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2. A car is a compound machine 2 It is made up of many simple machines

3. One of the most important parts of a car is its engine 3 Vocabulary: engine A compound machine

4. In most cars the engine gets its energy from gasoline 4 Gasoline is a fuel

5. 5 Engines that use gasoline as their fuel are called gasoline engines A gasoline engine has up to eight tubes called cylinders

6. 6 The engine also has a carburetor where gasoline is mixed with air The carburetor sends this mixture to the cylinders

7. Some gasoline engines do not have carburetors 7 Instead a fuel-injection system squirts fuel into the cylinders

8. Each cylinder has its own spark plug 8 When the mixture of gasoline and air reaches the tops of the cylinders the spark plugs start little fires

9. The gases from the fires push on pistons inside the cylinders 9 The pistons move up and down

10. The up-and-down motion of the pistons moves another part of the engine 10 called a crankshaft

11. 11 and for the car to move The motion of the crankshaft gives the energy the car needs for the wheels to turn

12. Gasoline engines are not only in cars. 12 They can also be used in lawn mowers, small boats, trucks, and propeller airplanes

13. Most large airplanes today are powered by jet engines 13 Jet engines are compound machines

14. Air goes into the jet engine 14 A compressor squeezes the air, which is then mixed with fuel

15. The fuel mixture burns and produces hot gases 15 The gases turn a turbine wheel that runs the compressor

16. 16 Then the gases rush out of the engine toward the tail of the plane

17. Jet engines work because of one of the laws of motion 17 Remember that for every action there is an equal and opposite reaction

18. The reaction is the motion of the plane in the opposite direction 18 The action is gases rushing out of the engine

19. The gases do not need any matter to push against 19 Even without air, a jet plane would fly

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