CH 12 Worksheet - Work and Simple Machines

Middle School
Physical Science WS
Ch 12 - Work and Machines

1. What is the definition of work?  when you exert a force in a certain direction and the object moves in that direction
2. What is the equation for work?  w = force x distance
3. What unit is used to measure work? joules
4. Does it take more work to lift a book onto a table or to hold the book over your head?  it takes more work to lift the book to the table  Why?   Because when you hold the book over your head the book is not moving and therefore no work is being done at all.
5. Calculate the amount of work done in this situation:
1. A girl exerts 100 N to lift a box 2 meters onto a shelf.  How much work did she do? 200joules
2. A girl slides the same box up a 5 meter ramp to the same shelf using 40 N of force.  What was the amount of work done this time?  200joules
6. Draw a picture that illustrates one of the situations from the word problem in number 5. Label the force and distance.  (answers may vary)
7. What is Power? Power is the amount of work that can be done per second
8. What is the equation for Power?  power = work ÷ time
9. What is the unit used to measure Power? Watt
10. Solve this problem:  A boy can push a wheelbarrow across the yard (10 meters) using 10 Newtons of force.  It takes him 50 seconds to do it.  How much power was used in this process?  (10 x 10) ÷  50 = 2 Watts
11. A simple machine can make work easier in 1 of three ways.  List the three ways:
1. change the direction of the force
2. change the amount of work required
3. change the amount of distance 
12. List 6 types of simple machines and tell one example of each
1. incline plane = ramp
2. wedge = axe, knife
3. screw = lid of a jar, screw
4. lever = scissors, paint can opened, car jack
5. Wheel and Axle = screw driver
6. Pulley = Pulley, crane, belay system (rock climbing)
13.  Name 2 types of machines that can be used to change the direction of the force?  Pulley, lever
14. Name one machine that can be used to reduce the amount of force needed to lift an object? Pulley or lever
15. In the following picture of a lever, would the amount of force pushing UP on the load be greater or lesser than the amount of force at the end with the arrow. 
    
    It would be greater because distance from the fulcrum to the load is smaller.
16. How do you determine the mechanical advantage of a simple machine?  Write the equation here:  
1. M.A. = weight  ÷  apparent weight     or       
2. M.A.  =  weight ÷ amount of force needed to move it
17. When we use a simple machine to move an object, it can reduce the apparent weight of the object.  In the following chart some of the information is missing.  Use what you know about mechanical advantage, weight and apparent weight to fill in the chart.

Original Weight      M.A.     Apparent Weight
10 N                         1                      10N
30 N                         3                       10N
50N                          2                       25N
100N                         4                       25N

18.  In the human body   
  
        Would you say that your teeth are more like a wedge or more like a pulley?
        Would you say that your arm acts more like a lever or more like a screw?