study of forces and their effects on living systems
What are the goals of exercise and sport biomechanics?
performance improvement:
technique and training
equipment
injury prevention and rehabilitation:
techniques to reduce injury
equipment designed to reduce injury (braces)
Def of fluid mechanics?
branch of mechanics dealing with the movement of objects through fluids and gases
Important rigid-body mechanics concepts:
a) objects are perfectly rigid
b) best branch for describing and explaining movement
c) statics; rest/constant state/no acceleration
d) dynamics; objects accelerating/decelerating
e) kinematics; decription of motion
f) kinetics; forces and torques that cause changes
g) all of the above
g) all of the above are RIGID-BODY MECHANIC concepts!
Def of statics?
bonus: give an example
the mechanics of objects at rest or in a constand state of motion (no acceleration)
example: sitting, whole body can be static, or can be used just to describe a single body part (i.e. foot)
Def of dynamics?
bonus: give an example
the mechanics of objects that are accelerating or decelerating
example: start of a race
Def of kinematics?
branch of biomechanics concerned with the description of motion
Def of kinetics?
the branch of biomechanics concerned with the forces (and torques) that cause changes in motion
(explains HOW forces and torques CAUSE changes in motion)
Def of Mass?
Units?
quantity of matter making up an object
kilogram (kg)
Def of gravity?
Units?
The attraction of one object to another object
GRAVITY IS NOT A FORCE or AN ACCELERATION!
m/s2
What is weight?
Units?
Weight is the FORCE due to gravity.
WEIGHT IS NOT MEASURED IN KG!
Def of motion?
What are the two things required for motion to occur?
Motion is a change in position
1)time
2)space
What are the 3 types of motion?
1)linear (aka translation) (2 types of translation)
2)angular
3)general
What are the characteristics that make up rectilinear motion/translation?
all points move the same distance at the same time
ALL points move in a STRAIGHT LINE
direction does not change
orientation does not change
described with 1 number/ONE DIMENSION
What are the characteristics that make up curvilinear motion/translation?
all points move the same distance at the same time
the PATHS followed by the points are CURVED
DIRECTION CHANGES
orientation does not change
described with 2 numbers/TWO DIMENSIONS
What are the characteristics that make up angular motion?
(AKA: rotary motion, rotation)
all points on a body move in ircles about the same fixed central line or axis
can occure about an axis withing the body OR OUTSIDE the body
paths are curved
POINTS MOVE DIFFERENT DISTANCES
orientation DOES CHANGE
What is general motion?
What are examples of general motion?
A combo of linear AND angular motions
EX: running and walking
(TRUNK moves LINEARLY)
(ARMS and LEGS move ANGULARLY)
Linear Distance Traveled (ℓ)
The length of the path traveled
Linear displacement (d)
The straight linein a specific direction from initial position to final position.
Displacement is a VECTOR
IF movement is RECTILINEAR/STRIGHT LINE... then distance (ℓ) is the magnitude of displacement!Vectors can be resolved into components!
What is linear kinematics used to describe?
How quickely something changes its linear position
The branch of mechanics that is the best for describing & explaininghuman movement is:
B rigid body mechanics
Fluid mechanics is the study of movement of objects through:
D both A and B
Which of the following is the metric unit for weight and for force:
B Newton
"The mechanics of objects that are accelerating or decelerating" is thedefinition of:
D dynamics
Average velocity is calculated as:
A displacement divided by the time it took for the displacement to occur
If you are slowing down,
B the direction of displacement and acceleration are opposite
Gravity is:
A the attraction of two objects towards each other
Which of the following are characteristics of displacement:
E all of the above
Which of the following statements about force is/are true:
E all of the above
Which of the following factors influences the magnitude of a friction force?
C normal force and coefficient of friction
Which of the following is an external, non-contact force?
C weight
Assuming the normal force does not change, the largest amount of friction would be generated between contact surfaces that are:
D soft and rough
Conservation of momentum "requires" which of the following conditions?
C net external force is z
What happens to momentum when an impulse acts on a system?
D Either A or B
Impulse-Momentum "requires" which of the following conditions?
C There is a net external force
Which of the following statements is/are true about Newton's first law of motion?
D both A and B
Average Linear Speed
Linear distance traveled divided by the time it took to travel that linear distance.
s-=(ℓ)/t
Linear Velocity
RATE of motion in a SPECIFIC DIRECTION, A VECTOR QUANTITY
Average Linear Velocity
Linear DISPLACEMENT of an object divided by time it took for displacement to occur.
v- = d/t
Instantaneous velocity...
same as instantaneous speed except a direction is indicated
If motion is RECTILINEAR, the average speed is the same number as the magnitude of the average linear velocity
UNITS; m/s
Instantaneous linear SPEED is always the magnitude of instantaneous linear VELOCITY!
UNITS; m/s
"ball throw up; linearly decelerates on the way up, and linearly accelerates on the way down"
what does this describe?
