The acceleration of a ball down various inclines

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SARANG PALERI        EXPERIMENTAL RESEARCH PROJECT        10G

SCIENCE EXPERIMENTAL RESEARCH PROJECT

THE ACCELERATION OF A SPHERE OVER DIFFERENT INCLINES

PREPARED BY SARANG PALERI


TABLE OF CONTENTS

CONTENTS

  1. Abstract
  2. Introduction
  3. Aim
  4. Hypothesis
  5. Materials
  6. Method
  7. Results
  8. Discussion
  9. Conclusion

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ABSTRACT

In this experiment, I constructed a project to test the change in velocity of a spherical object down a slope, and how that is affected by different inclines. I will record the time a ball takes to get to the bottom of a plank, measuring the times it takes to get to different intervals. The inclines I will be using to roll the ball down are at 2°, 4°, 6°, 8° and 10°. The control will be at 90°, as the only force acting on it is gravity. I will roll the ball down the plank 5 times at each angle, ruling out some random errors. The ball will be a Wilson Championship Heavy Duty 70g tennis ball. The plank can be any length, but it is preferable to use pine wood, as it is soft and is not undulating. The measurements are made with multiple stopwatches, to record times at each interval. The independent variable is change in incline angle, and the dependant variable is velocity down the plank. The acceleration of the ball is determined by further analysing these results.

INTRODUCTION 

My Semester 2 Science Assessment Task requires me to research and investigate an experiment of my own interests and analyse certain scientific principles concerned with this task. The experiment I conducted tests the change of velocity of a spherical object down a slope, and how that is affected by different inclines. The reason I chose this experiment was because I found motion, and how forces induce it, to be very interesting. Possibly being able to mathematically link different rates of acceleration, and maybe being able to calculate the forces exerted on an object during decline is certainly a very enticing prospect, considering this is more useful than many skills I have acquired in my lifetime.

This experiment is technical, as it contains various scientific principles that are used in careers in engineering. Jobs like physics engineers overseeing crash tests to see any flaws in collisions tests, and to interpret results, are available to people with this type of knowledge. This experiment only increases my fascination with this type of science. This experiment also improves certain personal skills, such as the ability to collate, analyse, interpret and conclude. This is another reason I chose this experiment.

Sir Isaac Newton was renowned for many things, among them his studies of refraction and decomposition of white light, calculus, and his Three Laws of Physics, but amid these fine achievements, he was the first to fully explain what gravity is. His inspiration was a falling apple, and he wondered why the apple went towards the ground, and not in any direction. Then he came up with an incredible insight: if this mysterious force that can pull apples from trees can reach to the tallest apple tree, then its range could probably go even further than the atmosphere, maybe to the moon and beyond. His understanding of his force is phenomenal, considering he had no basis of evidence that this force existed, yet his idea developed incredibly. He even went on to create a Law of Universal Gravitation, which suggests that every particle of matter in the universe attracts every other particle of matter with a force proportional to the masses of both entities. Gravity is very important in relation to this experiment.

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The force at work in this experiment is gravity, but friction also contributes, as no friction will result in the ball sliding rather than rolling down the incline. Gravity is a force which is measured with the rate of acceleration it at which objects fall. It is a force created by the presence of mass, and the more mass an object has, the more pulling force it has on everything else to the centre of the mass, which is the centre of gravity. On Earth, the rate at which objects fall is 9.8 metres per second squared, or 9.8m/s2, or ...

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The author’s spelling and grammar is good throughout. However, they have occasionally conflated gravity with acceleration - ‘’ The gravity is affected by the incline angle” – which may suggest to the marker that they didn’t understand the difference between the two (gravity is a constant force exerted by massive objects, causing other objects to accelerate). This is an easy mistake to accidentally make, but one which could cause the loss of several marks. They have also not stuck with scientific conventions throughout – one major example being standard units. The graph used centimetres and centiseconds, which is confusing for the reader. Also, I find it much easier to do calculations when using standard units, making me less likely to make mistakes, which would certainly lose marks. Another lack of convention, although probably not too significant, is the author’s habit of directly addressing the reader - “you need to polish the pine wood plank” – this sounds unprofessional, and I would have rephrased it as: ‘the pine wood plank is firstly polished’. The report is well presented, with clear headings, tables, graphs, and a fairy chronological layout. This makes it much easier to read and mark. However, I would not have included some sections, such as the introductory paragraph about why they have chosen this topic. This is highly unlikely to be a necessary part of a scientific report, other than in some kind of covering letter, so I would never include it unless it is specified in the mark scheme. The author has also included other unnecessary words such as “the rate at which objects fall is 9.8 metres per second squared, or 9.8m/s2, or 9.8 metres every second”. This really is unnecessary! Overall, they have shown a good understanding of how to correctly present a report, but made a few noticeable errors, which may lead to confusion.

They have used their results to come to a conclusion – that the acceleration is proportional to the angle – although mathematical analysis shows that this is incorrect. In fact, the acceleration is proportional to the sine of the angle (a = 9.81sinθ). Further analysis of results would have made this error clear – for example calculating a predicted acceleration based on the assumption that the acceleration was directly proportional to the angle and comparing this with the experimental results. However, as this is a physics experiment rather than a maths one, this may not have had a significant effect on the marks. They have drawn one graph, however, this has only been used to illustrate the fact that there is a relationship between the angle and the acceleration. When we did a similar experiment in college, we were advised to plot a graph of distance against time squared, and use this to calculate the acceleration (2 x the gradient), rather than just stating that there appears to be some correlation. This would also have enabled the author to come to the correct conclusion.

The author has produced a good report about an experiment to compare the acceleration down a ramp of a ball at different angles of incline. They have come to a conclusion and compared this with their hypothesis. However, I would have developed the experiment by using the results to calculate the vertical acceleration due to gravity, comparing this to the true value of 9.81, and using this information to calculate the friction force, for example.