Gymnast and Air Bags

Bending the knees upon landing lengthens the impact duration significantly, resulting in significantly smaller F. Do realize that the impulse is not reduced. It is just spread over a longer duration.

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Check out the timers at the bottom left corner. Notice how quickly the car body comes to a rest compared to the passenger. Air-bag or not, the impulses experienced by the the passenger are the same. But hitting the air bag is a lot less forceful than hitting the rigid steering wheel because of the longer impact duration.

“Classic” Perfectly Inelastic Collisions

These are collisions whose outcomes are either obvious or can be calculated mentally.

Notice that,

• • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses travel at a common velocity after the collision.

Perfectly Inelastic “Sitting Duck” Collisions

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Perfectly Inelastic “Jousting” Collisions

“Classic” Elastic Collisions

These are “famous” collisions whose outcomes are either obvious or can be calculated mentally.

(Perfectly) Elastic “Sitting Duck” Collisions

• Notice that,
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses approach and separate from each other at relative speed of u.

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(Perfectly) Elastic “Jousting” Collisions

• Notice that
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses approach and separate from each other at relative speed of 2u.

Cushions and Air Bags

Bending the knees upon landing lengthens the impact duration significantly, resulting in significantly smaller F. Do realize that the impulse is not reduced. It is just spread over a longer duration.

–

Check out the timers at the bottom left corner. Notice how quickly the car body comes to a rest compared to the passenger. Air-bag or not, the impulses experienced by the the passenger are the same. But hitting the air bag is a lot less forceful than hitting the rigid steering wheel because of the longer impact duration.

“Classic” Collisions

Here are a few “famous” collisions whose outcomes are either obvious or can be calculated mentally.

(Perfectly) Elastic “Sitting Duck” Collisions

• For all the above,
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses approach and separate from each other at relative speed of u.

–

Perfectly Inelastic “Sitting Duck” Collisions

• For all the above,
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses travel at a common velocity after the collision.

–

(Perfectly) Elastic “Jousting” Collisions

• For all the above,
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses approach and separate from each other at relative speed of 2u.

–

Perfectly Inelastic “Jousting” Collisions

• For all the above,
  • the total momentum is conserved.
  • when one mass is much larger than the other, the velocity of the heavier mass is hardly changed by the collision.
  • The two masses travel at a common speed after the collision.