Cartões: IB SEHS Topic 10: Friction & Drag, IB SEHS: 4.3 | Quizlet

Friction

Force that acts parallel to the interface of two surfaces that are in contact, and opposes their relative motion.

Force of Friction

Ff = μR

Force of friction = Coefficient of friction x Normal reaction force

Static Friction

the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest

Eg. Friction to keep tennis racket in hand

Dynamic Friction

Frictional force that develops between two surfaces in contact that are moving or sliding relative to each other; sliding friction; kinetic friction.

Eg. Skiing

coefficient of friction

the ratio of the force of friction to the normal force acting between two objects

µ = Ff R

The magnitude of the coefficient of friction

Depends on the roughness of the materials in contact and how hard the surfaces are pressed together and is usually between 0 and 1

Examples of friction in golf

Spikes on the sole of the shoe of the shoe to increase its surface area and dig into the ground and dimples on the ball to create a thin turbulent boundary layer of air that clings to the ball's surface.

Examples of friction in football

Spikes on the sole of the shoe of the shoe to increase its surface area and dig into the ground and laces on the ball.

Examples of friction in ice skating

Narrow sharp edges to reduce surface area and increase pressure in a specific area of contact to encourage melting.

Drag

force acting to oppose the motion of an object through a fluid medium such as air or water.

surface drag

As a body moves through a fluid, its outer surface catches a layer of the fluid nearby, slowing it down compared to the fluid further away and so causing drag

can be minimized by changing the surface to reduce the interaction between surface and fluid

Form drag

As a body pushes against a fluid, the fluid pushes back (action and reaction). By streamlining the body and minimizing the surface area facing the direction of the motion, this type of drag is reduced.

Wave drag

When a body moves along the surface of a fluid (usually water) some fluid is displaced to form a wave. These waves cause additional forces that oppose motion. Wave drag can be reduced by avoiding motion at the interface between air and water.

factors that influence the amount of drag in sports

fluid viscosity

surface size

shape

texture

relative velocity

free body diagram

a diagram showing all the forces acting on an object

Biomechanics

applications of mechanics to the human body and sporting implements, and studies forces on (and caused by) the human body and subsequent result of forces

Kinematics

Kinetics

Kinematics (biomechanics)

study of motion (changle in position) of body or object

linear motion

curvilinear motion

angular (rotational) motion

general motion

linear motion (kinetmatics - biomechanics)

in a straight line

move parts in same distance, direction, and speed

curvilinear motion (kinetmatics - biomechanics)

in a curve

angular (rotational) motion (kinetmatics - biomechanics)

around an axis

body part in circle/rotation, rotates around axis; involves circular/rotational motion/movement

EX: gymnasts doing giants

general motion (kinetmatics - biomechanics)

linear and angular together

Angular+Linear

not everything happens in line/angle

EX: bowling ball and bowling, shot put, javelin, wheel chair athletics, swimming, running

most activities are this

kinetics (biomechanics)

forces involved in the movement of an object/body

liniear kinetics

angular kinetics

linear kinetics (biomechanics)

force, gravity, mass, and weight

angular kinetics (biomechanics)

torque (moments), levers

Scalar quantity and examples

has only magnitude/measurement (pounds, inches, feet squared)

length, area, volume, speed, mass, density, pressure, temp, energy, entropy, work, power, distance

vector quantity and examples

has both magnitude/measurement and direction (mph W)

displacement, direction, velocity, acceleration, momentum, force, lift, drag, thrust, weight

distance (scalar)

how far an object travels, does not depend on direction (d)

Displacement/∆x (vector)

difference between object's starting position and ending

does depend on direction

∆x=final position-initial position

∆x=xfinal-xinitial

in order to define this need directions EX: +/-, N/S/W/E, angles

can be zero if starts and ends at same spot

how far an object has moved in a given direction

velocity

vector

displacement change over time

need direction in answer

=displacment/time

speed with a direction

tells the speed and direction of a moving object

acceleration

vector

change in speed to get up to top speed

tells us the rate speed or direction changes

change in velocity over time

=finalvelocity-initialvelocity/time

in answer time should be squared ex: s^2

momentum

vector

mass of an object x its velocity

whichever has greates velocity if have same mass then will have greater momentum

objects resisteance to want to stop

what four things are related?

momentum, displacment, velocity, and acceleration

Impulse

force appliced over period time to change momentum (change in momentum)

force*time

vector

force in Newtons and time in ms

way to get object to move, result is movement

elite athletes can have more force in less time

had to apply force to get movement going and stopped

product of force and time/the application of force over a period of time (which changes the velocity of body)

area under force-time graph

product of magnitude of torque and its time of application

force, time graph

represents impulse

force is y and time is x

if no force could be air and when putshing foot off ground when running applies force

if negative (footfall) is > postive (push off) are decelerationg

if positive > negative are accelerating

if positive = negative are constant pace

centre of mass

point at which the mass and weight of an object are balanced in all directions

changes with what doing

this could be outside body like in gymnastics

standing up = center

standing on one leg = shifts over to side standing on

raise arms up = shifts up

line of gravity

where body tipped off if go away from this fall because goes with centre of mass

stability

dependent on centre of mass being directly above base of support and 4 other things:

postion of centre of mass

mass of athlete

size of base of support

where line of gravity is

speed

size of linear velocity/velocity

scalar

tell us the rate at which an object moves; how fast are travelling; distance travelled/time taken

