chapter 12 linear motion
Page 1: Introduction
Presenter: Tyler Hosey
Institution: University of South Florida
Page 2: Lecture Overview
Focus on aspects of Force:
Magnitude, direction, and point of application
Internal and external forces in the body
Definitions:
Inertia, momentum, and impulse
Relation to Newton’s Laws of Motion
External factors modifying motion:
Weight, friction, elasticity, buoyancy, drag, lift
Definitions of work, power, energy
Analysis of Linear Motion
Page 3: Understanding Force
Definition of force:
A push or pull
Effects of forces:
Produce, stop, prevent motion
Influence one body upon another
Characteristics:
Has both magnitude and direction
Page 4: Force Example
Example:
A barbell exerts 250 N of force
Lifter must apply a force greater than 250 N upwards at the center of gravity
Page 5: Aspects of Force
Force as a vector quantity:
Must identify magnitude, direction, point of application
Page 6: Magnitude of Force
Magnitude defined:
Amount of force applied
Weight definition:
Result of gravity on mass: w = mg
Example:
The 250 N force from the barbell = weight
Page 7: Magnitude of Muscular Force
Factors affecting muscular force:
Number and size of contracting fibers
Muscles act collectively:
Maximum strength measured by dynamometer through anatomical levers
Page 8: Direction of Force
Direction explained:
Along the action line of the force
Gravity direction:
Downward vector from the center of gravity
Muscular force direction:
Direction of the muscle's line of pull
Page 9: Direction of Muscular Force Vector
Muscle angle of pull:
Angle between the line of pull and the mechanical axis of the bone
Page 10: Point of Application
Definition of point of application:
Where force is applied to an object
Gravity's point:
Through the center of gravity
Muscular force point:
Muscle attachment to a bony lever, linking to mechanical axis
Page 11: Nature of Force
Definition:
Push or pull that induces motion changes
Internal forces:
Muscle forces on body structures
External forces:
Outside influences (gravity, air/water resistance, friction)
Page 12: Newton’s Laws of Motion
Three laws explaining object motion:
Law of Inertia
Law of Acceleration
Law of Reaction
Page 13: Law of Inertia
Stipulations:
Object remains at rest or in uniform motion unless acted upon by an unbalanced force
Friction & air resistance affect motion
Inertia definition:
Property keeping object in state of rest/motion
Page 14: Law of Inertia
Summary:
Object stays at rest/motion until unbalanced force acts
Mass and inertia:
Greater mass = greater inertia
Page 15: Law of Acceleration
Definitions:
Acceleration: directly proportional to force and inversely proportional to mass
Equation:
F = ma
Effect of force and mass on acceleration:
More force = more acceleration
More mass = less acceleration
Page 16: Momentum
Definition of momentum:
Net force multiplied by time
Formula:
F = m x a
Increase in momentum:
By increasing mass, velocity, or both
Relation to deceleration:
Harder to decelerate with greater momentum
Page 17: Impulse
Definition of impulse:
Net force multiplied by time, leading to change in momentum
Relation:
F = m x a
Greater force or time increases impulse
Page 18: Law of Reaction
Principle:
For every action, there is an equal and opposite reaction
Page 19: Summation of Forces
Muscle-generated force can be summed from segment to segment
Momentum can be increased or decreased by changes in mass or velocity
Principle of conservation of momentum:
Impulse increases momentum, typically through sequential transfers in movements
Page 20: Factors Modifying Motion
Forces affecting motion:
Weight, Contact Forces, Ground Reaction Force (Newton’s 3rd Law)
Friction, Fluid Forces, Buoyancy, Drag, Lift
Page 21: Weight
Definition:
Measured as the weight of the body through its center of gravity towards the earth
Page 22: Ground Reaction Force
Reaction to action:
Jumper pushes off ground; ground pushes back
Page 23: Friction
Definition:
Opposes attempts to slide/roll
Influence on performance:
Can be increased or decreased based on objectives
Page 24: Friction Details
Characteristics of friction:
Proportional to force pressing surfaces together
Acts parallel to surfaces against motion
Variables include weight and reactive forces
Page 25: Elasticity
Definition:
Object's ability to resist distortion and return to original shape
Stress vs. Strain definitions:
Stress: force on an object
Strain: distortion of the object
Page 26: Buoyancy
Archimedes’ Principle:
Solid immersed in liquid is buoyed up by a force = weight of the displaced liquid
Page 27: Lift and Drag
Fluid resistance concepts:
Can create lift or drag
Importance of boundary layer and object design
Page 28: Work
Definition:
Product of force and distance
Formula:
W = Fs
Common units:
Newton-meters in SI; foot-pound in US system
Page 29: Work Example
Example calculation:
Work done lifting a suitcase against gravity
Horizontal distance is not significant for work calculation
Page 30: Positive & Negative Work
Definitions:
Positive work: done in direction of movement
Negative work: done against direction of movement
Page 31: Power
Definition:
Rate at which work is done
Formulas:
P = Fs / t, P = W / t, P = Fv
Page 32: Energy
Definition:
Capacity to do work
Law of Conservation of Energy:
Total energy in an isolated system remains constant
Page 33: Mechanical Energy
Classifications of mechanical energy:
Potential Energy (PE = mgh)
Kinetic Energy (KE = 1/2 mv²)
Page 34: Analysis of Linear Motion
Principles for analyzing linear motion involve:
Identifying forces like weight, buoyancy, propulsive forces, drag, ground reaction forces, lift, and friction
Page 35: Lecture Review
Overview of key topics:
Aspects of Force, Inertia, Momentum, Impulse, External factors,
Work, Power, Energy
Analysis of Linear Motion
Page 36: Conclusion
End of presentation
University of South Florida.