ACTIVITY: Force, Work, and Machines
EQ: How do simple machines affect work?
BACKGROUND INFORMATION: (leave 3 lines)
RESULTS:
PART 1 Building a simple machine
Table 1: Input and Output Force
Number of Strings
1
2
3
4
5
6
Input Force (N)
10.1
5.1
3.4
2.5
2.1
1.7
Output Force (N)
10.1
10.1
10.1
10.1
10.1
10.1
THINKING ABOUT WHAT YOU OBSERVED:
1. As you increase the number of supporting strings, what happens to the force needed to lift the bottom
block? (2 lines)
2. The number of strings ___________ the force needed to pull the yellow string in order to lift the bottom
block ___________ the weight of the bottom block.
3. What does the term mechanical advantage mean for a simple machine? (5 lines)
4. Calculate the MA for each supporting string in the table below.
Table 2: Number of strings vs. mechanical advantage
Number of Strings
Mechanical Advantage
1
2
3
4
5
6
(Use data from table 1 )
PART 2: The input and output distance
Table 3 Force and distance data
Mechanical
Output Force (N)
Advantage
1
10.1
2
3
4
5
6
Output Distance
(m)
0.20
Input Force (N)
Input Distance (m)
10.1
5.1
3.4
2.5
2.1
1.7
.20
.40
.60
.80
1.0
1.2
THINKING ABOUT WHAT YOU OBSERVED:
1. As the MA increases, what happens to the length of the string you have to pull to raise the block? (2
lines)
2. What is the specific meaning of work in science? (2 lines)
3. What do you trade for using less input force to move the block? (2 lines)
4. Calculate the output work done on the block. (1 line)
W=FOdO (See table 3)
5. Calculate the input work. Table 4: Calculations of work put into a machine
Input Force (N)
Input Distance (m)
Work Done (J)
10.1
.20
5.1
.40
3.4
.60
2.5
.80
2.1
1.0
1.7
1.2
6. For each MA, how do input and output work compare. (copy answers from question 4 and table 4)
Table 5: Comparison of input and output work
Mechanical Advantage
Input Work (J)
Output Work (J)
1
2
3
4
5
6
Copy input work from table 4 above.
Output work – multiple fo times do from table 3
SUMMARY: (Compare WI to WO) One short sentence.
7. Is output work ever greater than input work? Why? (2 lines)
TEACHER NOTES
MA of pulleys
The number of supporting strings is about equal to the mechanical advantage.
If MA<1, output force is less than input force.
If MA>1, the output force is greater than the input force.
As the input distance increases, the amount of input force needed to lift the block decreases.