Prove that "Frictional Forces are Surface dependant".

We were given a coursework question asking us to prove that “Frictional Forces are Surface dependant”. We were asked to prove this. I have therefore thought of several ways to do so;

I thought of throwing different objects across different surfaces.
I thought of using an elastic band to throw a block of wood, 4.5cm X 4.5cm x 4.5cm, across a certain surface with a certain length; 1.25 metres. I thought of making the surface as my independent variable and the block of wood as my dependant variable.
I also thought of performing the above procedure but instead of using different types of surfaces, I thought I would use several types of blocks of different material, but all of the same weight. And using the rubber band, throw it across a surface of ceramic.

I have decided to merge the two ideas, and came up with the following idea and procedure;

My idea was that I could use two 5cm x 5cm x 5cm blocks, one of wood, and the second of plastic foam. I intend to try them on several different types of surface; wood, ceramic, marble, carpet (with a certain thickness which I shall state later on), and glass. All of which are 1.00metres (100cm) in length. I intend to use the surfaces as my independent variables, and the blocks as my dependant variables. I intend to prove that the type of surface, makes a lot of difference in the velocity (speed) of the block, and that due to friction and the surface, the distance covered, and the time consumed change according to the type of surface, and whether it has a high frictional surface or a low frictional surface?

My procedure: I thought that I would implement my idea so as to prove the relationship between the contact surface, and the frictional force.

Firstly, I would like to refer to the information that I have gathered so as to enable me to place a procedure that is correct and which I guarantee that it will provide me with some reliable results.

Friction is the property that objects have which makes them resist being moved across one another. If two objects are placed one on top of the other, the top object can be lifted without any resistance - except that of gravity. But if one object is pushed or pulled along the surface of the other, there is a resistance caused by friction. Friction has many important uses; it makes the wheels of a locomotive grip the rails of the track. It allows a conveyor belt to turn on the pulleys without slipping. Without friction, we would not have been able to walk on the pavement; we would have kept on slipping! That’s why it is hard to walk on ice; it produces friction that is less than the pavement, and therefore causes us our shoes to slip. Friction also has disadvantages; it produces heat which causes objects to wear; have you ever looked at the soles of shoes which you have been wearing for 2 years, and the soles of brand new shoes? Observe the difference! Several layers of your shoe’s soles have worn away – due to the friction of the shoes on the pavement, this is why lubricating oils are used to fill in the gaps between moving machinery parts. There are three main kinds of friction: Sliding or kinetic friction; this is produced when two surfaces slide across each other, like when a book moves across a table. There is also rolling friction, which is the resistance produced when a rolling body moves over a surface. E.g.: the friction between a car tyre and the street is rolling friction. Fluid Friction/ Viscosity are the third type of friction. It is the friction between moving fluids or between a fluid and a solid. “Thinner fluids have less viscosity than thicker fluids, and usually flow faster”. E.G: erosion of rocks in the rivers by running water.

The law of friction: The basic law of friction states that the force needed to overcome friction is proportional to the total perpendicular force pressing one surface against the other. E.g.: when the weight of a box being pulled across the floor is doubled, the force pulling the box must be doubled. The ratio between the weight being pulled/pushed, and the force required is called the coefficient of friction.

The value of the C.F depends on the type of surfaces moving against each other.

Friction:

Friction is the resistance that a moving object meets when it is in contact with another object. It is a force that converts a moving object’s kinetic energy (energy of motion) into other forms of energy, such as heat and sound. This process slows the object down. Friction can be reduced – for example, by lubricating the surfaces of the two objects in contact. Friction can be useful, too. It is the force that makes a car’s brakes work.

E.G.: When a match is struck, friction provides the heat that causes phosphorus in the match head to ignite.

Coefficient of Friction:

The coefficient of static friction is a measure of how much force must be applied to an object to overcome friction and set it moving across the surface of another object. It varies for different pairs of objects. The coefficient of kinetic friction describes how much force must be applied to overcome friction between the two objects once one of them is in motion.

