# "Does the pulling force increase as the weight of the box increases and, if so, is the pulling force directly proportional to the weight of the box"

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Introduction

DRAGGING THE BOX INVESTIGATION "Does the pulling force increase as the weight of the box increases and, if so, is the pulling force directly proportional to the weight of the box" The design Prediction based on Scientific Knowledge When I apply the brakes on my bicycle a larger force from my hand produced a larger force on the brake blocks. This produces a larger frictional force on the wheel and I decelerate more quickly. The weight of the box is the force pushing down and so I predict that a larger weight will produce a larger frictional force. When pulling the block at constant speed the pulling force equals the force of friction and so I predict that a larger weight of box will produce a larger friction and need a larger pulling force. Proportionality means that if the weight of the box is doubled, the pulling force needed is doubles. I do not have any knowledge that would enable me to predict this. ...read more.

Middle

Diagram of the apparatus See separate sheet. The basic idea of the method Start with a weight on the wooden block and then start to pull the spring balance so it will then start to slip or you could just give it a gentle push to release it and then you take the reading straight away. The range of values for the weight of the box and how I decided on this range I did a preliminary experiment, I put 30N on the wooden block but I couldn't measure the pulling force with a 10N metre so I decided the range will go from 5N to 25N, going up in 5N Newton each time. The measurements to be taken 0N 0.7 0.6 0.7 0.6 0.7 0.7 5N 2.2 2.2 2.5 2.5 2.0 2.2 10N 3.3 3.5 3.6 3.6 3.7 3.6 15N 5.1 5.0 5.3 5.2 5.4 5.2 20N 6.8 6.8 6.8 6.9 6.7 6.8 25N 8.4 8.6 8.4 8.5 8.4 8.3 Observations Results table and calculation of averages (table from excel or a hand drawn one) ...read more.

Conclusion

The conclusions do agree with my original predictions because the graph I predicted is a straight line, the graph is a straight line therefore it suppors my predictions. Evaluation In carrying out the experiment I found it difficult to get the reading because it kept on wobbling. I found that the boards weren't long enough. If you pulled it along you don't have much time to take the reading. I tried to overcome this by taking a lot of repeat readings and the taking an average. I could improve my procedure by redesigning the apparatus. Comments about the reliability of the evidence The results on the graph are closely grouped along a straight line and there is no other line that can be drawn. I think that my evidence is reliable and that my results support the conclusion I have made. The results on the graph so a wide variation. Although a straight line can be drawn which passes through the origin can be drawn, there are others which can be drawn which do not. I think it is likely that the line passes through the origin but it is not absolutely certain. Homan Wan ...read more.

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