JMU KIN 202 saunders test 2

What is kinetics?

The study of forces that cause or result from motion.

What is kinematics?

The study of the description of motion, including time, displacement, velocity, and acceleration.

What is a vector quantity?

A quantity with both magnitude and direction (e.g., force, velocity, acceleration).

What is a scalar quantity?

A quantity with magnitude only (e.g., mass, speed, energy).

What is Newton's First Law?

An object will remain at rest or in uniform motion unless acted on by an external force (Law of Inertia).

What is Newton's Second Law?

The acceleration of an object is proportional to the net force and inversely proportional to its mass (F = ma).

What is Newton's Third Law?

For every action there is an equal and opposite reaction.

What is force?

A push or pull acting on a body; a vector quantity.

What is the unit of force?

Newton (N).

What is mass?

The amount of matter in a body; scalar quantity.

What is weight?

The gravitational force acting on a mass (W = mg).

What is center of mass (COM)?

The point around which a body's mass is evenly distributed.

What is torque (moment of force)?

A measure of the tendency of a force to rotate an object about an axis.

What is the equation for torque?

Torque = Force × Moment Arm.

What is equilibrium?

When the sum of forces and the sum of torques acting on a body are zero.

What is linear momentum?

Mass × velocity of an object.

What is impulse?

Force × time; causes a change in momentum.

What is the impulse-momentum relationship?

Impulse = Change in momentum.

What is angular momentum?

The rotational analog of linear momentum; moment of inertia × angular velocity.

What is moment of inertia?

A measure of an object's resistance to rotational acceleration, dependent on mass distribution.

What is the law of conservation of momentum?

Total momentum of a system remains constant if no external forces act.

What is work in biomechanics?

Force × displacement in the direction of the force.

What is power?

Work ÷ time; or force × velocity.

What is mechanical energy?

The sum of potential and kinetic energy.

What is potential energy?

Energy due to position (mgh).

What is kinetic energy?

Energy due to motion (½mv²).

What is strain energy?

Energy stored due to deformation (like in a stretched tendon).

What is efficiency?

Work output ÷ energy input.

What is mechanical advantage?

The ratio of output force to input force in a mechanical system.

What is distance?

A scalar measure of how much ground an object has covered.

What is displacement?

A vector measure of change in position (straight line from start to finish).

What is speed?

Distance ÷ time; scalar.

What is velocity?

Displacement ÷ time; vector.

What is acceleration?

The rate of change of velocity over time.

What does negative acceleration mean?

The object is slowing down or accelerating in the opposite direction.

What does zero acceleration mean?

The object is moving at constant velocity (or at rest).

What two variables influence linear momentum?

Mass and velocity.

What is the law of conservation of momentum?

In a closed system, total momentum remains constant if no external forces act.

Based on the LCM, what variables can a baseball batter change to hit a ball farther?

Increase bat speed, increase mass of the bat, or optimize collision angle to increase outgoing velocity.

What is the coefficient of restitution (COR)?

A measure of the elasticity of a collision between two objects.

If a ball has a COR of 0.5 and is dropped from 4 feet, how high will it bounce?

1 foot (0.5² × original height).

What three variables influence angular momentum?

Moment of inertia, angular velocity, and distribution of mass.

How might an athlete alter angular momentum to change performance?

By changing body position to manipulate moment of inertia (e.g., a figure skater pulling arms in to spin faster).

What is ground reaction force (GRF)?

The force exerted by the ground on a body in contact with it.

What is the magnitude and direction of GRF?

Equal in magnitude and opposite in direction to the force the body applies to the ground.

How does GRF differ between walking and running?

Running has greater magnitude and shorter duration GRFs than walking.

How does running mechanics influence GRF placement on the foot?

Heel strikers place GRF at the rearfoot; forefoot runners place it closer to the toes, affecting impact forces.

What two variables influence work?

Force and displacement in the direction of the force.

If work is negative, what does that mean?

The object is moving opposite to the direction of the applied force.

If work equals zero, what does that mean?

The object did not move or displacement is perpendicular to the force.

Define kinetic energy.

Energy due to motion (½mv²).

What two variables influence kinetic energy?

Mass and velocity.

Which variable has a larger influence on kinetic energy?

Velocity, because it is squared.

Define potential energy.

Energy due to position relative to a reference level (mgh).

What three variables influence potential energy?

Mass, gravity, and height.