Linear acceleration
Mechanical def of linear acceleration
the rate of change in linear velocity
it is a vector quantity
AVERAGE linear acceleration equation in words
What units is AVG linear accel measured in?
change in linear velocity of an object divided by the time it took for the change to occur
a- = ∆V/t = Vf - Vi /t
m/s2
A negative linear velocity indicates:
motion in the negative direction
Motion in the positive direction coupled with positive linear acceleration means:
an increase in the magnitude of velocity, therefore increasing speed
A linear velocity of zero indicates:
no motion at all
Motion in the positive direction coupled with negative linear acceleration means:
a decrease in the magnitude of velocity, therefore decreasing speed
A (non-zero) constant linear velocity means:
speed and direction remain the same
Motion in the negative direction coupled with negative linear acceleration means:
an increase in the magnitude of velocity, therefore increasing speed
Zero linear acceleration can mean:
either no motion or no change in the linear velocity of a moving object
Motion in the negative direction coupled with positive linear acceleration means:
a decrease in the magnitude of velocity, therefore decreasing speed
acceleration can NOT be directly observed!
the direction of motion is not necessarily the same as the direction of linear acceleration
IF YOU ARE SPEEDING UP, YOU LINEAR ACCELERATION IS IN THE DIRECTION OF YOUR LINEAR MOTION
IF YOU ARE SLOWING DOWN, YOU LINEAR ACCELERATION IS IN THE OPPOSITE DIRECTINO OF YOUR LINEAR MOTION
Def of a force:
A push or pull
Cause or change motion
A vector: magnitude, direction, line of action, point of application.
Unit of measurement for a force?
Newtons! (N)
Tensile Force=
pulling or strecthing force directed axially through body
TENDON ON BONE
Compressive Forces=
pressing or squeezing force directed axially through body
BONE TO BONE
Shear forces=
force directed PERPENDICULAR to the forces directed axially through a body
TORN LIGAMENTS TENDONITIS
MOST INJURIES
Weight=
the force that causes two non-touching objects to move towards each other
W=(m)(g)
Mass=
the amount of matter that consitutes and object
Gravity is:
AN ACCELERATION
A VECTOR
Magnitude = -9.81 m/s2
Direction= downward
External forces=
forces that act on an object as a result of its interaction with the environment (can be solid or liquid)
Normal component
force that acts PERPENDICULAR to the surfaces in contact
During running, the force that upward on the runner is the ______________ ______________.
normal component
Parallel component
force that acts parallel to the surfaces in contact.
During running, the force that opposes sliding of the shoe and the ground is the __________ ___________.
Parallel component
Friction force is a contact, external force that results from:
the interaction between the molecules of the surfaces in contact (fluid or dry)
Center of gravity=
an imaginary point in space through which the weight acts on an object
aka; the point of application of WEIGHT!
Dynamic/sliding/kinetic friction=
DRY friction between two surfaces that are moving relative to each other
The greater the normal force, the greater the ___________.
Friction
Why does greater friction develope between soft and rough surfaces?
Because the molecules can interact more easily with a greater coefficient of friction.
Linear kinetics = EXPLAINING the CAUSES of linear motion
Definition of linear kinetics=
study of forces that cause objects to linearly accelerate or decelerate (change in motion)
1st Law = Law of __________
Intertia
what does the 1st law state
an object that is moving will continue to move in the same direction (straight line) with the same velocity/speed
an object at rest will stay at rest
UNLESS it is "compelled to change that state by forces impress upon it"
Linear inertia =
What is the body's linear inertia?
the quantity that RESISTS a change in an object's linear motion.
MASS (m) represents the body's linear inertia
THE GREATER the mass, the GREATER the resistance to change (think of small ball vs. giant ball rolling down a hill... which one is easier to stop?)
WHAT IS THE UNIT OF MEASURE for LINEAR INERTIA!?
kilogram (kg)
Linear momentum (L) =
what is the unit of measure.?
the product of an object's linear inertia and its linear velocity
L = (m)(V)
the faster an object moves linearly, the more linear momentum it has
the larger an object's mass, the more linear momentum it has
kg-m/s kilogram meter per second
what is "quanity of motion" of an object? (aka)
Linear momentum; is way of QUANTIFYING the linear motion and linear inertia of an object TOGETHER into one measure.
In the 1st law, momentum is ___________________.
And the net external force is ______________ . And linear momentum ___________ a ________ __________.
conserved
zero / noneremains a constant value
2nd Law is the law of _____________________.
(what does it say?)
Acceleration.
FORCES CAUSE ACCELERATIONS;
net external forces cause objects to speed up or slow down AND change direction
the object will accelerate in the direction of the net external force
the acceleration will be DIRECTLY proportional to the next external force and INVERSLY proportional to its mass.
2nd law: Linear impulse-momentum relationship!
∑F = ma
∑F t= m ∆v (change in momentum)
∑F t= m (vf - vi) (change in velocity)
Linear impulse measurement unit?
Linear momentum measurement unit?
Newton second (N-s)
kilogram meter per second (kg-m/s)
3rd law=
equal and opposite froce (if not that case.... there is movement)
IN CONTACT; same magnitude applies but in OPPOSITE direction!
