Aim
To find out how a number of pulleys affect the effort needed to lift a load of 1 Newton (100g).
Hypothesis
I predict that as the number of pulleys we use increases, the effort needed to lift the pulley will decrease.
Fair test
There are many factors that could affect the results in this experiment all of which will have to be kept under control, if they were not kept under control then the results would not be fair. We will keep the test fair by keeping the load the same (1 Newton), by keeping the size of the pulley the same, by keeping the material the pulley is made from the same and the thickness of the rope the same.
Method
1. Attach the pulley with a loop of string to a clamp stand.
2. Place a piece of string over the pulley.
3. Put small loops on either end of the string.
4. Attach load to one side of the string and attach the effort to the other. The effort force could be measured with a Newton metre so we are going to use a counter balance masses instead.
5. Record the force needed to lift the load by 0.1m.
Repeat the above experiment with 2-pulley system and 3-pulley system.
Results
Pulley number
Load force (N)
Actual mass of counter balance
Actual effort (N)
Theoretical effort (N)
Friction in system (N)
1
1
100g
1.0712
1
0.0712
2
1
50g
0.642
0.5
0.142
3
1
10g
0.5867
0.33
0.2567
Calculations
Pulley number
Friction in pulley system (N) (actual effort-theoretical effort)
Mechanical advantage
= Load (1N) /effort
Energy output= Load (1N)
Distance moved (m)
Energy input=actual effort using counterbalance method
Distance effort rope pulled through
Efficiency =(energy output /energy input) 100
1
0.0712
0.933
0.1
0.107
93.45
2
0.142
1.1557
0.1
0.128
78.125
3
0.2567
1.704
0.1
0.176
56.81
Pulley number
Theoretical effort force to lift a 100g (Newton) load (N)
Distance I pulled rope through (m) to lift a load
10cm
Theoretical energy input if no friction (= theoretical effort)
Actual mass of counter balance g (mass and coins)
Actual effort to lift pulley (Newton’s) using counterbalance method
1
1N
0.1
0.1
100g +7.12
1.0712
2
0.5N
0.2
0.1
50g +14.24
0.642
3
0.33N
0.3
0.1
10g + 48.57
0.5867
Conclusion
As the results table’s shows, the actual effort to lift the pulley (Newton’s) decreases as the pulley number increases. This is because the more pulleys that are involved make it easier to lift the load. The actual effort is not identical to that of the theoretical effort although they are similar. Whilst conducting this experiment it is important that the friction between the pulley and the rope is taken into account. If this is not dealt with then the results will not be accurate. The more pulleys that are used means more friction is occurring. Friction occurs between the axle and the wheel as the wheel turns and as the rope passes over the pulley.
Evaluation
After competing this experiment it is possible to overlook some of the potential problems that may occur. The first problem was that the pulley itself was not very stable, this could also be due to a poor clamp, and often collapsed. Another problem that we occurred was that as the ropes passed each other they produced a lot of friction. This friction also occurred between the axel and the wheel, which made the experiment slightly more difficult than it, should have been.