Theory

Suppose you place a book on a rough desktop. The weight of the book produces an equal and opposite reaction force; R from the surface. The force you need to apply to make the book begin to slide is independent of its area of contact with the surface but is proportional to R. The force you need to apply is related to the weight of the book (equal to R) by the coefficient of static friction, symbol μ. If you try to push the book sideways with a force that is less than μR, it is cancelled out by a corresponding frictional force, and the book does not move. As you increase the force, the frictional force increases too. The frictional force will continue to increase as a reaction to you pushing the book until it reaches μR, which is the limit of static friction. If you increase the force beyond this limit, the book starts to move across the surface.

The value of the coefficient μ is determined by the two adjacent surfaces and is not a strict constant. Its value varies from about 0.15 to 0.6 for most dry and fairly smooth surfaces. It depends only on the nature of the two bodies, and not (as might be supposed) on the area of contact between them. In other words, if you have two equally heavy books made from an identical material, you need to push just as hard to make them move, even if one book is large and thin (has a large cover) and the other is small and fat (has a small cover).

Once an object is moving steadily across a surface, its movement is opposed by a kinetic friction force. This force has a value lower than the limiting force of static friction, meaning that a greater force is needed to start an object than to keep it moving. This is described by a coefficient of kinetic friction, which is always less than the coefficient of static friction for two objects.

Formula

Force needed to overcome friction (Fmax) = coefficient of static friction (μ) × force keeping body at rest (R).

Since both forces are measured in Newton (N), the coefficient of static friction is simply a number with no units.

Example

A car of mass 1,000 kg has broken down on a road made of asphalt. If the driver has lost the keys and the brakes are locked on, what force is needed to push the car? The coefficient of static friction between rubber and asphalt is 0.60, and the acceleration due to gravity, g, can be taken to be 10 m s−2.

Solution

The car resists any attempt to move it due to its weight, which is equal to its mass multiplied by the gravitational acceleration g.

R = m × g = 1,000 × 10 = 10,000 N

Fmax = μ × R

Fmax = 0.60 × 10,000 N = 6,000 N

A force of 6,000 newtons (N) is needed to push the car.

Therefore, with reference to the information stated above, I have planned the following procedure and equipment:

Apparatus:

1 Block of wood with measurements 4.5cm X 4.5cm X 4.5cm (volume= 4.5cm3). (dependant Variable)
1 Block of plastic foam, 4.5cm X 4.5cm X 4.5cm (volume = 4.5cm3). (dependant Variable)
1.00metres of: ceramic, carpet (2mm thickness), carpet (7mm thickness), marble, wood, and glass. (independent Variables)
Stopwatch.
Tape-measure.
Elastic band (which reaches a length of 85cm when stretched).
Cello-tape.
Scissors.
A marker pen.
An electronic weighing scale.

Procedure:

I will measure the sides of the cube to ensure that it is exactly 5cm3.
I will then measure 100 cm of each surface, and stick the cello-tape across the length of each.
Using the marker pen, I will place a mark on the tape every 10cms.
Next, I will measure a distance of 5cm (equal to the size of the cube) from one end of the surface, and also on the side opposite to it; 5cms extra to the 100 of the surface, 15 extra on the right hand sides, and 5cm extra on the left hand side. This is the space I will place the cube in before catapulting it across the surface.
I will then measure the width of the tape, and stick the exact amount of the rubber band underneath it, one side of the rubber band at a distance of 10cms apart.
Then, using the rubber band that has been stuck to the surface, I will place the wooden block in between the rubber band, and pull the rubber band back (with the cube) to a distance of 15cm. (the 15cm I have added previously).
I will hold the stop watch in one hand, while holding the stretched rubber band and the wooden block in the other hand. As soon as I let go of the rubber band, I will start the stopwatch.
I will observe the block fly across the surface, and I will have my finger on the stop button in the watch, and that’s to stop it once the block reaches the end of the surface, or if it stops in the middle of the surface. In which case I will take a reading of the distance covered and not down the time in my table.
I will repeat this experiment 3 times, and that’s to guarantee the reliability of my results, and also to graph the average of my results which should be more accurate than just one trial.
I shall repeat the above procedure for the different types of surfaces and for the different cubes.

