Forces and Motion

Rocket man and the perils of acceleration

Stories from Physics for 11-14 14-16 IOP RESOURCES

The highest empirically recorded acceleration survived by a human was experienced by the test pilot John Stapp while strapped to a rocket sled that could produce just under 180 kN of thrust. He experienced a peak acceleration of 42.6 g and one second of acceleration at 25 g. In five seconds, he reached 1020 km/hr and was then decelerated in just 1.4 seconds. He suffered temporary blindness from burst blood vessels in his eyes, cracked ribs, broken wrists and damage to his circulatory and respiratory systems.

A paper analysing survival rates from falls reports the case of a woman who fell six storeys, and though it is estimated she experienced a deceleration of 140g, she suffered no significant injuries. The sudden jolt caused by opening a parachute can lead to decelerations between 9

  • 12 g and can cause neck pain in skydivers. British standards for vibration exposure in vehicles suggest that accelerations over 0.32 m/s 2 may be mildly uncomfortable and acceleration greater than 2 m/s 2 extremely uncomfortable. A roller coaster fans’ website lists the highest accelerations experienced on roller coasters around the world:
  • AccelerationRoller coaster
    6.3 gTower of Terror, Gold Reef City, Johannesburg, South Africa
    5.9 gShockwave, Six Flags over Texas, Arlington, Texas
    5.5 gDetonator, Thorpe Park, Surrey, UK

    Though humans struggle to tolerate high accelerations, researchers in Japan have discovered bacteria can be successfully cultivated in an ultracentrifuge at accelerations over 400,000 g. Carnivorous aquatic bladderworts use a suction trap mechanism to capture prey; the fluid accelerated by the mechanism can reach a peak acceleration of 600 g. However, this acceleration is dwarfed by the abilities of fungi that live on herbivore dung. Ascomycota and zygomycota use fluid-filled stalks, like squirt guns, to accelerate spores up to 180,000 g. In the animal world, mantis shrimp appendages have been recorded as reaching accelerations of up to 104,000 m/s 2.


    appears in the relation F=ma a=dv/dt a=-(w^2)x
    is used in analyses relating to Terminal Velocity
    can be represented by Motion Graphs
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