Magnets are able to place a force on certain materials. This force is called a magnetic force. The force a magnet exerts is a little different from the forces you may normally think about. You exert a force on a book when you lift it. You also exert a force on the pedals of your bicycle. In both those cases, those forces cause a change. The change you see in both these cases is called motion. Magnets, too, can produce change. They can produce motion just like you do. Unlike you, magnets do not have to touch something to exert a force. A magnetic force is exerted over a distance. Thats right, a magnet can push or pull certain items without ever touching them. Thats how the maglev train works. Do you know another type of force that does not require objects to touch? These forces are known as non-contact forces. Another type of non-contact force you may be familiar with is gravity. Gravity too can cause changes in motion. Gravity holds our moon in orbit without touching it.
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QUESTION: What are a few examples of non-contact force?

Rough surfaces create more friction than smooth surfaces. Thats why cars have tires. Its also why we use rubber mats in areas that might get wet. In your bathtub, you may even use No-Slip tape. No-slip is another way of saying the items has a lot of friction. In Figure 1.9, the blades of the skates are very smooth. Thats why you cant slide across ice with shoes. The soles of your shoes are much rougher than skates. The rougher surface of shoes causes more friction and slows you down. Heavier objects also have more friction. A heavy object presses down with more force. The surfaces are held together more tightly. This makes the surfaces harder to slide past each other. Did you ever try to push something heavy across the floor? Heavy objects are much harder to push than light objects.
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QUESTION: In order to slide across ice more easily, would you want something on your feet that had a smooth surface or a rough surface?

Relying on an animal to come by is risky. A flower may have to wait a long time for the right animals to come by. What if one never passes close enough to the flower? Hoping the wind will blow is also risky for a plant. What if the wind does not blow? What if the blowing pollen does not land on another flower? The wind could even blow the pollen over the ocean where it is wasted. Giving free nectar is costly. It is not a good use of the plants energy. A plant uses a lot of energy to produce nectar. Some animals may just drink the nectar. They may not carry off any pollen in return. To improve their chances, plants evolved special traits. For example, they developed ways to hide their nectar. Only certain animals were able to get at the plants hidden nectar. These specific animals might be more likely to visit only flowers of the same species. This was also a benefit for some animals. Animals also evolved special traits to get to the nectar.
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QUESTION: Why is giving free nectar costly?

Crusaders, Mamelukes, and Turks: The Crusaders established a feudal Christian state with Godfrey at its head. They built many impressive churches during the term of the first Latin Kingdom of Jerusalem, but in 1187 they were driven out by Muslim forces under the great warrior Saladin. During the Sixth Crusade (1228 1229), the Holy Roman Emperor Frederick II managed to secure Jerusalem for the Christians by negotiation. The Christians, however, could not hold the city. After they lost Jerusalem, a Mongol invasion swept through, and in 1244 the Mameluke dynasty of Egypt took control, ruling Jerusalem for the next 250 years. The city struggled to rebuild from Crusader wars and invasions. Much of the best Islamic architecture in the city was constructed in the Mameluke era, but the past thousand years had taken their toll: Jerusalem was unable to regain the prosperity it had enjoyed in earlier times. In the early 16th century, the Ottoman Turkish Empire was advancing through the Middle East. Jerusalem fell to the Ottomans in 1517, remaining under their control for 400 years. Suleiman the Magnificent rebuilt the walls and gates in the form they retain to this day. Fountains, inns, religious schools, and barracks were constructed. But when Suleiman died, his empire, including Jerusalem, began a long period of decline. The Holy City remained a backwater until the 19th century, when renewed interest among Christian pilgrims made it the destination of thousands of travelers each year.
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QUESTION:
What happened during the Sixth Crusade with the Christians?