According to the law of conservation of energy, what happens as an object falls?

It loses potential energy at the same rate it gains kinetic energy.

Define power.

Work ÷ time or Force × velocity.

Give examples of sports where maximal power is critical.

Weightlifting, sprinting, jumping events, throwing.

Give examples of sports where sub-maximal power with high efficiency is critical.

Distance running, cycling, swimming.

Define mechanical efficiency.

Work output ÷ energy input × 100%.

What does it mean if a person is 22% efficient?

Only 22% of their energy is converted to useful mechanical work; 78% is lost as heat.

How is movement economy different from efficiency?

Economy measures energy cost of a given sub-maximal task, while efficiency compares work output to energy input.

Why do we measure movement economy in running instead of efficiency?

Because it's difficult to measure actual mechanical work during running, so we use oxygen cost to estimate economy.

How do changes in leg length, mass, and inertia with age influence stride length and frequency from age 5 to 20?

As leg length and mass increase, stride length increases and stride frequency decreases, improving movement economy in walking and running.

How does this affect movement economy during walking and running?

Longer limbs and more efficient stride patterns reduce the relative energy cost per distance traveled.

Provide other examples of changes in body size/shape/composition with age or between sexes that influence biomechanics.

Increases in muscle mass improve force production; changes in pelvic structure affect gait; changes in body fat distribution affect buoyancy in swimming.

What is a proximal-to-distal sequence?

A movement pattern where larger, proximal segments (trunk, hips) initiate motion, followed by distal segments (arms, hands, implements).

How is proximal-to-distal sequencing used to optimize speed?

It allows transfer of angular momentum from large to small segments, maximizing end-point velocity (e.g., baseball pitching, golf swing, soccer kick).

Why does proximal-to-distal sequencing lead to greater speed and precision?

It creates summation of forces and better timing, leading to efficient transfer of energy through the kinetic chain.

Describe techniques that allow athletes to use stored elastic energy from eccentric contractions.

Pre-stretching muscles (e.g., countermovement in jumps, stretch-shortening cycle) increases force output during the concentric phase.

Give examples of biomechanical alterations elite performers use to achieve higher peak velocities.

Better timing of segmental rotations, optimized joint angles, stiffer tendons for elastic recoil, and improved sequencing.

To improve movement economy or efficiency, do elite athletes recruit less or more muscle mass for sub-maximal activities?

Less muscle mass — they use only what is needed, making movement more economical.

To optimize power, what two variables must an athlete develop?

High force production and high movement velocity.

How does resistance training influence these variables?

It increases maximal force production and shifts the force-velocity curve, allowing more power at faster speeds.

Give examples of sports equipment that can improve performance and explain why.

Aerodynamic cycling helmets reduce drag to increase speed; springy running shoes improve energy return; lighter tennis rackets allow faster swings.

What is drag force?

A resistive force opposite to the direction of motion through a fluid.

What factors influence drag?

Fluid density, object velocity, cross-sectional area, and shape.

In what direction do drag forces act?

Opposite to the object's motion.

What is frictional drag?

Drag caused by friction between the fluid and the surface of the object.

Give sport-specific examples of reducing frictional drag.

Swimmers shaving and wearing tight suits reduce surface roughness, decreasing frictional drag and improving performance.

What is turbulence?

Chaotic fluid flow that increases drag.

What factors influence the size and turbulence of the wake behind an object?

Shape, velocity, and surface roughness.

Give examples of reducing wake turbulence in sports.

Aerodynamic bike helmets and drafting in cycling reduce wake turbulence, lowering drag.

Under what conditions does lift occur?

When fluid flows are unequal on opposite surfaces of an object, creating pressure differences.

How do Bernoulli's and Newton's principles explain lift?

Faster flow on one side creates lower pressure (Bernoulli); fluid deflection creates equal and opposite lift forces (Newton).

What is the Magnus effect?

A lift force generated by the spin of a ball that causes pressure differences around its surface.

How does the Magnus effect occur?

Spin alters air velocity on different sides of the ball, creating pressure differences and resulting in curved flight.

Give sport-specific examples of Magnus effect.

Curving a soccer free kick, topspin in tennis, curveball in baseball.

How does center of mass (COM) change during human movement?

It shifts with limb motion (e.g., raising arms moves COM upward; bending forward moves COM anteriorly).

How can we measure COM?

Reaction board method, segmental analysis, or motion capture systems.