408 Lab 4

408 Lab 4 - EXSC 408L Introduction to Biomechanics Lab 4...

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Introduction to Biomechanics Lab 4 & 5 - Linear & Angular Impulse and Momentum Page 1 of 10 Lab #4 & #5 - Linear and Angular Impulse and Momentum Purpose: The objective of this lab is to understand the linear and angular impulse/momentum relationship. Upon completion of this lab you will: Understand and know how to calculate positive and negative impulse using both the trapezoidal rule in Excel and the grid block method. Understand and know how to calculate moment arms, moments of horizontal and vertical forces, and angular momentum. Be able to plot moment-time curves from a data set. Introduction: Many athletic movements, such as the takeoff of a dive, require athletes to generate both linear and angular impulse. The linear impulse will translate the total body center of mass (TBCM) in the direction of the net linear impulse relative to the TBCM. Similarly, the angular impulse will rotate the TBCM in the direction of the net angular impulse relative to the TBCM. I. IMPULSE Linear impulse represents the effect of a force on a system. It is defined as the net force acting over a specified time period. Linear Impulse = Σ F Δ t = area under force-time curve Figure 1. An example of horizontal reaction force. 1 -1 F y forward direction propulsion impulse backward direction braking impulse changes in braking & propulsion cause a change in momentum constant speed = no impulse or change in mv Propulsive Impulse > Braking Impulse => Increase in velocity Propulsive Impulse < Braking Impulse => Decrease in velocity EXSC 408L Fall ‘08
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Introduction to Biomechanics Lab 4 & 5 - Linear & Angular Impulse and Momentum Page 2 of 10 Angular impulse represents the effect of a moment (force acting at a distance from the TBCM) on a system. It is defined as the moment of force acting over a specified period of time. Angular Impulse = Σ M Δ t = area under moment-time curve Figure 2. Illustration of a moment-time curve. A net positive angular impulse indicates that the system will rotate in a counter clockwise direction. II. MOMENTUM Linear momentum represents the quantity of motion that a body possesses. It is defined as the product of the mass of an object and its velocity. L = m * v where L = linear momentum m = mass v = linear velocity Angular momentum describes the quantity of angular motion. It is defined as the moment of linear momentum. H = I cm * ω where H = angular momentum I cm = moment of inertia about the center of mass ω = angular velocity III. PRINCIPLE OF IMPULSE AND MOMENTUM The principle of impulse and momentum is a useful concept for understanding the cause-effect relationship between kinetics (forces) and kinematics (motion). Newton’s Second Law illustrates the basic relationship that Σ F = ma (cause = effect). From this relationship we are able to substitute and rearrange terms to come up with other useful relationships.
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408 Lab 4 - EXSC 408L Introduction to Biomechanics Lab 4...

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