Ch.10 Linear Kinematics of Human Movement PDF

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Dr. Nathaniel Ordway...

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Ch.10: Linear Kinematics of Human Movement Monday, February 22nd, 2021 ●

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Review: how do we define kinematics? ○ The pattern of sequencing of movement with respect to time ○ Visually observable ■ Qualitative ○ Measurable ■ Quantitative ■ Displacement, velocity, acceleration What is linear displacement? ○ Change in location ○ Directed distance from initial to final location ○ The vector equivalent of linear distance ○ Measured in units of cm, m, km ○ Ex: the distance a skater travels may be measured from the track left on the ice (did not travel in a straight line) → can determine displacement in a straight line from start to finish ■ The displacement is different than the distance traveled ● Displacement = vector quantity ● Distance = scalar quantity What is linear speed? ○ = distance covered over the time taken ○ = distance / time ○ Scalar quantity ○ m/s (units) What is linear velocity? ○ The rate of change in location ○ = displacement / time ■ V = (d2 - d1)/t ○ The vector equivalent of linear speed ○ m/s (units) ○ The velocity of a swimmer in a river is the vector sum of the velocities of swimmer and current What is acceleration ○ The rate of change in linear velocity ○ = change in velocity / time ■ A = v2 - v 1 / t 2 ○ m/s (units) ○ May be positive, negative, or equal to zero, based on the direction of motion and the direction of the change in velocity ○ Negative acceleration ■ Ex: baseball player sliding into a base involves negative acceleration of

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the base runner (should be, but not always the case) What is a projectile ○ An object projected into the air ○ No additional force generation ○ Ex: basketball, discus ○ Analyzed based on 2 components: ■ Vertical ■ Horizontal ○ Can be analyzed with equations ○ Ex: the human body becomes a projectile during the airborne phase of a jump ○ Why do we analyze the horizontal and vertical components of projectile motion serpartely? ■ The vertical component is influenced by gravity and the horizontal comment is not not ■ Reference system ○ What is the effect of gravity? ■ The force of gravity produces a constant acceleration of -9.81 m/s2 on bodies near the surface of the earth ○ What is the effect of air resistance? ■ The air can create a force on the projectile ○ Ex: ■ 2 baseballs, one dropped and one projected horizontally from the same height ● Both land at the same time since gravity affects their vertical velocities equally ● When projected horizontally, the ball travels further, but they have land at the same time ○ The pattern of change in the vertical velocity of a projectile is symmetrical about the apex ■ Vertical velocity decreases as the ball rises and increases as the ball falls due o the influence of gravitational force Factors influencing projectile trajectory ○ Projection angle = the direction of the projection with respect to the horizontal ○ Projection speed - magnitude ○ Relative height of a projection - initial height relative to landing ■ The difference between projection height and landing height

Wednesday, February 24th, 2021 ●

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Effect of projectile angle ○ Important in shooting a basketball ■ Common error among novice players is shooting the ball too flat a trajectory Analyzing projectile motion

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Equations ■ V2 = v1 + at ■ D = V1t + ½ at2 ■ V22 = V12 + 2ad ■ These equations may be used to relate linear kinematic quantities whenever acceleration (a) is a constant, unchanging value A= 0 A = -9.81 m/s2 ■ V2 = v1 + at ■ D = V1t + ½ at2 ■ V22 = v12 + 2ad Special cases: ■ If object is dropped, then v1 will drop out ■ If object is at apex of motion, then v2 will drop out Great way to begin to learn kinematics because no additional force generation Breakdown into horizontal and vertical components Forces involved: gravity and air resistance...