How to Calculate Bomb Speed

Bomb use must be planned to eliminate as much possibility of error as possible.

The act of dropping a bomb requires extensive planning and preparation to ensure the bomb performs as expected without any more casualties than necessary. If a bomb is targeted at a military base for example, it should not fall and detonate on a children's school. Precise calculations are made regarding the bomb's weight, the speed of the plane making the bomb run and the effect of current weather conditions to make an air strike as surgical as possible in its precision. Calculating a bomb's speed as it drops is a matter of some basic physics.

Things You'll Need

• Scale
• Tape measure
• Calculator
• Drag coefficient table

Instructions

1. Determine the weight of the bomb. If this is for a math question, the weight should be given. In practical determination, you would need to weigh the bomb on a scale.

2. Measure the diameter of the front cross-section of the bomb that would face down in a freefall. Measure across the cross-section with a tape measure. Determine the area by dividing 3.1416 (pi) by four times the diameter squared.

3. Calculate the drag coefficient, which is the amount of force exerted on the bomb as it moves through space in freefall. The coefficient also affects the plane that is dropping the bomb. Since atmospheric conditions are never known precisely beforehand, the coefficient is always an estimate based on theoretical data. There is normally a drag coefficient table that will provide this number based on the current weather conditions in the area in which the bomb is being dropped.

4. Write down the altitude at which the bomb is dropped. The overall altitude affects the bomb's speed because air pressure is lower at higher altitudes, meaning the bomb will accelerate more quickly than at lower altitudes where resistance is more of a factor.

5. Enter the bomb's weight in pounds, cross-section area in square feet, drag coefficient number and bomb altitude in feet into a terminal velocity calculator. NASA provides one on its website that can be used to calculate terminal velocity, which ends up being the bomb's top speed in freefall where acceleration stops.

References

• NASA: The Drag Coefficient
• Engineering Toolbox: Drag Coefficient
• The Physics Zone: Terminal Velocity

Resources

• NASA: Terminal Velocity Calculator