Force is a vector. What then is a vector? Think about how you would give directions to a friend. You would not say, just walk half a mile. The person may walk a half mile in the wrong direction! More information is needed. You may say, follow this particular road for a half mile. You may say, look for the green house on Sumter St. In both examples, you provided a direction. You also gave the distance. In other words, you provided a vector. You did not just give a distance. Both pieces of information are needed to find a location. This is just like describing forces. To explain forces, both size and direction are needed. Notice the girl in Figure 1.1. She is pushing the swing away from herself. Thats the direction of the force. She can give the swing a strong push or a weak push.
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QUESTION: When you say, "Follow this particular road for a half mile," what kind of information are you providing in addition to distance?

Zinni feared that Bin Laden would in the future locate himself in cities, where U.S. missiles could kill thousands of Afghans. He worried also lest Pakistani authorities not get adequate warning, think the missiles came from India, RESPONSES TO AL QAEDA'S INITIAL ASSAULTS 135 and do something that everyone would later regret. Discussing potential repercussions in the region of his military responsibility, Zinni said, "It was easy to take the shot from Washington and walk away from it. We had to live there." Zinni's distinct preference would have been to build up counterterrorism capabilities in neighboring countries such as Uzbekistan. But he told us that he could not drum up much interest in or money for such a purpose from Washington, partly, he thought, because these countries had dictatorial governments. After the decision-in which fear of collateral damage was an important factor- not to use cruise missiles against Kandahar in December 1998, Shelton and officers in the Pentagon developed plans for using an AC-130 gunship instead of cruise missile strikes. Designed specifically for the special forces, the version of the AC-130 known as "Spooky"can fly in fast or from high altitude, undetected by radar; guided to its zone by extraordinarily complex electronics, it is capable of rapidly firing precision-guided 25, 40, and 105 mm projectiles. Because this system could target more precisely than a salvo of cruise missiles, it had a much lower risk of causing collateral damage. After giving Clarke a briefing and being encouraged to proceed, Shelton formally directed Zinni and General Peter Schoomaker, who headed the Special Operations Command, to develop plans for an AC-130 mission against Bin Laden's headquarters and infrastructure in Afghanistan. The Joint Staff prepared a decision paper for deployment of the Special Operations aircraft. Though Berger and Clarke continued to indicate interest in this option, the AC-130s were never deployed. Clarke wrote at the time that Zinni opposed their use, and John Maher, the Joint Staff 's deputy director of operations, agreed that this was Zinni's position. Zinni himself does not recall blocking the option. He told us that he understood the Special Operations Command had never thought the intelligence good enough to justify actually moving AC-130s into position. Schoomaker says, on the contrary, that he thought the AC-130 option feasible. The most likely explanation for the two generals' differing recollections is that both of them thought serious preparation for any such operations would require a long-term redeployment of Special Operations forces to the Middle East or South Asia. The AC-130s would need bases because the aircraft's unrefueled range was only a little over 2,000 miles.
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QUESTION: Who lobbied for the decision paper written by the Joint Staff?

Surely, you have noticed the tall poles along the roadside. Do you know what is on top of those poles? Thats right, wires that carry electric current. These wires carry electric current to your home. But what is electric current? Electric current is actually the flow of electrons. You may recall, an electron is the outer-most particle in an atom. They have a negative charge. Electricity is the continuous flow of these particles. Electrons are able to move through wires. Their speed can even be measured. The SI unit for electric current (or speed) is the ampere (A). Ampere is often shortened to amp. Electric current may flow in just one direction, or it may keep reversing direction. Direct current (DC) flows in only one direction. Direct current is what is used in devices like flashlights. Alternating current (AC) flows in two directions. This is the type of current that flows into your home through wires.
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QUESTION: What is an Ampere?

You know that friction also causes heat. Think about when you rub your hands together. It is friction that makes them warm. But why does this happen? Friction causes the molecules on rubbing surfaces to move faster. Faster moving particles have more heat energy. Heat from friction can be useful. Can you think of other places where you might find friction? Friction also lets you light a match. Heat from friction can also cause problems. It can cause a car to overheat. To reduce friction, oil is added to the engine. Oil coats the surfaces of moving parts. This coating of oil makes them slippery. When things are slippery there is less friction. Have you ever seen a sign that says, slippery when wet? This too has to do with friction. Water, like oil, can reduce friction. The wet surface may allow your shoes to slide more easily.
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QUESTION:
Why do your hands become warmer when you rub them together?