Car Crash Calculator – Impact Force (2024)

Our car crash calculator is a tool that you can use to estimate what g-force acts on you in a car crash. Everybody knows that automobile collisions are very dangerous, but what is the physics behind them? Can we predict the consequences of a car crash? The answer is yes and no. The damages to health in an accident can be severe, and they depend on many factors, e.g.:

  • Car speed – the higher the speed, the more energy you have;
  • Seat belt – we will show that seat belts can save your life;
  • Airbag – another thing that can protect your life;
  • Car type – you are more likely to survive a car crash if you're in a bigger car; and
  • Obstacle – the situation is different when we hit a bush or a tree.

We can't precisely calculate whether you will survive or not, but we can make some estimations to be aware of crash consequences. What happens if you drive at a speed of 20mph20\ \mathrm{mph}20mph and you suddenly stop? Just imagine that a 7-tonne block lies on your chest. Yes, it's almost the same. Recently, the NHTSA (National Highway Traffic Safety Administration) performed many crash tests with dummies. Based on these tests, we can make some approximations at what speed you can die in a car crash.

In this car crash calculator, we explain how to calculate the impact force in car crashes and how seat belts and airbags can protect you. You'll find out that they can drastically increase your chances of surviving. You can learn about the force of impact definition and impact force equation in the following text.

You do not need to be the driver to know that you can't stop the car immediately. The total stopping distance depends on the perception time of a driver and the braking distance. The same energy estimated with the kinetic energy calculator will be dispersed much faster on a tree than in water. Thus, hitting trees almost always results in dangerous car crashes.

Force of impact definition – impact force equation

Force of impact is the total force exerted on an object during a collision. To derive the impact force equation, you can consider the law of conservation of energy. In the beginning, a moving object possesses kinetic energy that reduces to zero after the collision (object stops). To fulfill the conservation law, the change of kinetic energy must be compensated by the work done by the impact force. We express it with the below impact force equation

F=mv22d,F = \frac{mv^2}{2d},F=2dmv2,


  • FFF – Average impact force;
  • mmm – Mass of an object;
  • vvv – Initial speed of an object; and
  • ddd – Distance traveled during a collision.

Check the work calculator or work and power calculator to get familiar with work in physics and how it is related to energy.

What may surprise you is that extending the distance moved during the collision reduces the average impact force. It should be easier to understand if we rewrite the above impact force formula in the alternative version using the time of collision ttt instead of the distance ddd:

F=vmtF = \frac{vm}{t}F=tvm

This is a special case of the formula for momentum, described in the impulse and momentum calculator. Now, you can see that extending the time of the collision will decrease the average impact force.

Let's consider two situations where you jump from a specific height. In the first case, you jump to the ground, and in the second, on a trampoline. Because the surface of a trampoline is more stretchy, it extends the time of the collision. You can feel your legs are subjected to a lesser average impact force.

This case is analogical to car crashes. Cars are made to collapse upon impact extending the time of the collision and lessening the impact force. That's why they can't be too durable.

How to calculate impact force? G-force in car crashes

The impact force formulas we used above describe an ideal collision between two objects. In the actual situation of a car crash, the profile of force during the accident can be more extensive – e.g., you should take into account that the car collapses and that a human is not a point mass but a complex body. However, you can still make some estimations of impact force during a car crash.

Take a look at the picture below. At first, the driver sits in the car in constant motion with speed vvv. Then, a car hits the tree and immediately stops. The driver flies forward due to the inertial force until suddenly stopped by the impact on the steering column or windshield. The stopping distance is very short because none of the colliding objects (including the body and, e.g., the windshield) are contractible enough. These are usually dense objects; you can find the density of the most common materials with the density calculator for a comparison. We can estimate the stopping distance to be approximately 4cm4\ \mathrm{cm}4cm in our case (you can change it in the advanced mode of this impact force calculator).

Car Crash Calculator – Impact Force (1)

How to calculate the impact force acting on a driver with a mass of 70kg70\ \mathrm{kg}70kg? Let's use our car crash calculator! If the initial car speed is 30km/h30\ \mathrm{km/h}30km/h and the collision distance is 4cm4\ \mathrm{cm}4cm, then the impact force is about 60kN60\ \mathrm{kN}60kN. It is an equivalence of 6 tons! It is just as if someone put a large stone block on your chest. On the other hand, the stopping time is only 9.6ms9.6\ \mathrm{ms}9.6ms which means that to reduce the driver's velocity from 30km/h30\ \mathrm{km/h}30km/h to zero, the driver has to decelerate almost 89 times faster than Earth's standard gravity g.

