# Comparing Car Collisions - Force & Momentum

• TrpnBils
In summary, when two identical cars collide head-on at the same speed, the forces experienced by the drivers are the same. However, if one of the cars hits a wall instead, the driver will experience twice the force. This is because what hurts you in a car crash is the change in velocity, and hitting a wall brings the car to a complete stop while hitting another car only brings it to a stop relative to the other car. This was demonstrated on Mythbusters.
TrpnBils
Hi - I got into a debate with a friend of mine today and was wondering if you could shed some light on this topic.

Two identical cars are moving at, say, 30 mph and hit head-on. There is some force and momentum involved there...

Would they hit with the same force and/or momentum as an identical car hitting a brick wall at 60 mph?

Assuming there is no elasticity between the cars, etc and they don't bounce off of the wall or other car...

A good question! The answer is actually "no"!

I know it seems counter-intuitive. Your instincts are telling you that because the relative speeds are the same, the impacts should be the same, but this isn't quite the case.
What hurts you when you get in a car crash has to do with how quickly you accelerate to 0 mph. For simplicity's sake, we'll assume the wall is immovable, i.e. it's momentum doesn't change after the collision (which violates the conservation of momentum, but doesn't change the answer). The only thing that matters is the change in velocity during the collision (assuming both collisions take the same amount of time).

If you hit another (identical) car head on, going at the same speed, the final velocities of both cars will be zero.
If that same car is going that same speed, but hits a wall instead, the car's final velocity will also be zero.

If both collisions take the same amount of time, and all three cars involved are going the at the same initial velocity, then the forces experienced by the drivers are identical.

So, going back to your example, the driver of the 60 mph car would in fact feel twice the force that either driver of the 30 mph cars did.You don't have to take my word for it. If I remember correctly, the Mythbusters showed this.

## 1. What is the difference between force and momentum in car collisions?

Force and momentum are both measures of an object's motion during a car collision. Force is the push or pull that an object experiences, while momentum is the product of an object's mass and velocity. In a car collision, force refers to the impact or contact force between two vehicles, while momentum refers to the total amount of motion that both vehicles have before and after the collision.

## 2. How are force and momentum related in car collisions?

In car collisions, force and momentum are directly proportional to each other. This means that as the force of the collision increases, the momentum of the vehicles also increases. This relationship is described by Newton's Second Law of Motion, which states that the force applied to an object is equal to the object's mass multiplied by its acceleration.

## 3. Why is understanding force and momentum important in car collisions?

Understanding force and momentum in car collisions is important for several reasons. Firstly, it allows scientists to analyze the impact of a car collision and determine the severity of the crash. Additionally, it helps engineers design safer vehicles by considering the force and momentum involved in different types of collisions. Finally, understanding force and momentum can also aid in accident reconstruction and determining fault in car accidents.

## 4. How do factors like mass and velocity affect force and momentum in car collisions?

Mass and velocity are two of the main factors that affect force and momentum in car collisions. As the mass of a vehicle increases, so does its momentum, meaning that a heavier vehicle will have more force in a collision than a lighter one. Similarly, a vehicle traveling at a higher velocity will have more momentum and therefore more force in a collision compared to a vehicle traveling at a lower velocity.

## 5. Are there any other factors that can impact force and momentum in car collisions?

Yes, there are other factors that can impact force and momentum in car collisions. These include the angle of impact, the type of collision (head-on, rear-end, etc.), and the type and condition of the vehicles involved (such as the presence of safety features like airbags). Additionally, external factors such as road conditions, weather, and the presence of obstacles can also affect the force and momentum of a car collision.

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