I intend to take some safety measures; I will place an extra piece of tape on top of the tape already holding the rubber-band in place, and that is to ensure that it will not fling out of place. I also intend to place two 1metre rulers on either side of the practical area, and that’s to prevent the block of wood from flying off course. I also have several other rubber bands of the same thickness and length of the rubber band being used (from the same box), and that’s in case the rubber band used breaks. ...

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I intend to take some safety measures; I will place an extra piece of tape on top of the tape already holding the rubber-band in place, and that is to ensure that it will not fling out of place. I also intend to place two 1metre rulers on either side of the practical area, and that’s to prevent the block of wood from flying off course. I also have several other rubber bands of the same thickness and length of the rubber band being used (from the same box), and that’s in case the rubber band used breaks. I have also placed a piece of tape on the surface; marking the end of the 100 cm, and that is to enable me to see exactly when the block has passed the 100 cm, enabling me to stop the stop-watch in the right time, resulting in some reliable results.

My theory:

I believe that my plan shall be quite good and that it shall enable me to obtain sufficient results which are reliable. My theory is that the rougher the surface, the higher the friction, and consequently, the more time is consumed for the block to reach the markers. While the smoother the surface, the less the friction, and consequently, the less time is consumed.

My Prediction:

I predict that the marble shall prove a very good surface close to ice which will enable the block to shoot across it like a bullet fired from a gun, this is because the marble surface is quite smooth, and also quite slippery, which indicates a low level of frequency. Yet, I predict that the 7mm thick carpet and the wooden surface shall prove to have very high friction, and thus, the block shall not be able to cover the complete distance of 1.00metres on that surface, especially with the force applied. This is of course with reference to the data stated above.

I have placed this plan according to a test we have previously observed regarding friction, as we have studied in class friction and its effect. This gave me the idea that I need an equal amount of force to push the block each time; and if I was to apply this force by hand, how could I guarantee that the force applied each time is equal? The test has to be fair! So I decided to follow the above procedure, using a rubber band which is stretched to a certain extent (15cm), this will guarantee that the force applied each time is equal. I have also thought of extending the length of the surfaces used to 2.0 meters, but after my preliminary test, I found that 1.00 metres are sufficient, and that they will enable me to prove my theory and prediction. I have modified my original version which I have followed in my preliminary test, and that’s to guarantee the reliability of my results.

MY PRELIMINARY TEST:

I should have placed this test earlier, but I was unlucky enough to be unable to find a good place for it, so I thought that the best place for it would be here; at the end of my planning, and that is to link it with my observations and “Obtaining”.

For my preliminary testing, I decided to try out a procedure which would enable me to obtain some reliable results; after deciding upon the investigation I intended to perform, I decided to use a rubber band to apply equivalent forces each time in my original investigation. I also decided to try out my preliminary using a block of wood with a volume of 4.5cm3. I decided to try my preliminary on ceramic as it was the easiest to start with; so I placed two 1 metre rulers at a distance of 10cm apart. I placed them both with their “0” ends towards my side, and the 100cm marker at the other end. I then “stuck” the two ends of the rubber band (25cm in length) one side at either ruler. I placed a piece of tape at the end of the surface, linking the two “100cm” marks together and showing me the end of the 1 metre distance. I then measured out 15 cm from the “0cm” markings, and placed a piece of tape in between the two rulers. I then placed a block of wood with volume 5cm3 in between the two “arms” of the rubber band, and pulled it with the rubber band to the extent of 15cm (until the marking), I then let them go, and the block of wood was catapulted towards the other end (towards the 1metre marking). I took a record of the time consumed, and found that it covered 60 cm and stopped. That took it a time of 0:32 sec.

Therefore, according to this preliminary, I have decided upon using a distance of 1.0 metres; since the smoothest surface with the least friction (in my opinion) did not allow the block of wood to cover more than 60cm, I do not expect any of the other surfaces to provide a force which will be less than the force applied by the rubber-band. I have therefore drawn up the procedure stated above; this is because I believe it to be the best procedure I could follow, and implement the steps within. That is of course with reference to the safety measures I have taken, and also because I am familiar with most of the equipment, and could therefore tackle their side effects. I also hope that this procedure will enable me to gain the best results possible.

