Human Movement Exam 3

The principle of conservation of angular momentum?

-when gravity is the only acting external force, angular momentum is conserved -the total angular momentum of a given system remains constant in the absence of external torques

the surface reaction force is used by the dancer to generate ____ during the take off of the tour jete

angular momentum

the arm swing during takeoff contributes significantly to the driver's ____?

angular momentum ex; backflip

What is strain energy?

capacity to do work by virture of a deformed body's return to its original shape SE=1/2kyx2

Turbulent Flow

characterized by mixing of adjacent fluid layers

Laminar Flow

characterized by smooth, parallel layers of fluid

Impact

collision characterized by the exchange of a large force during a small time interval

What are relevant fluid properties?

•density-mass or volume specific weight-weight/volume •viscosity-internal resistance of a fluid to flow

Lift?

-a force acting on a body in a fluid in a direction perpendicular to the fluid flow -coefficient of lift: unitless number that is an index of a body's ability to generate lift

What is Drag?

-a force caused by the dynamic action of a fluid that acts in the direction of the freestream fluid flow -generally a resistance force that tends to slow the motion of a body moving through a fluid

What should competitive swimmers do to minimize wave drag?

-competitive swimmers typically propel themselves underwater -in most swimming pools, the lane lines in are designed to minimize wave action

Law of Acceleration (Newton's 2nd Law)

A force applied to a body causes an acceleration of that body: -of a magnitude proportional to the force -in the direction of the force, -inversely proportional to the body's mass F=ma

What is the law of inertia? (Newtons 1st Law)

a body at rest stays at rest and a body in motion stays in motion, unless acted upon by an external force

What happens in an airborn execution of a spike in volleyball?

a compensatory rotation of the lower extremity offsets the forceful swinging arm so that total body angular momentum is conserved

Buoyancy

a fluid force that always vertically acts upward -Archimedes' principle states that the magnitude of the buoyant force acting on a given body is equal to the weight of the fluid displacement by the body -the point at which the buoyant force acts is the objects center of volume or center of buoyancy

Archimedes' principle

a physical law stating that the buoyant force acting on a body is equal to the weight of the fluid displaced by the body

Angular Law of Inertia

a rotating body will maintain a state of rest or constant rotational motion unless acted on by an external torque that changes the state.

Foil

a shape capable of generating lift in the presence of a fluid flow

What is Fluid?

a substance that flows or continuously deforms when acted on by shear force -both liquids and gases are fluids with similar mechanical behaviors -air and water are fluids that commonly exert forces on the human body

what determines whether a body floats or sinks?

according to the principles of static equilibrium: -floating occurs when the buoyant force is GREATER than or EQUAL to body weight -Sinking occurs when body weight is GREATER than the buoyant force the equation of the sum of the vertical forces must be equal to 0 to float in a motionless position

Law of Gravitation

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

Bernouli principle

an expression of the inverse relationship between relative velocity and relative pressure in a fluid flow -regions of relative low-velocity flow are associated with relative high pressure -relative high-velocity flow associated with relative low pressure

What produces change in Angular Momentum?

angular impulse -change in angular momentum equal to the product of torque and time interval over which the torque acts

Kinetic Friction, Fk

constant-magnitude friction generated between two surfaces in contact during motion

Radius of Gyration

distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics

Potential Energy (PE)

energy by virtue of a body's position or configuration PE=(wt)(h) PE=(mag)(h)

Kinetic Energy (KE)

energy of motion KE=1/2mv^2

Friction

force acting over the area of contact between two surfaces in the direction opposite that of motion or motion tendency -quantified in units of force, Newton -magnitude is the product of the coefficient of friction, and the normal reaction force F=uR

Centripetal force

force direction toward the center of rotation for a body to rotational motion -cyclists and runners lean into a curve to offset the torque created by centripetal force acting on the base of support

What affects changes in Momentum?

impulse: product of a force and the time interval over which the force acts impulse=Ft

The principle of Conservation of Momentum

in the absence of external forces, the total momentum of a give system remains constant M1=M2 (mv)1=(mv)2

The relationship among the impact velocity, temp., and coefficient of restitution?

increases in impact velocity and temp. increase the coefficient of restitution

what factors affect the Magnitude of Wave Drag?