How can seat belts and airbags protect you?

The primary task of seat belts and airbags is the same. They both extend the distance of the collision. Assume that we've got the same situation as before. The 70kg70\ \mathrm{kg}70kg driver drives a car with a speed of 30 km/h, but this time, he is firmly held in a seat belt harness. The seat belt will stretch slightly when the impact force is applied. We can say that it can expand by about 20cm20\ \mathrm{cm}20cm (you can change it in the advanced mode of this impact force calculator).

Car Crash Calculator – Impact Force (2)

Again, after using the car crash calculator, you can obtain the average impact force of about 2.5kN2.5\ \mathrm{kN}2.5kN, which is almost 25 times smaller than without the seat belt. It corresponds to a weight of 1.24t1.24\ \mathrm{t}1.24t. The stopping time lengthens to 48ms48\ \mathrm{ms}48ms, and now, the driver decelerates "only" 18 times faster than with Earth's standard gravity g.

To sum up, the seat belt is designed to stop your body from hitting hard things in the car and reduce the impact force you experience by spreading it out over time. The seat belt could occasionally contribute to severe internal injury or even death if the impact force is too big. However, nowadays, seat belts have a mechanism that breaks them at a predefined level of stress. Usually, there are still airbags placed in front of the driver in order to increase their safety.

We have made an example with the driver, but any person in the vehicle is subjected to these dangers. If you crash with a heavy truck, it doesn't matter whether you sit behind the wheel or at the back seat of the car.

Even in low-speed collisions, the impact force which stops your body is in the range of tonnes. You simply won't be able to hold on and prevent injury without fastened seat belts. Moreover, if you sit at the back of the car and you aren't constrained by a seat belt, you will fly straight ahead like a boulder of several tonnes. You will not only hurt yourself but also your friend in front of you!

At what speed can you die in a car crash?

This is one of those questions that doesn't have one unambiguous answer. The heavier the car is, the harder it is to stop it, and the impact force is smaller. On the other hand, the vehicle will immediately stop if it hits a wall of a house, but the situation will be different if it hits another car that participates in traffic. Therefore, we must take into account many different factors.

In general, high speed doesn't produce harmful injuries. What is dangerous for a human is the high acceleration or deceleration given at a specific amount of time. The National Highway Traffic Safety Administration (NHTSA) is an agency that conducts traffic safety research around the world. It describes its mission as Save lives, prevent injuries, reduce vehicle-related crashes. The NHTSA states that "the maximum chest acceleration shall not exceed 60 g for time periods longer than 3 milliseconds" (source: NHTSA).

With our car crash calculator, you have learned that the accelerations during car crashes can be a lot higher than 60 g without fastened seat belts. So use them and save your life! NHTSA states that seat belts reduce death rates by 45% and reduce the risk of injury by 50%.


How do I calculate the forces in a car crash?

To calculate the impact force in a car crash, follow these simple steps:

  1. Measure the velocity at the moment of the impact, v.
  2. Measure the mass of the subject of the collision, m.
  3. Either use:
    • The stopping distance d in the formula: F = mv²/2d; or
    • The stopping time t in: F = mv/t
  4. If you want to measure the g-forces, divide the result by mg, where g = 9.81 m/s².

What is the impact force in a crash at 160 km/h?

Assuming the weight of the driver is 70 kg, we can calculate the impact forces in two situations:

  • Without the seatbelt, the stopping distance would be 4 cm, and the impact force is:
    F = 70 kg × (44.44 m/s)²/(2 × 0.04 m) = 1728 kN
  • With the seatbelt on, the stopping distance increases to 20 cm. The force becomes:
    F = 70 kg × (44.44 m/s)²/(2 × 0.2 m) = 346 kN

Divide F by m × g = 686.7 m/s² to find the deceleration in terms of g. It’s 2517 g without a seatbelt and 504 g with.

Why does wearing a seatbelt increase your safety?

