image credit: Insurance Institute For Highway Safety; image source; larger image

Impulse (When Push Comes to Shove)

The idea of the airbag is to increase the time of deceleration of the head and upper body and correspondingly decrease the force required. To learn more, visit Impulse (When Push Comes to Shove).
-- Notice the photo of the steering wheel, bent by the large force that it experienced; imagine the effect of the equal and opposite reaction force on the crash test dummy's head.
-- Check out these crash test videos.

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Physlet Simulations for First-Semester Physics

When a force is applied for particular length of time, it's useful to think about impulse, the product of the force and the time it is applied.
-- Check out the Physlets simulation Physlet Simulations for First-Semester Physics (it's the first one listed under "Momentum").

-- The airbag works by applying a small force for a relatively long time (the opposite of what happens in a head-on crash without the airbag).
-- Ion drive works by applying a tiny force over a very long time.

(This feature was updated on April 22, 2013.)

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image credit: New Millennium Program, JPL, NASA; image source; larger image

Astronomy Picture of the Day: Ion Drive for Deep Space 1

This Astronomy Picture of the Day shows a laboratory test of the ion drive engine that propelled the probe Deep Space 1 to the outer reaches of the solar system.
-- The little solar-powered engine, only about 40 cm on a side, ionized xenon atoms and expelled them at about 100,000 km/s, exerting a small reaction force on the spacecraft over a long period of time.
-- The engine's thrust was small, as was the corresponding acceleration, but since the engine ran for weeks at a time, the final speed was substantial. To find out more about this probe and its unusual engine, visit Astronomy Picture of the Day: Ion Drive for Deep Space 1 and Deep Space 1.

Impulse of Force

To learn more about impulse, visit the Hyperphysics page Impulse of Force.