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Mechanical Properties of a Meter Rule

Extracts from this document...

Introduction

Mechanical Properties of a Meter Rule.

AIM:

To investigate the mechanical properties of a meter rule via practical experimentation.

INTRODUCTION

The mechanical properties of materials are its fitness and ability to resist applied or external forces. By external force is meant any force outside of a given piece of material which tends to deform it in any manner.

Knowledge of these properties is obtained through experimentation either in the employment of the wood in practice or by means of special testing apparatus in the laboratory. Owing to the wide range of variation in meter rulers it is necessary that a great number of tests are made and that so far as possible all disturbing factors be eliminated. For comparison of different kinds or materials a standard method of testing is necessary and the values must be expressed in some defined units. For these reasons laboratory experiments if properly conducted have many advantages over any other method.

One object of such investigation is to find unit values for strength and stiffness, etc. These, because of the complex structure of the materials, cannot have a constant value which will be exactly repeated in each test, even though no error be made. The most that can be accomplished is to find average values. On account of the great variability in strength of different specimens even from the same material and appearing to be alike, it is important to eliminate as far as possible all extraneous factors liable to influence the results of the tests.

The mechanical properties that I will consider are:

  • Stiffness and elasticity
  • Tensile strength
  • Compressive or crushing strength
  • Transverse or bending strength
  • Toughness
  • Hardness

BACKGROUND KNOWLEDGE:

Study of the mechanical properties of a material is concerned mostly with its behaviour in relation to stresses and strains, and the factors affecting this behaviour.

...read more.

Middle

When the rule was swinging, it sometimes rubbed the side of the table causing the rule to slow down. This will definitely affect my final results.The nail used to go through the holes was not small enough and could have caused friction between the nail and the material causing it to slow down.The stop watch might not have exactly been stopped at the point of 20 oscillations.The distance the rule was moved to be ready for the swing was 0.2 meters. This could have not been accurate for each experiment as I had moved and so the position may seem the same but in fact be different. Using only three holes will not allow me to draw accurate conclusions as it is only three different lengths.

HOW TO RESOLVE PROBLEMS:

  1. I will use a longer nail so that the rule will be kept further away from the table, this should eliminate friction through rubbing.
  2. Firstly I shall get a nail and based on the size of it, drill holes into the meter rule so that it fits easily and properly.
  3. This will be difficult to fix as it is down to human error. So the best way to resolve this will be to pay as mush attention to the experiment in action as possible.
  4. I will stay at the same point to complete this experiment and record results. This should mean that the position in which I let go of the rule will be similar throughout the whole experiment.
  5. I will drill five holes at the points 0.05, 0.1, 0.15, 0.2, 0.25 meters. This should result in enough data to draw accurate conclusions from.

APPARATUS FOR EXPERIMENT 1 (SAG):

  • Clamps
  • 2 meter length wood rulers, 1 meter length metal and 1 meter length  plastic ruler
  • Stand
  • 2 equally level tables
  • Weights (N)
  • Wire or String
  • Dynamic trolley

APPARATUS DIAGRAM:

  • Nail
  • Clamp
  • Stand
  • Tape
  • Stop clock
  • 2 wooden rulers, 1 with 5 holes that shall be made big enough so that the nail can fit comfortably through. The holes will be drilled at the 0.05, 0.10, 0.15, 0.20 and 0.25 meter points.

METHOD:

I will be doing two experiments:

  1. Sag experiment
  2. Compound pendulum experiment

In my first experiment I aim to find out how weight and length affect sag. I will only change one variable at a time. I shall do this by setting up an experiment as seen on the apparatus diagram 1.

First I will attach the clamp to the stand and then the wooden meter rule. This will be used to measure the sag when weight is applied. Then the equally level tables will be moved so that 0.05 meters of either the wooden, metal or plastic  rule of both ends of the rule will be covered (X value on diagram represents the covered length). The stand will be moved to the middle of the hanging rule ready to take measurements. I will then apply string around the middle of the rule. Measurements of the height without any weight will be then taken. One Newton weight will be hung around the string and the difference between the original and new deflection will be taken, then a second weight will be added and the new total deflection measured.

After ten weights are applies and the level of deflection are taken I will change the length variable by moving the tables so that 0.1 meters of the rule will be covered and then redo the measurements. I shall decrease the length of the ruler by 0.05 meters each time about five times.

The experiment will be repeated two more times using different meter length rulers.

For my second experiment I will only use the wooden rule as the pendulum. The experiment shall be set up as seen as on the apparatus diagram 2. I will stick a rule to the side of the table as seen on the apparatus diagram 2. I shall then join the stand to the clamp. Once I have acquired my rule with the holes drilled through it I will put the nail through the hole at the .05 meter point. The nail will then be clamped to the stand.

I will the get my stop clock. I will then move my rule 0.2 meters as seen in the diagram and release it to that it starts to swing. I will then record the time taken for 20 oscillations using the stop clock and take down the times. I shall redo the experiment for each length 5 times to get a better average. I will then move the nail to the next hole and do the experiment again.

X2 on the graph is the point from the nail to the centre of the rule which is the length of the rule.

Health and Safety

Safety is very important in the experiment as certain objects or procedures can be dangerous and can also affect the results. Nothing is particularly dangerous during my experiment. However, I have to ensure that all the equipment is set up properly and that all things are clamped or tied together. This involves checking things like the connection between the nail and the clamp in experiment 2 as well as the retort stand. The stand itself was clamped to the desk to ensure it didn't fall over. In experiment 1 I have to make sure that when the weights are added to the string or wire, that it doesn’t cause the object to break as that could be dangerous.

Fair Testing (Accuracy and precision)

To get an accurate set of results from this experiment it has to be fair. Here are the steps I will take to make the experiment as fair as possible.

For experiment 1:

  • I will make sure the horizontal ruler is straight and not bent as this would cause readings to be read incorrectly.
  • That the weights are added on the middle of the rule.
  • To make sure that I do not move when I am taking the readings so that I get the correct results as much as possible.

For experiment 2:

  • Length of the rule range from 0.25m to 0.45m (measured at regular 0.05m intervals).
  • Timing of oscillations of the pendulum should be taken carefully.
  • The same rule will be used throughout the experiment, so that mass and width etc. will remain constant.
  • Displacement of the pendulum: This will remain constant at 0.20 meters.
  • Air resistance: It is assumed that there is no air resistance and 100% of gravitational potential energy is converted to kinetic energy, and vice versa.
...read more.

Conclusion

  • Measurement of time: Human error as well as reaction times can make a large contribution to any errors in the experiment. Readings from digital stopwatches are accurate to the nearest 0.01s but human error means this reading is unlikely to be accurate.  
  • Size of the displacement: This was 0.2m. Each measurement has an absolute error of ±0.5 centimetre as each measurement is given to the nearest centimetre.
  • Mistakes can be made when making measurements or when choosing the moment start/stop the stopwatch as the rule is released and stopped. This can cause errors, especially if the pendulum is swinging quickly.
  • Random error: These are associated with nearly all measurements and can never be completely eliminated.
  • Friction between the hole and the nail as well as the table and the rule. Sometimes the rule swung diagonally and might have rubbed the table.
  • Air resistance, I did the experiment near some windows and this could have affected the experiment.

I could have carried out some further work on this investigation to extend and broaden my results for example; I could have done more lengths. I repeated the experiment several times and am happy with the averages I got.

A more sophisticated experiment would definitely increase the accuracy in the timings. Light gates would remove the error caused by reaction times as they will accurately time the moment the rule passed over the point to complete an oscillation.

...read more.

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