8th- Chapter 12 Study Guide Answers

1. What must happen for work to be done on an object? An object must have motion and move in a direction the same as the force acting on it.

2. Give an example of work. Ex. Shoveling dirt, pushing a child in a swing, picking up your backpack

3. If you exert a force of 30N to push a desk 8 meters, how much work did you do on the desk? 30 x 8 = 240 J

4. What are the units of work? Joules (J)

5. What do machines do? Machines make work easier!!

6. Pulling down on a rope to hoist a sail on a sailboat is an example of a machine doing what? 1) decreases the amount of input force needed to lift the object. 2) the pulley can change the direction of your input foce.

7. The mechanical advantage of a machine is the number of times a machine increases __________. Force

8. How would input work and output work compare if there was no friction? They would equal each other

9. An ideal machine would have what efficiency? 100%

10. Give an example of an inclined plane? A ramp in a parking garage.

11. What is a compound machine? Give an example. Compound machine- a machine that utilizes two or more simple machines. Example: apple peeler

12. The simple machines that is an inclined plane wrapped around a cylinder is the ___________. Screw

13. What is a fulcrum? The fixed point that a lever pivots around.

14. In order to do work on an object, the force you exert must be ____________. In same direction that the object moves.

15. Work equals force times ______. Force X Distance

16. When you raise or lower a flag on a flagpole, you are using which simple machine? Pulley

17. What is the MA of a machine that changes only the direction of force?

18. If tight scissors have an efficiency of 50% half of your work is wasted due to ____________. Friction

19. The power of a light bulb that converts electrical energy at a rate of 100 Joules per second is? 100 Watts Because 1 Joule/second = 1 Watt

20. Power is measured in what units? Watts

21. A newton-meter is also known as the ____________. Joule

22. What is the input force? The force that you apply to a machine.

23. What are the three ways a machine makes work easier? 1) increases force 2) distance 3) direction

24. All machines have an efficiency of what? Less than 100%

25. The ideal MA would equal the actual MA if there were no __________. Friction

26. What is the efficiency of a machine if the output work is 14,000J and the input work is 18,000 J. 14,000 / 18,000 = .77 x 100% = 78%

27. A jar lid is an example of what simple machine? Screw

28. A screwdriver is an example of what simple machine? Page. 428 says that a screwdriver is a wheel and axle

29. When you bite into an apple, your front teeth are acting as what simple machine? Wedge

30. Power is equal to ________ divided by time. Work