A seatbelt extends the time your body slows down from the speed before the crash to 0. In a car crash, speed is not the only factor that can be dangerous: the stopping time and distance have an even more critical role. A seatbelt keeps you in your seat, only partially expanding, thus distributing the deceleration over a safer time. However, they are not a guarantee: drive safely, always!

How do I find the stopping time in a car crash?

We can find the stopping time from the impact force using the following formula:
t = m × v/F

  • t — The stopping time;
  • m — The weight of the victim;
  • v — The speed of the vehicle; and
  • F — The impact force.

You can find the stopping distance with the simple relationship between time and space:
d = t × v/2

Car Crash Calculator – Impact Force (2024)


How do you calculate the impact force of a car crash? ›

The impact to your body in a crash is called crash force. Crash force is equal to your body weight multiplied by the speed of the vehicle. If you hold your child while riding in a vehicle, you could crush the child during a crash. In a 30 mph crash, a 100 pound adult becomes a 3,000 pound force against the child.

How much force is in a 40 mph crash? ›

person in a 40mph crash if they weren't buckled in: The average impact force is 335,398 N. This would feel like getting hit with a mass of 75,375 lbs.

How much G force is in a car crash? ›

According to GSU's HyperPhysics project, a 160 lb person "wearing a seat belt and travelling at only 30 miles per houra" experiences around 30g of force in a front-end collision with a fixed object. That's 2.4 tonnes of force acting on the body.

What is the formula for impact force? ›

Impact Force from Falling Object

v = m/s. The kinetic energy just before impact is equal to its gravitational potential energy at the height from which it was dropped: K.E. = J. But this alone does not permit us to calculate the force of impact!

Can you survive a 70 mph crash? ›

High Risk of Death: More Than 70 MPH

A motor vehicle traveling over 70 MPH is a fatal car accident near certainty if it crashes with another vehicle or any other object. At that speed, there is almost no time for reactions, very little chance to regain control, and a huge amount of force that few people could survive.

How does a crash at 60 mph compared to a crash at 30 mph? ›

Pedestrian Accidents

If a pedestrian is struck by a car traveling at 20 mph has only a 5% chance of being killed, but a pedestrian struck by a car traveling at 30 mph has a 45% chance of being killed. That risk rises to about 100% at 60 mph.

How much force is 70 mph? ›

Wind Speed and Resulting Force on a Flat Vertical Surface
40 more rows

How much force is 100 mph? ›

Calculating Force: Why Speed Kills

Going 100 mph? 100 x 100 = 10,000. Even though the speed only doubles, the impact force is four times as high at 100 mph as it is at 50 mph.

What is the impact of a crash at 60 mph equal to? ›

Explanation Excessive speeding greatly increases the impact of a crash. If your car hit a solid, stationary object while traveling at 60 mph, it would have the same impact as an object hitting the ground after falling from a 10-story building.

Is it possible to hit 10 g force? ›

While commercial flights exert only very minimal positive and negative G-forces on passengers, several orders of magnitude greater are the G-forces experienced by astronauts, fighter pilots and stunt pilots. These types of pilots can experience brief periods of extreme forces of nine and 10 Gs.

How many G's can a human survive? ›

Normal humans can withstand no more than 9 g's, and even that for only a few seconds. When undergoing an acceleration of 9 g's, your body feels nine times heavier than usual, blood rushes to the feet, and the heart can't pump hard enough to bring this heavier blood to the brain.

What is the highest G force in a car crash? ›

Bräck's crash saw the highest recorded g-forces since the introduction of crash violence recording systems, peaking at 214 g (while death may occur at >50 g). He suffered multiple fractures, breaking his sternum, femur, shattering a vertebra in his spine and crushing his ankles.

What is the average impact force? ›

Average Impact Force Formula

To calculate an average impact force, divide the change in velocity by the change in time times two, then multiply by the mass.

How much force does it take to dent a car? ›

Standards widely known include those published by the American Iron and Steel Institute which defines a minimum dent resistance of 9.7 J and a stiffness that should exceed 45

How much force does a falling person have? ›

Minimizing Fall Forces
Elapsed TimeDistance TraveledForce at Impact
0.251 foot400 lbs.
0.504 feet1,600 lbs.
0.616 feet2,400 lbs.
0.759 feet3,600 lbs.
5 more rows

What speed is fatal in a car crash? ›

When a car is going slowly, the risk of serious injury is about 1%. At 50 mph, the risk increases to 69% for injury and the risk for serious injury increases to 52%. A fatal car accident is practically inevitable at speeds of 70 mph or more.

