What is Impact force: Definition and 108 Discussions

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. The effect depends critically on the relative velocity of the bodies to one another.
At normal speeds, during a perfectly inelastic collision, an object struck by a projectile will deform, and this deformation will absorb most or all of the force of the collision. Viewed from a conservation of energy perspective, the kinetic energy of the projectile is changed into heat and sound energy, as a result of the deformations and vibrations induced in the struck object. However, these deformations and vibrations cannot occur instantaneously. A high-velocity collision (an impact) does not provide sufficient time for these deformations and vibrations to occur. Thus, the struck material behaves as if it were more brittle than it would otherwise be, and the majority of the applied force goes into fracturing the material. Or, another way to look at it is that materials actually are more brittle on short time scales than on long time scales: this is related to time-temperature superposition.
Impact resistance decreases with an increase in the modulus of elasticity, which means that stiffer materials will have less impact resistance. Resilient materials will have better impact resistance.
Different materials can behave in quite different ways in impact when compared with static loading conditions. Ductile materials like steel tend to become more brittle at high loading rates, and spalling may occur on the reverse side to the impact if penetration doesn't occur. The way in which the kinetic energy is distributed through the section is also important in determining its response. Projectiles apply a Hertzian contact stress at the point of impact to a solid body, with compression stresses under the point, but with bending loads a short distance away. Since most materials are weaker in tension than compression, this is the zone where cracks tend to form and grow.

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  1. K

    Jackhammer on Vehicle Suspension, Unsprung Mass, Tire patch load

    Hello all, I wanted to know what would happen if I put a jack hammer system on the unsprung part of the suspension, I posted this on the engineering forum but couldn't get a complete answer. https://www.eng-tips.com/viewthread.cfm?qid=512117 Basically the argument was if the reaction would...
  2. B

    Impact force reduction after passing through a medium

    Hello, Please see the attached sketch. A car hits a mass of soil and applies the impact force of F. The force/wave travels the distance L through the mass at the end of which there is a wall so I think the force attenuates. Assume we have all the properties of the mass. My question is, what...
  3. makamo66

    I Board Breaking: Why Strike Center for Good Break?

    I have read that a practitioner of a martial art striking a target of wood or concrete needs to strike as much as possible to the center of a target in order to get good break. What is the physical reason or formula behind this? I'm thinking maybe you don't want to create a torque.
  4. C

    I How to Calculate force exerted on a falling body?

    I'm curious about impact on falling object, so i have taken initiative to solve this problem. I considered only force on the falling object would be its weight and taken F=mg. With only limited data m=.25kg and drop height h=1m. Pondering on this consideration practically, it will have more...
  5. L

    Impact force of model rocket with parachute

    I just launched a 2.2kg model rocket that stands about 5 feet tall and has a airframe that is 4 inches in diameter. I am trying to find how much the impact force is when the rocket hits the ground at 16MPH. Whats the best approach? Momentum? KE? or something else:) thanks
  6. Jun

    How can I calculate the maximum impact force on the helmet?

    I am studying the force that helmets have to withstand. If I drop a 5kg head model and helmet at 1.064m on an anvil and the impact time is 0.005 seconds, how do I get the 'maximum' impact load on the helmet?
  7. L

    B Wanting to do some impact force experiments

    I have 3d printed some 25mm cubes all with the same parameters. what i want to do is take some different weight dumbells, and drop them all from half a meter onto a cube. My goal is to collect data and see at what impact force the cube fails. For me, failure will be when layers break apart, not...
  8. S

    A Motorcycle, the force exerted upon from collision

    Synopsis, The insurance company wants to repair this 3-year-old motorcycle with 3400 miles on the odo father taking this hit. The motorcycle was modified with an aftermarket "engine guard," which was made out of powder-coated steel tubing and bolted directly to the frame which is made out of...
  9. J

    I Momentum, impact force and Earth

    Suppose two objects, A and B, with large lengths LA and LB, and masses MA and MB, collide at time t0. Both objects before collision are vertical and aligned concentrically, being object B positioned initially at a higher z coordinate than object A. The bottom end of object A is rigidly...
  10. FEAnalyst

    Modeling impact forces in rotary motion

    Hi, how can I calculate the impact force in case when some object is in uniform circular motion and then suddenly hits the target. For example consider lawn mower's blade hitting stone or drum woodchipper's blade hitting branch. Both blades are already moving at full speed when they hit the...
  11. J

