Physics Lab Report: Parallel Force
Aim: To test the principle of moments.
Apparatus: Metre rule with holes drilled at the 25cm, 50cm and 75cm mark, 50g masses 50mm long bolt with a diameter of approximately 5mm, retort stand, boss head and clamp, 0-10 N spring balance, electronic pan balance ,wire or string for suspending masses from the metre rule, two bulldog clips. Part A: Balancing a constant moment.
1. The experiment is set up by first placing the bolt through the rule, then the bolt is clamped with the boss-head. The rule must be ensured that it is balances horizontally before adding any weights. 2. The height of the pivot is adjusted so that when the rule is balanced the weights are a few centimeters above the bench top. 3. A 100g mass is hung between the 50cm mark and 100cm mark in a position so that the metre rule is balanced in the horizontal position. 4. The scale on the metre rule is used to measure the distance from the pivot point to the point where the second 100g mass is hung and record this value in the table 2 as shown below, in the column labeled. Distance to weight (cm). 5. Successive 50g masses is added and steps 2 and 3 are repeated for all mass values shown in the first column of Table 2.
Fixed Mass Data
Mas in grams (g)
Mass in kilograms (kg)
Distance from pivot (cm)
Distance from pivot (m)
Weight in newtons (N)
a c moment about pivot (Nm)
Mass used (g)
| Mass used (kg)
| Weight used(N)
| Distance to weight (cm)
| Distance to weight (m)
| Weight × Distance (Nm)
1. The range of the values obtained from the last column in table 2 is between 0.435Nm to 0.447Nm. The average value is 0.449Nm. 2. The average value obtained in the last column of table 2 is 0.439Nm. The difference between the clockwise moment obtained from the experiment carried out and the actual value is 0.002Nm. The percentage difference is 0.45%. 3. Clockwise torque is equals to anticlockwise torque.
4. It is because the pivot point is on the center of the mass of the rule. The mass is cancelled off as the lever distance is 0. 5. The length of the lever arm for the clockwise moment has to be increased as more weights at the fixed distance to the left of the pivot increases. This is because when more weights are added, the anticlockwise moment increases. To achieve equilibrium, anticlockwise moment must equals to clockwise moment. So at the clockwise moment where the mass is constant, the length must be increased so that the clockwise torque produced can balance the anticlockwise torque.
Part B: Balancing a variable moment
1. The equipment is set up as in Part A with a 100g mass at the 40cm mark on the rule. This will be at the fixed distance of 10cm from the pivot fir this part of the experiment. See the diagram below.
2. A 100g mass is positioned at the 40 cm mark and the rule is balanced by hanging a 100g mass on the other side of the pivot. The distance is recorded to the pivot of the second mass in table 3. 3. A further 50g mass is added to the first one at the 40cm mark and balance the rule by moving the 100g constant mass. Record the new balance position. 4. Steps 2 and 3 are repeated for each of the mass values shown in the first column of table 4. Values for constant moment
Mass of movable constant weight (g)
Weight of movable constant (N)
Distance from pivot of variable mass (cm)
Distance from pivot of variable mass (m)
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