Review Questions - Mechanical Analysis

what is newton’s first law of motion, in both the linear and angular sense?

linear: object stays at rest or constant velocity unless acted on by external force

angular: object stays at rest or constant angular velocity unless acted on by external torque

what is newton’s second law of motion, in both the linear and angular sense?

linear: F =m x a

angular: au = I imes heta

what is newton’s third law of motion, in both the linear and angular sense?

linear: equal and opposite forces

angular: equal and opposite torques

linear impulse is the product of ____ and _____.

force and time

change in impulse is equal to the change in

momentum

how do you standardize or normalize force relative to a person’s body weight? For example, if a person weighs 200 lb, and when they land they produce 400 lbs of force, what is their force in multiples of body weight?

divide force by body weight, 400/200 =2

based on the force/time curves, what are three ways to increase impulse and therefore always increase momentum?

increase force, time, or both

what are some differences between a soft landing and a hard landing? which one has a lower injury risk?

soft: longer time, lower peak force → lower injury risk

hard: short time, high force → higher injury risk

if a person is walking or running, what is the relationship between the braking and propulsive impulse: the person’s velocity is increasing

propulsive > braking

if a person is walking or running, what is the relationship between the braking and propulsive impulse: the person’s velocity is remaining constant

propulsive = braking

if a person is walking or running, what is the relationship between the braking and propulsive impulse: the person’s velocity is decreasing

braking > propulsive

if a person produces a larger ground reaction force during the propulsive phase, what will happen to their final velocity?

more propulsive force → higher final velocity

when a person is absorbing force, such as during the landing or follow through phase, should they try to absorb the force over a shorter or longer period of time in order to reduce injury risk?

absorb force over a longer time

what is the only constant force experienced by the body?

gravity

what are two ways to increase the resistance provided by an elastic band used for rehabilitation or exercise?

stretch band more, use thicker/stronger band

what is the angular equivalent of Newton’s 1st law?

resistance to change in angular motion

a ___ is the turning effect of a force

torque

only the _____ component of a force will cause rotation.

perpendicular

what three factors influence the amount of torque that will be produced?

force magnitude, moment arm length, angle

a positive torque is in the _____ direction, while a negative torque is in the ____ direction

counterclockwise, clockwise

what is the definition of a lever arm and a moment arm? if you use the lever arm, what do you multiply it by to calculate torque? if you use the moment arm, what do you multiply it by to calculate torque?

lever arm: distance → multiply by force

moment arm: perpendicular distance → multiply by force

what is the angular equivalent of Newton’s second law, in equation form?

what happens to angular acceleration if the moment of inertia increases? decreases?

increased inertia = decrease acceleration

decreased inertia = increase acceleration

what happens to angular acceleration if torque increases? decreases?

increased torque = increase acceleration

decreased torque = decrease acceleration

what effect does a propulsive torque and a braking torque have an angular speed/velocity?

propulsive torque → speeds up rotation

braking torque → slows it down

for a first-class lever, what are the arrangements of the components?

FAR

for a first-class lever, which function or functions of a simple machine can this type of lever favor?

can favor force or speed

for a first-class lever, what is an example in the body

neck

for a second-class lever, what are the arrangements of the components?

ARF

for a second-class lever, which function or functions of a simple machine can this type of lever favor?

favors force

for a second-class lever, what is an example in the body?

calf raises

for a third-class lever, what are the arrangements of the components?

RFA

for a third-class lever, which function or functions of a simple machine can this type of lever favor?

favors speed

for a third-class lever, what is an example in the body?

biceps curl

what is the angular equivalent of Newton’s third law?

equal and opposite torques

angular impulse is the product of ____ and ____.

torque and time

to improve performance, we want to maximize ________

angular impulse

to reduce injury risk, we want to decrease the ______

peak torque

isokinetic dynamometers maintain a constant __________ no matter how much torque is applied.

angular velocity

in static equilibrium, both the linear and angular acceleration sum to

zero

to maintain balance, the __________ must remain within the ______

center of mass, base of support

what is the definition of energy?

the state of matter that makes things change or has the potential to make things change

what is the definition of kinetic energy?

the energy that a body has due to its motion

what is the definition of potential energy?

the energy possessed by a body that has the potential to change something but its not currently changing anything

what is the equation for linear kinetic energy?

½ mv²

what is the equation for angular kinetic energy?

½ ​Iω²

what is the equation for gravitational potential energy?

mgh

as an object is moving up, what happens to kinetic and potential energy?

kinetic energy decreases and potential energy increases

as an object is moving down, what happens to kinetic and potential energy?

kinetic energy increases and potential energy decreases

what is the definition and equation for work?

the process of changing the amount of energy in a system, W = F x change in displacement

only force applied in the ____ direction as the movement performs work

same

positive work is associated with a ______ muscle action and negative work is associated with a _________ muscle action

concentric; eccentric

based on our understanding of work and energy, what factors can help a person jump higher

more force, greater distance, better technique

what is the definition of efficiency?

useful output/total input

what is the definition of economy?

energy used at given speed

walking acts like an ____ pendulum, constantly changing energy from potential energy to _____ energy

inverted; kinetic

running is modeled as a _____ on top of a spring

mass

power is the ____ of doing work

rate

what is the equation for power?

P = w/t