Thus, we can see it was the same incident described in different measures. The average impact force is then simply 2400 ( calculation link)Įxample 2: Using the situation in example 1, but now instead of knowing the depth of the dent, we were lucky enough for the impact to be caught on a high-speed camera and we can measure that it took 0.2 seconds from start to end.
7.5 2 / 0.75 = 90 kN and a maximum impact force of 180 kN. Replacing in the formula we get F avg = 0.5 Then we apply the first equation since we know the deformation distance, which is 75 cm = 0.75 meters. What is the impact force of the car?įirst, we need to convert km/h to m/s, which gives us 27 / 3.6 = 7.5 m/s. The deformation distance is measured at 75cm. A car weighs 2400kg (2.4 tonnes) and is moving with a constant speed of 27 km/h when it hits a light pole head on. Calculation examplesĮxample 1: Car crash force. Results from this impact force calculator should mostly be used as a teaching device and a rough guideline, however some demonstrate that the equations can be used to determine the appropriate force sensor measuring range during impact testing, stating that the "perfect rebound assumption" which is part of the formula performs well at least in the case discussed in the white paper. Certain assumptions regarding spring force and wave propagation, as well as the hardness of the materials involved will hold differently in different situations. The impact formula has decent accuracy, but just as any physical model is just an approximation. Car manufacturers, for example, make cars less sturdy than they can be so they can crumble when excessive force is applied to them, thus increasing the deformation distance and hence the impact duration, which results in lower impact force during a car crash. If one thinks about force on impact in terms of development of safety measures and equipment, then it is immediately obvious that since the body mass is usually constant, the variables one can alter are the speed (hence speed limit laws on most roads) and the collision distance or collision duration, which are usually two sides of the same coin. peak impact force) by multiplying the resulting average impact force by two. The formula can easily be extended to calculate the approximate maximum impact force (a.k.a. The above equation can be used to calculate both impact force of a falling ojbect as well as impact force of a horizontally-moving object such as in a car crash or plane crash. Straightforward transformations of these impact force formulas lead to calculations for the body mass, velocity on impact, collision distance or collision duration, all supported by our force calculator. This formula will output the result in Newtons, assuming your input was in the correct standardized metric units: kilograms, meters, seconds, meters per second. Whereas the second equation is applicable if instead of the collision distance we know the duration of the collision ( t) which is Δt = t 1 - t 0 where t 0 is the first moment in which the bodies connect and t 1 is the moment they reach the end of the deformation process by either denting or bouncing off each other. The formula for impact force expressed in terms of the body's velocity (speed) on impact ( v), its mass ( m), and the collision distance ( d) is the first formula below: For other outputs it is in both standard metric units and imperial ones, with the units automatically being adjusted depending on how big or small the resulting value is. The output if calculating collision force is in Newtons or KN, MN and GN, as well as pound-force (lbf). 
The respective input fields will be hidden or displayed upon selecting what you want to use the calculator for. The impact force calculator can also be used to solve for any of the other values: mass, velocity, impact duration and deformation distance. the depth of the bent on a car bumper following a crash.
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You need to know the body's mass, velocity on impact (can be calculated if you know its acceleration and the duration of its travel time) and either collision duration (from first contact to the end of the collision process) or collision distance, e.g. It can also be used to calculate the force of impact of different kinds of projectiles. For example, it can be used to calculate the impact force of a vehicle (car, truck, train), plane, football, of birds hitting a plane or wind mill, as well as for falling bodies that crash into the ground. This versatile impact force calculator is useful for estimating the impact forces involved in collisions of different kinds.
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