Form 3 Experiments
Theme 2: Balancing Forces
Aim: To investigate Moments of PARALLEL FORCES
OBJECTIVE: To become better acquainted with the principles of
moments and with the conditions required for equilibrium.
Focus Questions
1.
Why do we place handles on doors on the opposite side of the
hinges?
2.
Why do we use a teaspoon to open a tin of coffee?
3.
Is it better to loosen a tyre bolt with a long spanner or a
short one?
4.
What are the conditions necessary for equilibrium?
5.
On a seesaw where must the heavier person sit (close to the
pivot or away) in order to reach equilibrium with another
person of smaller weight.
6.
If we say that an object is under the influence of forces which
are in equilibrium what do we mean?
7.
When an object is in equilibrium how are the anticlockwise
moments related to the clockwise moments?
Safety Notes:
In this experiment, we will use a meter stick balanced in a horizontal
position so that the length of the moment arms may be calculated using
positions obtained directly from the meter stick. The forces will be due
to gravity and hence will be vertical. There is likely to be some slight
differences between the calculated values and the experimental values
due to friction, discrepancies in the weights used, and difficulty in
reading the meter stick with great accuracy.
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Date: ____________
Theme 2: Balancing Forces
Aim: Experiment to investigate Moments of Parallel Forces
Apparatus: Ruler with regular markings, Metal masses, stand and
clamp, mass balance, nail, paper clips.
Sources of error and precautions 1.
2.
Method
1. Suspend the metre ruler from its centre from the nail attached to the
stand and clamp. The nail will act as a pivot.
2. Use a paper clip to balance the wooden strip so that it is as horizontal
as possible. Fix the paper clip with a little Sellotape.
3. Place some weights on the on the right hand side of the ruler near
the pivot. What do you notice? Why? Calculate the moment of this force?
Now move the masses away from the pivot? What do you notice? Did the
moment of the force increase? Why?
4. Now move the weights on the right hand side of the ruler to the left
hand side. What do you notice? Why? Calculate the moment of this force?
Predict what masses and at what distance must they be place on the right
hand side to balance this ruler?
5. Now place the second set of masses on the right hand side to test
your prediction. Move them on the ruler until it is horizontal once
again. Record the number of masses and hence the force in newtons
and their distances from the pivot in table 1.
6. Repeat step 5 using different masses and distances from the pivot
and record them in the table1.
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7. Now move the pivot to the left, at the 20 cm mark. Where is the weight
of the ruler considered to be located? Why? Place some masses on the left
hand side and move them until the beam is horizontal once again.
8. Record the number of masses and hence the force in newtons and
their distances from the pivot in table 2. Record also the distance of
the centre of gravity of the ruler and the pivot?
9. Repeat step 8 three times by varying the masses and distances on
the left hand side. By using a mass balance record the mass of the
meter beam.
Results:
1. Moment of clockwise force =
2. Moment of anticlockwise force =
Table 1
Clockwise Moments
Force N
Distance
from pivot
Moment
of force
Anti Clockwise Moments
Force N
Distance
from pivot
Moment of
force
1
2
3
4
5
Do you spot any pattern in the result.
Table 2
Clockwise Moments
Anti Clockwise Moments
Force N
Distance
from pivot
Moment
of force
Force N
(weight beam)
Distance
from
pivot
Moment
of force
1
2
3
Mass of meter beam = ___________________________-
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Conclusion /Evaluation:
1. Make a diagram of your apparatus setup.
2. What did you notice when masses were added on the left hand side of
the beam? Why? What happened to the moment of the force when the
distance from the pivot was increased? Why?
3. Did you spot any pattern in the results of table 1? If yes what was the
pattern? If not how could you improve this investigation to obtain
better results?
4. From information gathered in table 2 calculate the mass of the meter
stick.
5. How close are the three values for the weight of ruler obtained in
table 2 to one another? Should they have been the same?
6. Find the average mass of the beam from your table and compare it to
the real weight of the wooden beam. Is it close? If not what do you
thing contributed to this difference?
7. Discuss the major sources of error that would account for your
discrepancies.
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