    Designing Impact Force Test Rig for Material Strength Testing

    Hi all, I have just started work experience at an engineering company in the design department. I've be tasked to develop a test rig, Similar to a charpy rig. Intended to measure the impact strength of materials. The design will consist of an A-frame structure with swing arm attached to the...
  12. M

    How to Measure Impact Force / Energy Absorption

    Hi, I am a bit out of my league here, but had a question. I have 5 pieces of .25" thick foam/padding of different densities, and I wanted to measure which one absorbs the most energy (weakens the impact) when struck by a fist/punch or even a ball, how would I do that? I ran across a...
  13. Y

    Breaking down cellulose using impact force

    Generic biomass such as leaves contain a large amount of total carbohydrates, mostly in the form of cellulose. Some animals such as apes and can digest cellulose and that is how they can survive on leaves. Humans cannot digest cellulose because we lack the enzymes necessary to decompose...
  14. G

    Pendulum Hammer Impact Force Calculation

    Hi all, I'm a bit embarrassed but I'm extremely rusty with a lot of engineering principles. I've mainly been working in automation and controls within a manufacturing setting and have not done anything like this in ages. Anyways, I have a problem I need to solve and I need to determine the...
  15. S

    Impact force calculation due to a rotating object in Overspeed Trip Valve Design

    Bolt comes out by distance d=1.58 mm when speed of rotation of shaft reaches its trip value (w_trip). m is mass of trip weight (Bolt assembly) One of the approach which I had considered is work energy theorem. Initial energy = 0.5m*(w_trip*(r+d))^2 Final Energy= 0.5m*(w_trip*r)^2 (Assuming bolt...
  16. Emilyyyyyyyyy

    Calculate the impact force when falling from a height

    To find vx vx = dx/t = 3.86 m/1.5 s= 2.573 m/s To find Ek Ek = ½mvx²= ½(79.4)(2.573)²= 262.8 J W = FnetΔd Fnet = 262.8 J/ 3.86 m = 68 N He hits him with a force of 68N
  17. FEAnalyst

    Impact force in the Charpy test

    Hi, could you tell me how to calculate approximate value of impact force during Charpy test (pendulum hitting sample) ? The only formulas that can be found in literature for this test are maximum velocity ##v=\sqrt{2gh}## and work done for fracture ##K=mgR(cos \beta - cos \alpha)##. But it...
  18. L

    Impact force -- Airsoft versus paintball pellets

    Ok, here is a small back story: I love both airsoft and paintball. Airsoft, for those who may not know what it is, is a sport where you shoot 6mm plastic bbs at each other. The bbs have differnt masses to them.. .20g, .25g .28, and .32 are common masses. When i first started last year, i was...
  19. J

    What challenges arise when developing a .490 caliber impact munitions weapon?

    My name is John Hayes, I am the owner/inventor of the Hayes Less Lethal hand held, .490 caliber, impact munitions weapon (hayeslesslethal.com). I have been working hard at this project for 10 years, have 5 issued patents 4 US, and 1 Foreign. I have no Physics background but, for obvious reasons...
  20. C

    B How do I calculate the Impact Force of an object?

    Okay so as you may have already guessed I'm really new to this site (as in I made my account about 2 minutes ago) and I'm really, really bad at maths so I need a lot of help with this question. I'm not even sure if this in the right sub-forum but if it isn't please relocate it to the correct...
  21. B

    Ceiling fan and impact force on the blades

    A ceiling fan has kinetic Momentum in 1 blade hitting a fixed target. Would the design allow the other blades to flex , reducing target impact? If the 4 blades are combined and bolted together at same velocity is different Momentum delivered? Similar q : a human arm is about 8kg and a sword...
  22. G

    Impact force from rotating object?

    Hi, Please could someone help me with the following, I have a rotating cutter and I need to calculate the impact force on an inspection window if one of the cutter blades was to separate from the main assembly. The cutter is spinning at 3000rpm The cutter radius is 115mm (rotating radius)...
  23. S

    What was the impact force of a 30 mph collision on my Scion xB?