What speed is a fatal head-on collision? ›

When the cars are going slowly, the risk of serious injury hovers at about 1%. When the speed goes to 50 mph, the risk of injury increases to about 69%, with the risk of severe injuries or fatality going up to 52%. When either car is going 70 miles per hour or more, a fatality or serious injury is almost guaranteed.

What speed do most fatal car accidents occur? ›

A person hit by a car traveling at 35 miles per hour is five times more likely to die than a person hit by a car traveling at 20 miles per hour. The risk of death at every speed is higher for older pedestrians and pedestrians hit by trucks and other large vehicles.

What are the odds of surviving a 70 mph car crash? ›

While getting hit by a car going 15 mph only carries a 1.8% chance of death, getting hit by a car going 70 mph increases the mortality rate to 75.3%. Most people know that driving at high speeds is dangerous, but even they may be surprised that relatively average speeds can result in pedestrian deaths.

Do 80% of all accidents occur at 40 mph or less? ›

More than 80% of all collisions occur less than 40 miles per hour. Most death-causing collisions occur within 25 miles of the victim's home.

How many pounds of pressure is 70 mph? ›

Wind Speed Conversion (MPH)

Ie: if the wind speed is 70 mph, the wind pressure is 0.00256 x 702 = 12.5 psf.

How many pounds of force does a 3000 pound car traveling at 70 mph have? ›

Understanding Vehicle Ejections and Seatbelts

According to Newton's second law of motion, a 3,000-pound vehicle traveling at 70 miles per hour has approximately 15.8 million pounds of forward-moving force to release in the event of a collision.

What does 2.5 G-force feel like? ›

Effects Of G Forces On Pilot:

2.5 G pilots feel heavy limbs. 3G pilots might lose peripheral vision. 3 – 4.5G pilots suffer partial loss of vision.

How much is one g-force in mph? ›

For example: An acceleration of 1 g equates to a rate of change in velocity of approximately 35 kilometres per hour (22 mph) for each second that elapses.

How fast is 10gs of force in mph? ›

How fast is 10G force in mph? G/10 = 3.2 ft/sec/sec = 2.2 MPH per second (3.2*3600/5280=2.2 approximately!) In other words, the speed increases by 2.2 MPH every second.

How much psi is 100 mph wind? ›

q= (V^2)/383.6 where q is the pressure in PSF and V is the velocity in mph. For Example, Speed of 100 mph gives 26.07 PSF. Important Note: This is the wind pressure calculated for the Basic Speed.

What happens if two cars hit at 50 mph? ›

It was proved that the mutual action of two vehicles colliding into the front of each other at the same speed of 50 MPH was the equivalent of 50 MPH of force. Of course, this is an affirmation of Newton's Third Law. Newton's Second Law of motion states that force is equal to mass times acceleration.

What are the chances of surviving a car crash at 80 mph? ›

Going faster than the surrounding traffic has even worse consequences, the same study found: Driving at 80 miles per hour on a road where traffic is moving at 70 increases your chances of a crash by 31%, a crash with an injury by 49 percent, and a fatality by 71%.

Is the force of a 60 mph crash as great as at 30 mph? ›

The faster you go, the less time you have to avoid a hazard or collision. The force of a 60 mph crash is not just twice as great as a 30 mph crash; it's four times as great!

Can a human survive Mach 10? ›

That being said, is it possible for the human body to be able to withstand such acceleration? The most likely answer is a resounding no. Mach 10 speed has never been achieved by a manned aircraft, though, so it has never been tested.

At what speed do you feel G-force? ›

On earth, this is about 9.8 meters per second per second (meters per second squared). Sometimes, this value is used to characterized the gravity-like force experienced by objects or people under high acceleration not caused by gravity.

How much G-force is 80 mph? ›

Assuming that you are traveling in a straight line on a level roadway, you and your car would experience 1G down due to the force of gravity and zero Gs horizontally.

What does 10gs feel like? ›

Kirby often says, “At 10 G's, it's hard to breathe and feels like a house is sitting on your chest.” That's a ton of pressure, literally! When a person begins to lose consciousness due to positive G's, this is called G-lock.

