Why does high speed collisions like falling cause more damage?


I’m kinda confused, obviously it’s because there is more force involved in the collision compared to a slow speed collision, but why? It’s just the way the universe works, or what?

In: Physics

There is an equation f=ma, f being force m being the objects mass and a is its acceleration. So the heavier/faster you are the more force is applied when something hits something else

It’s because of momentum which is basically the amount of motion occuring during something that is moving.

You can guess all that from the rule of momentum which is Mass x Velocity. So basically the Velocity is proportional to the momentum and contributes as much as the mass. That’s why even a small rock could cause a bigger injury if thrown from a high place.

Each molecular bond, each structure, everything really has an amount of give before it breaks. Once you cross an energy threshold to break that part, that’s it.

There is more energy in a high speed collision, but the same total amount of structure to handle it. So… more parts of the whole breaks when more energy is involved. That’s pretty much it.

As you said, it really comes down to force. There is an equation that applies here: Force equals mass multiplied by acceleration, or f=ma

This acceleration variable is related to speed, so that variable in the equation changes depending on the speed at the time of impact. Acceleration is the rate of change of speed (so how much something is speeding up or slowing down). Thinking about this with a car hitting a pole might be simplest. Let’s say that the car hits the pole, and then comes to a stop. Imagine this same situation twice, once with the car going fast, and once with it going slow.

You know, conceptually, that the slow speed will cause less damage. This is because there is less force generated by the impact (remember, force equals mass times acceleration).

This makes sense when you look at the equation, f=ma. First you have force, which is what you are trying to solve for here (That’s what causes the damage, more force equals more damage).

Then you have mass, which will stay the same in this thought experiment, since it’s the same car involved.

The thing that changes here when you change the speed of the crash is acceleration. This is because when the car is going fast, it has a greater amount of speed to lose to get to a stop than that same car would when it was going slower. Rephrased, that means the change in speed is greater, which means the acceleration variable is greater.

With math, it makes sense that when you multiply a constant variable (mass) by another one (acceleration), you get a higher result when you multiply it by the bigger version of that variable. Because of this (since f=ma), you have a greater force when there is a higher acceleration variable. As we’ve established, the acceleration variable is higher when the speed is higher- therefore, you have a greater force generated with a higher speed crash.

That’s the math answer at least. Another, maybe simpler way to think about it is by imagining yourself getting hit by a car. The faster the car, the more you’re going to get hurt- you are trying to “absorb” more acceleration to stop the car with your body. The more acceleration something tries to “absorb,” the more likely the force generated by that will cause something to break.

So force definitely is a driving factor, but what you can think of as causing the damage is *energy*. The force of something, when it collided with another object, results in contact energy that is then absorbed by one or both objects. That energy will stress, break, and bend bonds at atomic and macro levels as it goes throughout an object.

More force, more *energy*, more damage.

I’m not a physicist, but that’s my best layman’s explanation.

Energy cannot be created or destroyed, it can just be transformed into different forms. This is just a fundamental way the universe works.

If an object moves fast, someone must have expended energy to get it that fast. This energy (apart from “losses” like friction that were mostly transformed into heat) now resides in the moving object, called kinetic energy. Kinetic energy scales with the square of the velocity, so something moving twice as fast has four times the energy.

If a moving object crashes into something, that kinetic energy has to go somewhere. Some will be transferred to the hit object, causing it to move, but some will be used to cause deformation (and the sound of the crash. Sound is also energy). The more kinetic energy enters the crash, the more deformation happens.

When you fall, you accelerate until you hit the ground.

The higher you go, the longer you fall, you hit the ground faster, and with more force.

Force = mass * acceleration squared