The source of my idea:

We have previously performed a semi-coursework which consisted of the following: we were required to prove that an object accelerates as it descends and gets closer to the ground due to the gravitational pull upon it. To do this, we were given a measuring cylinder full of 1liter of motor oil. We placed 10 markers which were equidistant (5cm3). We then dropped 10 ball bearings; one at a time. Each time, we started the stop watch as the ball started to descend, and stopped the watch at the next marker each time. E.g.: the first ball, the stop watch was stopped at the first marker. The second ball at the second marker, the third at the third marker…etc. we then obtained the ball bearings by the aid of a powerful magnet, and repeated the investigation. We then averaged the time and graphed our results.

Before performing the original investigation, I decided to perform a preliminary test which I have stated the results and consequences of previously. I then intended to perform the investigation, implementing the procedure I have drawn up for myself.

I then found out that this procedure would not provide me with a “fair” test. So I decided to alter my plan slightly; instead of timing how long it took for the block to stop, I could count how long it took for the block to pass each marker (10cm). I would therefore have to decrease the amount of surfaces I intend to use to two (2). This is because I intend to make it a fair test, and also; to save me some time. Therefore, I will catapult the block 10 times, note down the time it took to reach each marker in turn.

I started off by getting the tools and materials required and placing them in a small, neat pile on my work bench. In doing so, I found that the surfaces were not portable (mobile), and I would therefore have to go to each surface wherever it is.

First of all, I started by cutting up 230cm of Cello-tape (aided by the 1meter ruler) and then splitting that into two equal pieces (strips); each strip with a length of 115cm. using the marker pen, I placed a mark on the tape every 10cm, (the “0” mark starts after 15cm);

I intend to use only two surfaces; ceramic & wood. This is to spare me some time to perform repeats and to compare the results using the two blocks. I will perform the experiment with the two blocks as stated in my primary plan. All that has changed is the method of recording time; instead of recording the time each block took to completely stop on each surface, I will measure the time taken for it each time to cover the distance between the markers; e.g.: in the first catapult, I shall stop the watch when the block passes the first marker indicating (10cm). In the second catapult, I will stop the watch when the block passes the 2nd marker, indicating 20cm, and so on, similar to my source of idea and procedure. I also found that the process was too time consuming, and I therefore decided to perform the investigation with only one block, the block of wood.

After marking every 10cm on the tape, I decided to start with the ceramic surface, so I went to the ceramic surface and placed one of the two strips of tape along the length of one side of it. I then measured a distance of 20cm from the tape, and stuck down the second strip of tape; the two tapes are parallel with a distance of 10cm in between them. I then cut the rubber band from one side, which gave me a long strip of rubber. At the ‘0cm’ mark, I stuck one “arm” of the rubber; I then stuck the other arm at the opposite “0cm” mark (one arm at each tape). I then placed the wooden block in the rubber band’s “Lap”; between the two arms, and pulled them (the rubber band and the block). As soon as I let go, I pressed the start button on the watch. I then stopped the watch once the block had passed the 1st mark. I then repeated the procedure, but this time stopped the stop-watch as soon as the block passed the second marker. I kept on doing this, each time stopping the stopwatch at the next marker. After finishing doing so, I did my repeats, repeating this process all over again – 3 times – until I had got three readings for each marker.

I then repeated the whole process, but this time, I did it with the wooden surface; I took the marked tape I had used in the previous experiment, did my measurements, and stuck everything down as I had done in the previous surface; marble. I then repeated the process as I have done in the previous surfaces.

I have included below a table containing my results, and a full report regarding what actually happened:

After observing the results I have obtained and placed in the above table, and with reference to my notes and annotations which I have produced during the investigation, I found that the block of wood, would only reach a certain distance, that is of course due to the thrust (force applied), but as I have followed my initial plan step by step, altering only what I have stated previously, I could not alter anything else or make any extra modifications. I was therefore stuck with the rubber band I had started with. As is noticeable; in the first table which is for the marble, the block stopped at the marker indicating 70cm, and did not proceed. While in the second table which is for the wooden surface, the block reached the mark which indicated 60cm, and did not proceed. This I shall analyse in the following section and state the reasons for.