increases with the: -vertical oscillation of the body -increased swimming speed

Factors that affect the magnitude of lift

lift increases with the: -relative velocity of fluid flow -surface area of the flat side of the foil -coefficient of lift -density of the fluid -size, shape, and orientation of the body

Static bodies

magnitude of the friction force is EQUAL to that of an applied force

Dynamic bodies

magnitude of the friction force remains at a CONSTANT level below that of maximum static friction

Maximum Static Friction, Fm

maximum amount of friction that can be generated between two static surfaces

Rolling friction (between a rolling object and a flat surface)

occurs because both the curved and the flat surfaces are slightly deformed during contact influenced by the: -weight, radius, and deformability of the rolling object -coefficient of friction between the tow surfaces

Angular Momentum

quantity of angular motion possessed by a body -measured as the product of moment of inertia and angular velocity as mass or angular velocity increases, angular momentum increases proportionally

Momentum

quantity of motion possessed by a body -measured as the product of a body's mass and its velocity M=mv

Form Drag?

resistance created by a pressure differential between the lead and rear sides of a body moving through a fluid -also known as profile drag and pressure drag

Wave Drag

resistance created by the generation of waves at the interface between two fluids, such as air and water

Skin Friction

resistance derived from friction between adjacent layers of fluid near a body moving through the fluid -also known as surface drag and viscous drag

what is the Magnus force?

results from a pressure differential created by a spinning body

Perfectly Elastic Impact

results in the conservation of the velocity of the system ex; impact of a superball with a hard surface

Perfectly Plastic Impact

results in the total loss of system velocity ex; impact that occurs when modeling clay is dropped on a surface

what factors affect the magnitude of skin friction?

skin friction increases proportionately with the: -increase in the relative velocity of fluid flow -surface area of body over which the flow occurs -roughness of the body surface =viscosity of the fluid

Mechanical Energy

the capacity to do mechanical work -unit of energy is joule, J -there are two forms of energy Kinetic energy Potential energy

Moment of Inertia

the inertial property for rotating bodies representing resistance TO angular acceleration; based on both mass and the distance the mass is distributed from the axis of rotation

Mechanical Work

the product of force applied against a resistance and the displacement of the resistance in the direction of force -W=Fd =unit of work is joule, J

Mechanical Power

the rate of work production -calculated as work divided by the time during which the work was done -unit of power is watt, W

Moment of Inertia pt 2

the sum of the products of each particle's mass, m, and the radius of rotation, r, for that particle squared

The principle of Work and Energy

the work of a force is equal to the change in energy that it produces in the object acted on -where TE is thermal energy, or heat

How would two objects behave following an impact?

this depends on: -their collective momentum -nature of the impact

Coefficient of Restitution, e

unit-less number between 0 and 1 that serves as an index of elasticity for colliding bodies -the closer e is to 1, the more ELASTIC the impact is -the closer e is to 0, the more PLASTIC the impact is

Relative Velocity

velocity of a body with respect to the velocity of something else, such as the surrounding fluid

Law of conservation of mechanical energy

when gravity is the only acting external force, a body's mechanical energy remains constant KE+PE=C -c is constant, that is, a number that remains constant throughout the period of time during which gravity is the only external force acting

What is the Coefficient of Restitution, e, describe?

when two bodies undergo a direct collision, the difference in their velocities immediately after impact is proportional to the difference in their velocities immediately before impact e=relative velocity after impact/relative velocity before impact

what factors affect the Magnitude of form drag?

Increases with -relative velocity of fluid flow -magnitude of pressure gradient between the front and rear ends of the body -size of the surface area of the body perpendicular to the fluid flow

what factors affect lift force?

Fl = lift force Cl = coefficient of lift p = fluid density Ap = the surface area against which lift is generated V = relative velocity with respect to a fluid

Law of Reaction (Newton's 3rd law)

For every action there is an equal and opposite reaction -when one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body.

Angular Law of Reaction

For every angular action, there is an equal and opposite angular reaction

what is the angle of attack?

Angle formed between the primary axis of a body and the direction of the fluid flow

Magnus effect

Deviation in the trajectory of a spinning object toward the direction of spin -results from magnus force