpendicular to the surfaces

- results from two surfaces pressing against each other

- ground reaction force: equal and oppositely directed normal force from earth

friction

parallel to the surface

- when two surfaces slide across each other

friction

force that resists the sliding of 2 objects in contact

- exists whenever two objects are in contact and have the potential to slide across each other

- always parallel to the surfaces in contact

friction is a necessity and a hindrance

- essential force: walk on the ground, stop vehicle on applying brakes

- reduce the efficiency of machines: loss of energy in the form of heat

static friction

occurs when two contacting forces are not currently sliding relative to each other but do possess the potential for movement, keeps an object at rest from moving

dynamic (kinetic) friction

sliding friction and rolling friction, created between any 2 surfaces when they are in a moving position

coefficient of friction

a measure of the amount of friction existing between 2 surfaces

net force (resultant force)

combination of all forces acting on an object, vector quantity

balanced forces

no change in motion, no change in direction, object either at rest or moving at a constant velocity

unbalanced forces

change in motion, change in direction

colinear forces

forces that have the same line of action

coplanar forces

forces are not in the same line but are in the same plane (horizontal and vertical)

coefficient of friction equation

Ff = μFn where μ = coefficient of friction

kinetics

deals with causes of motion and their effects on the motion of objects, when forces act on a body this causes either linear motion or angular motion (net forces cause linear motion/translation)

mass (m)

quantity of matter composing a body, scalar, units are kg

weight (w)

weight is a measure of how the force of gravity acts upon that mass, vector, Fw = mg, units of weight are N

volume

the amount of space that something occupies, units are cubic meter or liter

density

how much matter (mass) is present per unit of volume, mass/volume, units are kg/m^3

concentrated forces

a force acting at a single point

distributed forces

a force that is applied over a distributed area, if an object experiencing a force is deformable, the force may be distributed throughout the object

stress

- N/m^2 or Pa

- vector

- defined as the internal resistive force to the deformation per unit area

pressure

- N/m^2

- scalar

- defined as the compressive force per unit area that is exerted on a surface

principle of conservation of momentum

Total momentum of a system remains the same before and after a collision

- when two objects collide and no other external forces act on them, total momentum of the system remains constant

ELASTIC COLLISION

two objects collide and bounce off each other; total momentum and kinetic energy of the system are conserved

- the momentum of one object is reduced while the momentum of the other object is increased proportionately to keep total momentum of the system constant

inelastic collision

- two separate objects collide and then combine and move together as a single mass

- in a perfectly inelastic collision, the total momentum is conserved but the total kinetic energy is not conserved (IMPORTANT)

- in equations, assign one side a negative value since velocity is vector quantity

elastic collision - momentum in the x-direction (IMPORTANT)

𝑚1𝑣1𝑖 = 𝑚1𝑣1𝑓 COS 𝜃 + 𝑚2𝑣2𝑓 COS𝜙

elastic collision - momentum in the y-direction (IMPORTANT)

0 = 𝑚1𝑣1𝑓 SIN𝜃 + 𝑚2𝑣2𝑓 SIN𝜙

elastic collision equation (IMPORTANT)

m1v1+m2v2=m1v1+m2v2

inelastic collision equation (IMPORTANT)

m₁v₁ + m₂v₂ = (m₁ + m₂) 𝑣𝑓𝑖𝑛𝑎𝑙

coefficient of restitution

proportion of total energy that remains with the colliding objects after the collision (bouncing ball example)

coefficient of restitution formula

e = relative velocity after collision/relative velocity before collision

work

the product of force and the amount of displacement in the direction of that force

work = force x distance

positive work

work is done on an object; applied force on the object is in the same direction as the displacement of the object

negative work

work is done by an object; applied force is in the opposite direction to the displacement

no matter how much physical effort was involved on the part of the person, technically...

no mechanical work was performed if the object wasn't displaced

mechanical work in muscle - isometric contraction

- the muscle remains the same length

- no displacement of muscles' insertions in relation to each other

- NO WORK is performed

mechanical work in muscle - concentric contraction

- the muscle shortens as it contracts

- muscle force acts along the line of muscles' insertions

- POSITIVE WORK is performed