ACTIONREACTION FORCES

1
ACTION/REACTION FORCES

• body segments exert a force
• environment delivers reaction force
• Newtons Third Law
• for every force applied on a body
• that body applies an equal opposite force

2

• T F x FA
• F is board reaction
• FA is d ?
• t is board recoil time

3
Internal Forces External Forces

• within defined body
• body free of support
• muscles contractions change body shape
• c of g positionNOT changed

• outside defined body
• body in contact
• muscle contractions change body position
• c of g position CHANGED

4
Motive Forces Resistive Forces

• cause Motion
• muscle, pull of gravity buoyancy
• concentric contraction
• friction
• fluid lift

• oppose/resist Motion
• muscle, connective tissue
• eccentric contraction
• friction
• fluid drag

5
FORCE and PRESSURE

• Force - push, pull, blow, rub that changes a
  bodys motion or shape
• pressure - amount of force acting over area
• p F direct relationship, p A indirect

6
FRICTION FORCE

• Force created between 2 contacting surfaces
• can be a Motive or a Resistive Force
• texture of surfaces rough more friction
• force pressing together the 2 surfaces
• size of surface area NOT a factor
• high coefficient of friction low slippage

7
CENTRIPETAL FORCE

• Center seeking
• forces rotating body to stay on a circular path
• if Fc is insufficient, body will leave path on a
  tangent

8
ELASTIC FORCE

• Recoil ability
• measure of how quickly reformation follows
  deformation
• coefficient of elasticity square root of
  rebound ht/dropped ht
• high e faster reforming

9
BUOYANCY FORCE

• upward lift Force on a body immersed in a fluid
• Archimedes Principle
• upward buoyant F wt of volume of water
  displaced
• Negative Buoyancy - body wt. greater than the wt.
  of the volume of water displaced

10
POWER

• P Force x velocity
• P Force x distance/time

11
ENERGY the ability to do work

• Kinds of Energy
• 1. chemical
• 2. electrical
• 3. heat
• 4. mechanical

• 3 types of Mechanical E
• 1. Elastic
• 2. Gravity - Potential
• 3. Kinetic