    Hello! I have a question and I was wondering if you guys could help and please let me know if this is totally the wrong place to be writing on. I need to calculate the force on a collision I was in. I have a Scion xB 2006 that weighs between 2360 lb to 2600 lbs. The other car is a Ford...
  24. G

    Retarding impact force when object impacts stationary object

    Homework Statement in a metal stamping machine, the upper die block has a mass of 35kg and falls from a height of 2m on to a fixed metal block. if the depth of indentation is found to be 10mm, find the average stamping force assuming the upper die block does not rebound. force=work/distance ...
  25. J

    Impact Force of a Horizontal Moving Projectile

    What is the correct way to calculate the impact force of a 2"x4" flying through the air and hitting a solid cross beam? The knowns are: Velocity: 50 ft/sec Distance To cross beam: 12 ft 2" x 4" Weight: 9 lbs I don't know much the cross beam will deflect on impact, so the stopping distance is...
  26. D

    How to measure the impact force of a moving object

    So I have been researching, I'm no genius, on how to measure the force of a moving object. Now I have seen some of the equations and Newtons law and all but what I am specifically trying to do is figure out the impact force of an arrow. eventually this will be calculated into how much force of...
  27. H

    How Can You Calculate the Impact Force of a Falling Egg?

    I searched engineering calculators and they rely on the input you know the stopping time or the stopping distance - easy for a car but not an egg. Knowing either of these quantities makes the problem trivial, but how to estimate or calculate them?? What is the best assumption for either and...
  28. VNV

    How can you negate impact force?

    In my science fiction universe, I have a small technology called a 'Kinetic Absorption Module'. It's not mentioned very often, but it's a key component of my supersoldiers' armor. How it works is it acts like a shock absorber, but within a small, one inch long by one and a half inch wide...
  29. Lily May

    How to work out this impact force

    Homework Statement During a Formula 1 race a car that was traveling at a speed of 172.8 km/h crashed into a wall. When the car hit the wall it came to a complete stop in 0.0272 s. If the driver of the car holds a mass of 70kg, calculate the impact force he experienced. Homework Equations I...
  30. J

    Equivalent Bending Moment due to Impact Formula?

    Hi guys and girls, I've been working on this problem for a little while now but I'm not really getting the result that I want. This is what I have: I have what is essentially a big pair of vice grips controlled by a hydraulic cylinder. The cylinder opens and closes both arms of the vice grips...
  31. L

    Need Help Finding Cheap and Suitable Impact Force Sensor

    Hi there, I'm new to PhysicsForums, But I need some help finding an impact force sensor that would suit my needs, and I'm pretty new to this so please be patient with me. (Yes, I've tried google, but I am not great at looking for things) Any help would be sooooo extremely appreciated -It...
  32. D

    Calculating Impact Force When Force Is Not Constant

    If force isn't constant in a system, how can I calculate impact force of two bodies accelerating towards each other. Can I use the Work formula since energy in a system is conserved? Give an example, of a way I can calculate impact force in a system in which force is not constant. Thanks.
  33. M

    Impact force during lowering of a load

    Homework Statement An offshore crane is lowering a load with a constant speed of 0.2 m/s. The crane tip has a maximum vertical and horizontal acceleration, as a result of a seastate, of 2.0 m/s2 (vertical) and 0.8 m/s2. The crane needs to lower a 200 ton object onto a stationary object. The...
  34. A

    Impact force of falling object

    Homework Statement I am doing a project on pressure sensitive films and finding if they indicate the correct amount of impact. I have carried out an impact test by dropping a mass of 5KG from a height of 1m. I have calculated the velocity to be 4.43m/s. The kinetic energy just before impact is...
  35. normal_force

    Impact force of Rigid objects and no displacement

    I was wondering something, I dropped a box onto my glass desk but it didn't bounce back, I also hit a hammer against a rigid wall, the matter smacked into the wall, it has KE. It never bounced back, I didn't see any deformation or rebound in either situation, I wasn't hitting too hard nor...
  36. E

    Impact force of pressure fired vessel (Help needed)

    Ok folks I have a down hole oil tool which seals a well bore. it weighs 63KG (139 lbs) I have worked out that it is being loaded up from above with 53879 lbs. by applied pressure/ hydrostatic pressure if it was to instantly release and drop 7m what would the impact force be on a restriction...
  37. Junichirol

    Calculating impact force during landing of aircraft

    I'm having my degree FYP with the title of 'water landing: conceptual design of float component of seaplane upon touchdown'. 1. ) I need guideline for calculating impact force of the seaplane when it touchdown on the water surface. 2. ) Regarding the landing time and landing distance. I'm...
  38. David McArthur

    Comparing force of static object to that of an impact force

    I have been asked by a piling engineer to try to come up with an alternative to static pile testing in a restricted access site. Normally a pile test is carried out by applying a static load to the ground and measuring the deflection of the pile under the load. This of course requires a large...
  39. R

    What was the impact force of the car that hit me while riding my bike in 1989?

