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Acceleration Due to Gravity

Understand and state acceleration due to gravity and the value of g

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Jumping Buses

Jumping Buses

Credit: Laura Guerin
Source: CK-12 Foundation
License: CC BY-NC 3.0

The image depicts Evel Knievel jumping over 13 double decker buses as he attempted in 1975 at the Wembley Stadium. Evel Knievel failed the jump and ended up breaking his pelvis. If he had accurately calculated the velocity, launch angle, and launch height of his jump, he would have realize the jump was not physically possible.

Amazing But True!

Credit: Cliff from Arlington, Virginia, USA
Source: commons.wikimedia.org/wiki/File:Evel_Knievel_and_Harley-Davidson_XR-750_at_Madame_Tussaud's_Las_Vegas_cropped.jpg
License: CC BY-NC 3.0

Evel Knievel performed his stunts on this 1972 Harley-Davidson XR-750 [Figure2]

As Evel Knievel sails through the air, he travels in two directions. While heading towards the ramp to jump the buses, he initially has a velocity only in the horizontal direction. When he leaves the ramp, he has a velocity in two directions: along the x-axis towards the buses and along the y-axis that will be defined as perpendicular to the buses. To have a velocity in both the x and y direction great enough to pass the buses, Mr. Knievel and his crew must calculate the change in horizontal velocity due air resistance and acceleration due to gravity.

The relationship between position and velocity along the x and y axis is fundamental to understanding motion. From the motion of particles in an electric field to a space shuttle traveling to the moon, the motion of any body can be broken down into 3 dimensions.

Can You Apply It? 

  1. As Evel Knievel soared through the air, did gravity affect his motion along the x-axis, the y-axis, or both axes?
  2. What would be the optimal angle for someone who wanted to jump any object with a motorcycle, assuming that the landing platform is the same height as the launching platform?
  3. If someone attempted to break one of these record-breaking jumps with a flat ramp (causing the rider to leave the ramp parallel to the ground), would they be successful? If the answer is no, what could be done to make the jump successful without changing the angle of the ramp?

Image Attributions

  1. [1]^ Credit: Laura Guerin; Source: CK-12 Foundation; License: CC BY-NC 3.0
  2. [2]^ Credit: Cliff from Arlington, Virginia, USA; Source: commons.wikimedia.org/wiki/File:Evel_Knievel_and_Harley-Davidson_XR-750_at_Madame_Tussaud's_Las_Vegas_cropped.jpg; License: CC BY-NC 3.0

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