# Will Smart Car Protect you in a High-Speed Accident?

#### jpelletero

Good day,

I'm curious about the Smart Car's commercial. It says it can withstand up to 3 tons of weight.

Now, I want to know if it can protect the passengers in it if a vehicle weighing 1 ton running at 150 kph crash into it?

May I know what's the formula to answer my question?

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#### Drakkith

Staff Emeritus
2018 Award
It's hard to say. The ability to protect someone in a crash is based on a great number of factors, not just the strength of the frame.

The simplest way to put it is that the longer the vehicle can make the impact last, the less harm it does to you. (It will make sense in a moment.) Consider the equation F=MA. This relates force applied to an object, to the mass of an object times it's acceleration. So in an accident, the LESS the acceleration (or deceleration, as it is actually negative acceleration) the less the force is.

Consider a vehicle impacting a solid concrete wall that is very thick and doesn't give at all. The vehicle, and anyone inside it, will go from their initial velocity to zero velocity in a VERY short amount of time, which means that the acceleration is VERY high. As the equation above tells us, a high acceleration means a high force. This is bad.

Now, consider a car impacting a wall made of, say, jello. Jello gives fairly easily, so the car would have a low acceleration, meaning a low force is applied by the wall. It takes longer to stop the car, but it is more gentle, making it much safer.

There are many different safety features designed to prolong the application of the force and reduce the acceleration of the occupants. (As a high acceleration is actually what kills people, IE your skull quickly decelerating as it impacts part of the vehicle and your brain squishing against it) Some of these features are safety belts, airbags, collapsible steering columns, etc. However one of the major factors is point of collision. Impacting head on with something is easier to survive than being hit from the side at the same speed, as there is much more room for the car to buckle and collapse and spread the force out, increasing the time it takes to stop the vehicle and reducing the acceleration. Also, being in a large, heavy vehicle is inherently safer than a small lightweight one, all other factors being equal.

Honestly I think there are too many factors to consider and too many unknowns to be able to reliably answer your question. It appears to me that they have put effort into making the vehicle as safe as possible, but in the end it's still up to you to decide what you want to do. Have you looked for any safety ratings for the vehicle yet? Those would probably be a much better way of answering your question than trying to figure it all out here.

#### jpelletero

It's hard to say. The ability to protect someone in a crash is based on a great number of factors, not just the strength of the frame.

The simplest way to put it is that the longer the vehicle can make the impact last, the less harm it does to you. (It will make sense in a moment.) Consider the equation F=MA. This relates force applied to an object, to the mass of an object times it's acceleration. So in an accident, the LESS the acceleration (or deceleration, as it is actually negative acceleration) the less the force is.

Consider a vehicle impacting a solid concrete wall that is very thick and doesn't give at all. The vehicle, and anyone inside it, will go from their initial velocity to zero velocity in a VERY short amount of time, which means that the acceleration is VERY high. As the equation above tells us, a high acceleration means a high force. This is bad.

Now, consider a car impacting a wall made of, say, jello. Jello gives fairly easily, so the car would have a low acceleration, meaning a low force is applied by the wall. It takes longer to stop the car, but it is more gentle, making it much safer.

There are many different safety features designed to prolong the application of the force and reduce the acceleration of the occupants. (As a high acceleration is actually what kills people, IE your skull quickly decelerating as it impacts part of the vehicle and your brain squishing against it) Some of these features are safety belts, airbags, collapsible steering columns, etc. However one of the major factors is point of collision. Impacting head on with something is easier to survive than being hit from the side at the same speed, as there is much more room for the car to buckle and collapse and spread the force out, increasing the time it takes to stop the vehicle and reducing the acceleration. Also, being in a large, heavy vehicle is inherently safer than a small lightweight one, all other factors being equal.

Honestly I think there are too many factors to consider and too many unknowns to be able to reliably answer your question. It appears to me that they have put effort into making the vehicle as safe as possible, but in the end it's still up to you to decide what you want to do. Have you looked for any safety ratings for the vehicle yet? Those would probably be a much better way of answering your question than trying to figure it all out here.
Hi Drakkith,

Thanks for your response. Sorry if my initial question is too broad.

I'm not actually looking to buy one. I'm just curious on how much force can the strength of it's frame withstand if they say that it can withstand a weight of 3 tons.

Thanks again.

#### Drakkith

Staff Emeritus
2018 Award
Hi Drakkith,

Thanks for your response. Sorry if my initial question is too broad.

I'm not actually looking to buy one. I'm just curious on how much force can the strength of it's frame withstand if they say that it can withstand a weight of 3 tons.

Thanks again.
Let's see, 3,000 kg * 9.8 m/s2 is 29,400 newtons of force.

#### sophiecentaur

Gold Member
"A ton of weight" is not necessarily a good measure of protection. Advertisers have to be accurate in what they tell you but it may not be very relevant to survival in an accident. Where can this ton be applied and where can't it?

#### Khashishi

Check the crash test ratings.

#### CWatters

Homework Helper
Gold Member
In a high speed accident it's not the strength of the car that matters. The human body can only withstand limited g forces. Too much and your internal organs are damaged when they hit your ribs.

Essentially in a head on the car has to decelerate from speed (U) to stationary (V=0) in the length of the crumple zone (S). Lets say you have a 1m crumple zone and are doing 150kph. Using the standard equation of motion..

V2=U2 + 2as

V2 = 0

so

a = -U2/2s

Now 150kph = 42m/s

so

a = 422/2 = 882m/s2 = 90g

I believe 46g is considered just about survivable ?

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#### Alkim

That's it. A real smart car should be quicker than humans in predicting dangerous situations. Even so, I am sure that unless it flies it will be impossible to avoid a collision in certain circumstances, due to the limited possibilities for escape. And once a 1 t vehicle crashes into yours at 150 mph, you are dead for sure, no matter how smart your vehicle and you are.

#### d3mm

Alkin, when he said 'smart car' he meant THE smart car (www.smart.com). He said 150 kph and not 150 mph. 150kph is about 95mph. People have survived faster head-on car crashes but obviously it depends on the specificis of the situations.

#### d3mm

I can't tell you if you will live or not, but I can tell you that the smart does have some nice modern safety features and they are CITY CARS (park anywhere!), and by and large, people do not drive around cities at 150 kph.

The car is just not very comfortable at high speeds on long inter-city roads. The wheelbase (EU definition, distance between front and rear axle) is too short, which makes it very bumpy.

#### 2milehi

Only 70 MPH but survival would be highly unlikely.

Last edited by a moderator:

#### CWatters

Homework Helper
Gold Member
It's pretty clear that the bigger the crumple zone the lower the g force you are subjected to and unfortumately that means big cars with long bonnets/hoods win.

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