I like how Lee Child writes, and I usually find in his books nothing worse than a couple of typos. But in the book I am currently reading, Personal, he made a bad mistake. So bad that I cannot remain quiet about it! In fact, I have to write about it at once, even if I have only read less than a quarter of the novel.
A question of force, obviously, which is the product of mass times velocity square, and that squared [his Italics] part puts a premium on speed, not weight.Now, forces are measured in Newtons (N=kg*m/s2). The formula ½ M V2 refers to the kinetic energy of a moving body and is measured in Joules (J=kg*m2/s2, or J=N*m). They are different things.
He then goes on with the following explanation:
Bulking up by twenty pounds at the gym is good, because it throws an extra twenty pounds in the mix, but moving your foot 20 per cent faster is better. It does you 400 per cent of a favour. Because it gets squared. Which means multiplied by himself. Money for nothing.How painful! I don't remember how heavy Jack Reacher is, but twenty pounds will be about 10% of his weight. The kinetic energy of a body 10% heavier is 10% higher. If, on the other hand, the body moves 20% faster, its kinetic energy increases by 44% (because the energy at the higher speed is 1.22 = 1.44 times the original energy). Did Child obtain his 400% by dividing 44% by 10%? I don't know. But one thing is clear: the whole paragraph is muddled. And all those full stops don't make it clearer. And why should your weight be relevant when you kick a door with your foot?
The door and the door jamb have a certain elasticity, and you have to apply enough force to them in order to exceed the limit of what they can take. If you remain well below the limit, the door flexes by an amount proportional to the force you apply (Hooke's law) and it returns to its original condition when you stop pushing. Admittedly, a door is not as flexible as, say, a stick. But the principle is the same: if you were strong enough, you wouldn't need to kick a door in order to knock it down. You could just push with increasing pressure until it breaks.
When you kick a door, your foot almost completely comes to a stop, thereby losing its kinetic energy. The sole of your shoe and your foot and leg compress (similarly to when you squeeze a rubber ball) and the door and door jamb flex (like when you bend a stick). But if you hit with more and more energy (and assuming that you don't break your foot), the elasticity of the door cannot absorb it, and an increasing portion of that energy goes into deforming and, ultimately, breaking the door.
If you divide the kinetic energy of your foot by how much the door can bend, you have a rough estimate of the force that you apply to the door when you kick it. So, all in all, as the flexibility of the door is what it is and the mass of your foot also doesn't change, it is true that the only thing you have an influence on when you want to kick down a door is the speed of your kick. But Child's explanation is still muddled because he confuses energy and force and states that the weight of the whole body is relevant.
Child also made an impossible assertion on page 93:
the table was loaded with a long line of twelve laptop computers. All of them were open to the exact same angle, and all the screens were showing the exact same things, which were animated Police nationale screensavers, moving slowly but purposefully around the screens, all in lock stepWow! how do you synchronise the screen savers of twelve computers and keep them in sync? Assuming that the computers would sync their time via the network (which is a standard practice), the moving pattern would have to start at given times, rather than just keep going. And why would anybody want to do it anyway (except for impressing Reacher, that is)? What a concept...
For your reference, here are the links to all past “Authors’ Mistakes” articles:
Lee Child: Die Trying
Colin Forbes: Double Jeopardy
Akiva Goldsman: Lost in Space
Vince Flynn: Extreme Measures
Máire Messenger Davies & Nick Mosdell: Practical Research Methods for Media and Cultural Studies
Michael Crichton & Richard Preston: Micro
Lee Child: The Visitor
Graham Tattersall: Geekspeak
Graham Tattersall: Geekspeak (addendum)
Donna Leon: A Noble Radiance
007 Tomorrow Never Dies
Vince Flynn: American Assassin
Brian Green: The Fabric of the Cosmos
John Stack: Master of Rome
Dean Crawford: Apocalypse
Daniel Silva: The Fallen Angel
Tom Clancy: Locked On
Peter David: After Earth
Douglas Preston: Impact
Brian Christian: The Most Human Human
Donna Leon: Fatal Remedies
Sidney Sheldon: Tell Me Your Dreams
David Baldacci: Zero Day
Sidney Sheldon: The Doomsday Conspiracy
Christopher L. Bennett: Make Hub, Not War
CSI Miami #2 (Robert Hornak)
Jack Greene & Alessandro Massignani
P.Warren & M.Streeter