# Momentum Misconceptions

As is usually the case, TV and movies are constantly reinforcing "bad" physics and making misconceptions.  A very common misconception is that if a person gets hit by a bullet, they will immediately fly backwards and break any window they were standing in front of.

In this animation, if the bullet had a realistic mass (0.04Kg) and a realistic velocity (300m/s) then the only way the person would fly backwards as shown is if the person had a mass of less than a kilogram.  Since people typically have masses ranging from 45Kg to 120Kg, we already start getting the idea that the movies don't follow the law of conservation of momentum.

If the impact of a bullet and a person were shown realistically, it would be much less dramatic.  In fact, if we created the ideal situation of a person on ice skates (to reduce friction) we would still barely notice the movement of the person as seen in the simulation below which uses a realistic bullet (0.04Kg at 300m/s) and a realistic person (65Kg) and treats the collision as completely inelastic (the bullet sticks).  Try the calculation for yourself, you'll find the person only goes 0.18m/s.

The other way of thinking about this is to say, if the bullet has the ability to throw a person through a window, what would the recoil of the gun have done to the shooter?  If the gun doesn't throw the shooter off his feet, the bullet can't throw the target of his feet.