Linear Kinetics bio 3

Newton's 1st Law

Law of inertia, a body remains in current state of motion unless acted upon by an external force

Inertia

tendency of an object to keep current state of motion

Mass =

measure of inertia in linear motion

Newton's second law

law of acceleration, an external force applied to a body causes acceleration.

F=

ma

Direction of a =

direction of force

If F = 0, then

a=0

Newton's Third Law

Law of reaction, for every force, there is an = and opposite reaction

Reaction

same magnitude in opposite direction

Ground reaction force directly ties in which with which of Newton's Laws?

3rd

Ground reaction force

reaction supplied by ground, passive force

Why is ground reaction force important for human motion?

Major external force that accelerates the body, only external force you can voluntarily control

Weight is always

constant and downward

Since weight is dependent on gravity, what is the deal with angular motion

no angular motion from earth

Friction

force acting at area of contact between two surfaces

Source of horizontal GRF

friction

μ

friction coefficient, surface conditions

N

not newton, normal force acting

Friction direction

opposite of motion tendency

F𝒇 =

u x N

Magnitude of Friction force is proportional to

normal reaction force and friction coefficient, u and N

Magnitude of friction _____ exceed your force

cannot

Sliding friction

due to relative motion of surfaces

Rolling friction

due to temporary deformation of surfaces

is sliding or rolling friction stronger

sliding

Static friction

friction force experienced with no motion

max static friction is the _________ ___________ ___ ______ _______

force required to initiate motion

Kinetic friction

Friction force experienced during motion

Force required to maintain motion once initiated

kinetic friction

Acceleration =

Force - friction / mass, delta v / delta t

Force net =

Force - friction, m x a

Friction strategies: example of minimizing friction as resistance

lubrication synovial fluid

Friction strategies: Example of maximizing friction as resistance

cleats to prevent slipping

Momentum =

inertia x velocity

Momentum is the

amount of motion

Momentum is a _____ quantity

vector

Momentum unit

kgm/s

Principle of momentum conservation

if no external force, total momentum remains constant

which of newtons laws pertains to the principle of momentum conservation

law of inertia, 1st

Impulse

accumulated effect of force exertion over a period of time

Impulse =

Average force x delta t

Impulse is a ______ quantity

vector

Impulse unit

Ns

What variable causes change in momentum

impulse

Relationship between momentum and impulse

impulse is change in momentum

How to convert mass to weight

x 9.81

When calculating impulse, you need net force. How do you calculate net force with friction

force - friction

Impulse strategies: giving impulse

maximize impulse by maximizing momentum or elongating elapsed time

Impulse strategies: recieving impulse

reduce impulse force/pressure by increasing area/time

Mechanical work

Accumulated effect of force exertion over a displacement

work =

force x displacement, x cos theta

why * cos theta when calculating work?

only horizontal component used

Unit of mechanical work

Joule or Nm

is 0-90 degrees positive or negative

positive, vectors in same direction

is 90-180 degrees positive or negative

negative, vectors in opposite direction

Concentric contraction and acceleration are _______ work

positive

Eccentric contraction and slow down are ________ work

negative

Mechanical power definitions

Rate of work, intensity of work, rate of energy generation and consumption

Power =

W/delta t, force x velocity x cos theta

Mechanical power unit

Watt, J/s

Mechanical power is a ______ quantity

scalar

Mechanical work is a ______ quantity

scalar

Mechanical energy

Capacity to do mechanical work

Mechanical energy, net energy =

potential e + kinetic e

Potential energy

due to vertical position

Potential energy =

mass x gravity x height

Kinetic energy

Due to motion

Kinetic energy =

1/2 mv^2

Mechanical energy is a _____ quantity

scalar

Mechanical energy unit

J, same as work

Conservation of ME rule

if gravity is the only external force acting on a system, then the mechanical energy is constant

Mechanical work vs energy

work causes changes in the mechanical energy of the system

Work energy relationship

W=delta E = delta Ek + delta Ep

The work energy relationship is similar to the

impulse momentum relationship, i = delta M

Positive work leads to an _____ in energy of the system

increase

Negative work leads to a _________ in energy of the system

decrease