# – Impact Vs Torque

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Hi all

Why is 500lb of pressure over a short period of time. Such as a few seconds, so much less damaging than 500lb of pressure instantly/impact
Can someone explain

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The 500lbs over a few seconds has the ability to transfer much more energy. Momentum can only be transferred while the objects are in contact (in this scenario).

The speed of the impact defines the amount of force exerted. Force (Newtons) = Mass (KG) X Acceleration (M/S2).

If you hit an object with the same hammer at a a high speed vs slow speed, the acceleration during the impact (or deceleration of the hammer, but it comes to the same thing) is higher. Since the hammer and the object being hit has the same mass in both scenarios, the one with greater acceleration is exerted upon a strong force

Ex:

F = M X A

S1:
F = 5KG X 5m/s2
F = 25N

S2:
F = 5KG X 10m/s2
F = 50N

50N > 25N so the bigger impact (faster speed) exerted a stronger force

Some dynamics can be affected by the rate of change of the force. For instance, our bodies can adapt to quite large forces, but we need time to orient and flex the appropriate muscles, so you can experience something like whiplash if the force changes very quickly and your body is not prepared to absorb the load. This typically applies to systems that are adaptive like animals or machines.

However, I suspect that what you’re asking about is why a 500lb object sitting on something is less damaging than a 500lb object falling on something. The answer to that is that the 500lb object coming to a stop applies much more than 500 lbs of force. It will be 500lb *plus* the force necessary to stop the object, which can be a little bit more, or many times as much, depending on how fast the object was moving and how quickly it comes to a stop.

The amount of damage done in this case will depend on how gradually your surface can bring the object to a halt, and how it absorbs all that energy as it’s being delivered. In the best case you have something like a trampoline or net, which can slow the object down over a long distance, using only a small amount of extra force, and is made of highly elastic material that can handle the extra energy. In the worst case you have a rigid surface that tries to slow down the 500lb mass all at once, experiencing hundreds to thousands of lbs of force and shattering or deforming because it is not elastic enough to store all that extra energy.

Because that’s not how forces work

A 250 kg weight is just pushing downwards with 2500 N of force(gravity is 10 m/s^2 for convenience, yay rounding!) That’s just the block sitting there

Drop it from 10 meters up and it’ll be doing 10 m/s at impact 1 second later. To bring it to zero speed over another 10 meters would take 2500 newtons of force to support it’s weight and another 2500N to decelerate it at the same rate.

Stopping it in a shorter distance requires significantly more force/acceleration to bring it to a stop quicker. More force = more damage

Stopping it in 0.1 meters would take 0.02 seconds requiring 127,500N, and stopping it in 1 mm takes 1,252,500N