8-forces+and+machines

forces and machines examples: Which of these objects has a screw? b-ramp (for disabled people in wheel chair) c-saw d-ladder
 * a-bottle cap**

This is a non-contact force: a-frictional force c-normal force d-spring force
 * b-gravitational force**

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7.What type of force requires two pieces? =====

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9.What force is what keeps us on Earth? =====

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10.What two concepts takes into account the acceleration? =====

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11.How many objects have to be in contact for friction to occur? =====

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13. Why does a ball stop on the floor without somebody´s intervention? =====

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 *  b) ****because of friction **=====

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14. What happens if we throw a ball downward out of a window? =====

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17. What other material besides solids can cause friction? =====

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19. The inclined plane consists of: =====

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20. When you screw a hinge into a door: =====