# Impact Energy Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Nov 21, 2022

The impact energy calculator will help you determine the energy associated with impact loads. An impact load refers to the application of high force in a short time. Examples of such cases include a footballer kicking a ball, two objects colliding with each other, a bird strike, or a car crash. You can read more about forces in a car crash in car crash calculator.

Impact loads on an object are often catastrophic, as the material response is brittle due to very short interaction time. Structures are tested for resilience against these loads. A branch of science is dedicated to studying the dynamic response of materials under these loads, i.e., impact mechanics. The findings are useful for designing structures for defense as well as civil purposes.

This calculator and the accompanying article will teach you what impact load is and how to calculate impact energy.

When a large force is applied to an object for a short time, it results in an abrupt transfer of momentum and energy. Such energy transfer causes brittle material behavior and is known as impact loading. The resulting stress waves travel within the structure (refer to speed of sound in solids calculator). The velocity of the stress wave depends on the density and Young's modulus of the material.

The interaction time of the load is very short, and therefore, such loads are dynamic in nature. There are 4 different types of impact loads based on velocity:

Category

Velocity

Low-velocity impact

<10 m/s

Intermediate velocity impact

10-50 m/s

High-velocity impact

50-1000 m/s

Hypervelocity impact

>2.5 km/s

The low-velocity impact loads are usually a large mass impacting with objects such as tool drops or a football. The intermediate velocity impact loads involve debris from hurricanes or blasts, foreign objects hitting an aircraft, etc. The high-velocity impact is mainly observed in defense, i.e., bullets from firearms. The hypervelocity impact involves the projectile moving at very high velocities, such as asteroids and meteorites.

The energy associated with the impact load is a function of the mass and velocity of the impactor, along with the collision time and distance. Similarly, the impact force is the force exerted by the impactor on the object.

Impact tests
Impacts can be desirable, such as impact testing like Izod or Charpy impact tests, which are helpful in the determination of fracture toughness of materials. You can read about these tests in impact test calculator.

## Impact energy – Impact force calculation

Consider an impactor with mass, $m~\mathrm{[kg]}$ traveling at a velocity of $v~\mathrm{[m/s]}$, and collides with a stationary object. The kinetic energy of the impactor is the impact energy, $E$, i.e.,

$E = \frac{1}{2} m v^2$

The impact force, however, depends upon two more factors — the collision distance and collision time. Considering a collision distance of $d~\mathrm{[m]}$, the average impact force is:

$F = \frac{1}{2d} m v^2$

Similarly, if we know the collision time, the average impact force is:

$F = \frac{mv}{t},$

where $t = t_1 - t_0$ is the interaction or collision time.

The peak force is twice the respective average values.

## Using the impact energy calculator

This calculator has two modes based on the data available to you. You can either use collision distance or collision time to calculate impact energy and force.

Let's estimate the impact force on a golf ball impacting at 5 m/s with a collision distance of 0.5 m. To find the impact energy:

1. Select collision distance as calculation parameter.

2. Insert the mass of golf ball as $m = 45.9~\mathrm{g}$.

3. Fill in the velocity as $v = 5~\mathrm{m/s}$.

4. Enter the collision distance as $d = 0.5~\mathrm{m}$.

5. The average force is:

\scriptsize \qquad \begin{align*} F &= \frac{1}{2d} m v^2\\[1em] &= \frac{1}{2 \times 1} 45.9 \times 10^{-3} \times 5^2\\[1em] &= 1.148~\mathrm{N} \end{align*}
1. The impact energy calculator returns maximum force as 2.295 N.

## FAQ

### What are the type of impact loads?

There are four types of impact loads depending upon the impact velocity — low (LVI), intermediate, high (HVI), and hypervelocity impact. The velocity range for the categories is less than 10, 10-50, 50-1000, and greater than 2500 m/s, respectively.

### What is impact energy?

When a moving body and a stationary body, or two moving bodies, collide, they lose and gain momentum. The force and energy associated with this interaction are known as impact force and impact energy, respectively. In the case of one moving body, the impact energy is equal to the kinetic energy of the moving body.

### How do I calculate impact energy?

To calculate impact energy:

1. Find the velocity of the moving object.
2. Determine the square of velocity of the moving object.
3. Multiply the resultant with the mass of the object.
4. Divide the product by 2 to obtain the impact energy.

### What is the impact energy associated with a football kick hit at 10 m/s?

The impact energy of a soccer ball moving at a velocity of 10 m/s is 22.5 J. Considering a soccer ball is about 450 g, the impact energy is the kinetic energy of the ball, i.e., E = 0.5 × 10² × 0.45 = 22.5 J.

Rahul Dhari
Calculate impact force using
collision distance
Conditions
Mass (m)
lb
Velocity (v)
ft/s
Collision distance (d)
ft
Impact force & energy
Average force (Fₐ)
lbf
Maximum force (Fₘₐₓ)
lbf
Energy (E)
ft-lbs
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