How many G's do astronauts experience on takeoff? ›

The unit g denotes the acceleration due to gravity, where 1 g is the ordinary pull of gravity. Early astronauts were subjected to launch and re-entry forces of up to 6 g or more; in the space shuttle, more than 3 g is experienced on lift-off.

What is 1g of force equal to? ›

A G-force of 1g is equal to the conventional value of gravitational acceleration on Earth which amounts to 9.8 m/s2 (meter per second squared). In other words, it is the force a person (driver, in our case) can experience when they're accelerating or braking.

How many g is a F1 car? ›

G-force in F1 is the amount of force drivers feel due to rapid acceleration during high-speed corners. Sometimes drivers go up to 6G force and they feel force six times their body weight.

What is the peak impact force? ›

Peak Impact is the greatest force seen during the initial landing. This small peak before the main landing is often only seen on Rear Foot Strike landing. Active Peak is the greatest force detected during foot strike.

How much force can the average human exert? ›

There is no realistic limit about the maximum force exerted by the human with the help of devices or machines. Humans can apply force on any object higher than the weight of the body.

What is high force impact? ›

In mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide. Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer period.

What is considered a low impact collision? ›

Low-Impact Collision, Defined

While there is no specific qualifier for what is considered to be a low-impact collision, generally any accident where the cars are traveling less than 10 or 15 mph — and where little damage occurs to the body of the car or passengers — is considered low impact.

How much impact can a front bumper take? ›

In the United States, passenger car bumpers must absorb a five mph impact from another vehicle with no damage to the car body. The foam or plastic make this possible. At impact, that material squishes down between the reinforcing bar and the vehicle's body.

How big of a dent can you pop out? ›

Minor dents with a diameter ranging from 3 to 5 inches can be fixed using PDR. Even the more minor door dents and dings with sizes of 2 inches or less and medium dents of 5 to 10 inches long are possible to repair.

How do you absorb impact when falling? ›

If you are able, a good technique to dissipate the force of a fall is to roll into it. By rolling, you send the energy of the fall into the roll, rather than having your body absorb the impact.

How much force is a 6 foot fall? ›

A person who weighs about 200 pounds and falls just 6 feet will hit the ground with almost 10,000 pounds of force. That's just too much for anyone's grip. Catching yourself during a fall is a Hollywood fantasy. Don't Fall For It!

How do you calculate the probability of a car crash? ›

For every 1000 miles you drive, your chances of getting into a car accident are 1 in 366. The average driver will file an insurance claim for an auto collision once every 17.9 years. This means the average person experiences three to four auto collisions in their lifetime.

How do you calculate the force of a car? ›

The mass of the car is 1500 kg.
  1. Step 1: Acceleration calculation. As per Newton's second law. F = ma. a= acceleration of the car. ...
  2. Step 2: Force calculation. F = ma F = 1500 × 3 F = 4500 Newton. Hence, the force required to impart a car to achieve30 m/s in 10 seconds is 4500 Newton. Suggest Corrections.

What is the formula for calculating collision? ›

What is the formula of collision? From the conservation of momentum, the formula during a collision is given by: m1v1 + m2v2 = m1v'1 + m2v'2. If the collision is perfectly inelastic, the final velocity of the system is determined using v' = (m1v1 + m2v2)/m1 + m2.

How do you calculate collision impulse? ›

The impulse can be calculated by multiplying the average net force (Fave) by the duration of the collision (Δt). (Alternatively, the impulse is equal to the area underneath the force vs. time curve for the collision such as those in the previous example).

What is an example of an impact force? ›

Impact forces acting on falling objects hitting the ground, cars crashing and similar cases. When a crumple zone deforms in a car crash the average impact force is designed to be as constant as possible.

How many newtons of force does a car produce? ›

A car has a mass of 1,200 kg, and an engine that can deliver a force of 6,000 N.

What is the collision rule in physics? ›

Newton's third law of motion is naturally applied to collisions between two objects. In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. Such forces often cause one object to speed up (gain momentum) and the other object to slow down (lose momentum).

What is the difference between impulse and impact force? ›

What is the difference between Impulse and Impact? While impulse is understood in terms of change in momentum of a body and is a function of force applied and the time period for which it is applied, impact force is the force applied over a very short period of time.


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