motion

change in position measured by distance and time

distance-time graphs

plotting distance againse time can tell you a lot about motion

time always plotted on x-axis, distance plotted on y-axis

If time is increasing but distance does not change, object is at rest/not moving

If an object is moving at a constant speed/time is increasing and distance is increasing constantly with time then object moves at constant speed (is a straight line of graph)

a steeper line indicates a larger distance moved in given time (higher speed

line on graph curving upwards shows an increase in speed/in given time the distance object moves is getting larger (it is accelerating)

tells us how far an object has moved with time

steeper the graph, the faster the motion

horizontal line means the object is not changing its position meaning it is at rest

downard slope means object is returning to the start

speed-time graphs/velocity-time graphs

time plotted on x-axis and speed/velocity plotted on y-axis

straight horizontal like means speed is constant

graph shows increasing speed=acceleration

graph shows decreasing speed=deceration

shows us how the speed of a moving object changes with time

steeper the graph the greater the acceleration

horizontal line means object is moving at a constant speed

downward sloping line means object is slowing down

levers

simple machines that help us apply force

rigid structures, hinged at some part with forces applie at two other points

all levers have three parts: fulcrom, load, effort

3 classes of levers:

1st class

2nd class

3rd class

fulcrom (levers)

the pivot point

load/resistance (levers)

the weight needs to be moved

effort (levers)

force applie to move resistance (or load)

functions of levers

increase the load (or force) that can be moved with a given effort (eg crowbar)

increase the velocity at which an object will move with a given force (eg a golf club)

1st class of levers

the fulcrum lies between the effort and load

EX:

using a hammer to pull out a nail

skull pivoting o atlas vertebrae of spine, with weight of head help by trapeziius and sternocleidomastoid muscles of the neck

2nd class of levers

load lies between fulcrum and point of effort

EX:

running

ball of foot with gawstrocnemius and soleus muscles of calf lifting the weight of body, which is acting through the foot

3rd class of levers

effort lies between load and fulcrum

EX:

fishing with a rod

action of bicep as lifts a load in hand whilst pivoting at the elbow

Newton's First Law

"an object in motion will remain in motion, and an object at rest will remain at rest, unless acted up by an unbalanced force

inertia

Newton's Second Law

net force=mass times acceleration

force is in newtons

mass in kg

acceleration in m/s^2

need greater force to stop large objects with lot mass

lighter objects have greater acceleration

motion

Newton's Third Law

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

EX:

force applied by foot to starting block and block applies force to foot

using blocks propels self more and starting block gets going and gets individual going where want to go

Inertia (Newton's First Law)

resistance of any physical object to change in its state of motion

force

push/pull

acts on an object's perspective, has force exerted on it, requires an agent

vector

to quantify push/pull need to specify both magnitude and a direction

agent (force)

something that acts or exerts power

contact-force

forces that act on an object by touching it at point of contact

long-range force

forces that act on an object without physical contact

base of support/BOS (centre of mass)

location on a body/object where most weight is supported

larger the area the base of support cover more stable will be

line of gravity/LOG (centre of mass)

imaginary vertical line passing through the center of gravity down to a point in base support

what occurs if the LOG falls within the object's BOS? what occurs if the LOG falls outside the object's BOS?

object is relatively stable

object is relatively unstable

what must go outside BOS to initiate/continue movement? direction of what relative to BOS will be the direction of the resulting movement? further away LOG is from what, the greater the tendency body has to move in that direction

line of gravity

line of gravity

base of support

Impulse-momentum relationship

impulse=change in momentum (uses newton's 2nd law)

what still plays key role in angular momentum or anything angular?

centre of mass

moment of Inertia and rotational velocity relationships and how does it work

inverses of eachother

if bring body closer together increases inertia and decreases rotational velocity

if spread body out decreases inertia and increases rotational velocity

what do you add to increase momentum

torque

law of conservation of momentum of linear motion

momentum transfers equally from one object to the other

"in an isolated system, momentum remains constant"

in collision between two objects momentume is conserved (total momentum stays the same)

what is relationship between angular velocity, angular momentum, and moment of interia

if angular velocity is low, moment of interia is high and vice versa

angular momentum=angular velocity x moment of inertia

angular velocity and moment of interia inverses

conservation of angular momentum

Angular momentum is NOT angular speed.

A diver in the air can alter their moment of inertia and their angular speed, but they cannot change their angular momentum until another force is applied to it (hitting the water).

In rotation movements, inertia:

is not only due to mass but how mass is distributed about the axis of rotation.

Projectile motion

related to Newton's 1st law

once force has been removed the object can no longer be altered

path of object determined at moment leaves the hand/raquet etc.

what play a part in how far an object will go?

gravity, air resistance, and lift

Most important factors to affect projectile motion

speed of release/projection speed

angle of release/projection angle

height of release/projection height

if height shorter goes shorter distance, if angle higher then goes father, slower speed goes shorter distance

Bernoulli's Principle

how air pressure works on flying objects (like plane)

high air pressure beneath pushs things up

faster air has lower air pressure

the high air pressure beneath an airplanes wings pushed up to cause lift

airflow velocity and pressure are

inverses

magnus effect

results from a pressure differential created by a spinning body

golf ball, volleyball; rotating ball catches air velocity then drops

stay within are of air resistance and then causes ball to spin due to increased airflow

blow on paper on top then makes it come up

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