Conservation of Momentum & Energy

Conservation of Momentum & Energy

Both KE and PE can be measured in joules or Nm.

Kinetic Energy

What Caused the Columbia Disaster?

The Columbia Space Shuttle, STS-107 (Space Transport System 107) and its seven crew members were lost when a piece of insulating foam broke off the vehicle during launch, striking the Shuttle’s wing. This damaged the thermal protection tiles, causing the wing to overheat and come apart 15 days later during re-entry. How could a simple piece of very light foam cause this tragedy?

At the moment of impact, the Shuttle and foam were traveling at a velocity of 701 m/s. It was determined that the foam (weighing 0.757 kg) hit the Shuttle’s left wing with an impact velocity of 236 m/s. This was due to the velocity difference created by atmospheric drag on the foam after it separated from the Shuttle. The kinetic energy of the foam upon impact was:

KE = ½ mv2 = ½ (0.757 kg) x (236 m/s)2

= 21,081 joules of energy

STS 107 Mission Patch

Try It!

Since you have no way of knowing if this is a lot or a little, let’s compare 21.1 kilojoules to the kinetic energy of a sledge hammer. How fast would a sledge hammer of say 12 lbs have to be traveling to have an equivalent impact KE? A 12 lb sledge hammer has a mass of about 5.4 kg.

m/s

We know that KE = 21,081 joules.

So KE = ½ mv2 = 21,081 j

And the mass of the sledgehammer is 5.4 kg,

½ * (5.4 kg)v2 = 21,081 j

v2 = (2 x 21,081 j)/5.45 kg = 7,736

v = 88 m/s – very fast, so it would hurt a lot if it hit your toe!