    Hello physics forum, thanks for the welcome. I was knocked off my push bike in 1989. The police officer who was driving a toyota corolla that weighs 880kg. He claims to have struck me on the right side of my body at 40 km. Doctors say that not possible as 95% of injuries were on the left. 2...
  40. S

    Solving Impact Force Equation: Tips & Explanations

    Hello, I have been turning to this subject and tried to develop the right equation on my own. What I did was: mgh = ½kx2 (fall energy = spring energy) x2 = 2mgh/k (obviously devided by ½k) sqrt(2mgh/k) = x (taking out square root) F = mgh/x = mgh/sqrt(2mgh/k) = sqrt(½mghk) (energy /distance...
  41. K

    Calculating Impact Forces on a Human Being Struck by a Moving Vehicle

    How do you calculate the amount of pounds per square inch force on say a female human being approximately five feet tall at 185 pounds at rest being struck by a moving vehicle at motion by gravity with a curb weight of 2700 lbs going 4 mph.
  42. M

    Impact force on a falling object that spreads

    Hi, Homework Statement I'm doing some research into the hydraulic jump and was wanting some help in calculating the impact force. Hydraulic jump is a phenomenon to do with the turbulence of the water - it is the 'ring' around the stream of water when a tap is turned on Homework Equations The...
  43. M

    Impact Force of a falling object causing it to spread out

    Hi, I'm doing some research into the hydraulic jump and was wanting some help in calculating the impact force. The equation I have found to use is: F = m g h / s I have the mgh, and was wondering what to use as the slow down distance. If you didn't know what the hydraulic jump was, it is a...
  44. M

    Impact force calculation of a Full Suspension Mountain Bike

    Hello Folks! I want to find the maximum applicable force on a full suspension mountain bike and i will use this force on a FEA software structural analysis for a uni design project. This bike has a rear suspension with 400 lbs/in spring rate.Also rear wheel vertical displacement(travel amount)...
  45. B

    Water Jet Impact Force Calculator

    Hi, I've got this water circulation system. Diagram attached: http://postimg.org/image/wmf2hql6p/ In the upper container jets of water come out from the pipe due to the small holes I have drilled into the sides. I would like to know how I can work out the impact pressure on surfaces that may...
  46. C

    Is Impact Force Equal to G-Force in Newtons?

    Hi, I am dropping an object of mass m at different heights on another body. From the accelerometer I have I can get the g-force and then convert it into Newtons. What I am wondering, is the force converted into Newtons equal to the impact force the mass exerts on the body?
  47. J

    Maximum impact force that a cable can withstand

    Homework Statement " A 1100 kg lift is suspended by a series of 24 steel cables of mean diameter 20mm. The cables are attached to the lift top and are arranged so that torsional vibration is minimised.If the cable is manufactured from steel with an elastic modulii of 185GN/m2 and elastic...
  48. H

    Measuring impact force on rubber spacers

    I need to find the impact force that can be absorbed by these spacers as shown in the image. The spacers are radially distributed over the shell, and they are supposed to dampen any external impact loads to reduce the effective stress inside the inner shell. Since the FEA model is not showing...
  49. S

    How to work out the impact force of a colision

    Hi :) Here is a true story... I was in my car which weighs 820 Kgs, I for arguments sake weighs 80Kgs and the vehicle has an acceleration of 0-100 Kph in 15sec I was at a stop and went to go around a stationary vehicle in front of me.. I locked the wheel and attempted the pass but instead made...
  50. T

    Calculating Impact Force of a Schmidt Hammer

    Hi! I have apparently forgotten way too much college physics, and could really use some help here. I'm trying to calculate the impact force of an instrument (a Schmidt hammer--uses a spring-loaded piston) that produces an impulse against a surface. The instrument registers a rebound value (which...