Unfortunately, this investigation was not easy; this is mainly because not every time I let go of the rubber band did the block reach the required mark, and before stating that the block stopped, I did and re-did the experiment to ensure that the block could not indeed reach that level (mark). Sometimes I would also let go of the rubber band before starting the stop-watch. I have therefore tried my best to obtain and use the most reliable results possible. I have followed my procedure step by step, and I have also used the equipment I am most familiar with, and that’s to enable me to cope with and provide the best results attainable by the aid of this equipment. I hope that these results are sufficient, and that they will enable me to prove my theory and prediction.

After performing my investigational experiments, and identifying the most obvious of the information and mistakes, I intend to proceed to analyzing my results, procedure and implementation of it.

Below are the graphs that I have drawn up based upon the average times, and the markings.

analysing the above graph which is the graph for the Marble surface; we can notice at a glance that there is what resembles a straight line. With reference to my physic’s knowledge, I know that a straight line starting from the 0, and extending at an angle of approximately 46o, indicates uniform acceleration. We also know that a line graph which starts somewhere along the Y-axis, and extends diagonally towards the X-axis resembles uniform retardation. Looking at this graph, it resembles uniform acceleration, but as it is not a V-t graph, it actually resembles uniform retardation. We gather this logically because more time is consumed by the cube, and that’s for it to reach the following point. If we look at it scientifically; we could observe that the Y-axis is a time scale, and the higher up we go – the more time is consumed 9on the graph), and the X-axis resembles the “checkpoints” or “marker-points” , and as we go further eastwards, we cover a greater distance, and by covering greater distances, force wears away, and as we have started with a pushing force that “unbalanced” the opposing force, as the force wears off; is consumed, the forces start to balance, until the force completely wears off, and the opposing force has little resistance and is greater than the pushing force, which causes it (the block of wood) to eventually stop, leading it to a state of uniform velocity where acceleration equals Zero. This therefore causes the time consumed to increase. This is because though the acceleration has stopped and returned to a uniform state in which it equals Zero; time is still ticking away, and consequently, more time is consumed!

I then studied the above graph for some time, and found that it was exactly the same as the first one. It resembles the trend of uniform acceleration in a V-T graph, but since these graphs are not V-T, and are Distance X time, the observation is different. The graph resembles a straight line, curving towards the end which indicates that the block is slowing down. This proves my theory, yet it also shows us that the speed /acceleration of the block are decreasing, which means that the opposing force seems to balance the pushing force, eventually overpowering it, causing it to slow down until it eventually stops, reaching a state of uniform velocity which is equal to zero.

After analyzing the results, I found that there was a slight stability in the results obtained in the repeats. I have also noticed that the recorded times for the block’s passage by each marker or “checkpoint” each time. There seems to be a pattern in the graph as the results when linked with each other, provide a straight line which is quite rare to obtain.

Closer analysis showed that the first graph which was for the block’s “sliding” across a marble surface had a line which was straight all the way to the end, while the second graph which was for the sliding of the wooden block along a wooden surface starts off straight, but towards the end, curves upwards slightly. This incline indicates a sudden change in the balancing of the forces. And since the incline is upwards, this suggests that the pushing force has been out-powered by the opposing force. I believe the situation to be so because the upwards incline suggests the increase in time consumption, which indicates that the pushing force which started off quite powerful and slightly stronger than the opposing force, enabling it to reach this point. But the force has been worn off in the long journey, and eventually, the acceleration of the block starts to decrease which indicates retardation. This retardation results in a weakening of force, which causes the pushing force to weaken, consequently, it is over-powered by the resisting/opposing force.

This proves my theory as I have theoretically stated that:

The rougher the surface, the higher the friction, and consequently, the more time is consumed for the block to reach the markers. While the smoother the surface, the less the friction, and consequently, the less time is consumed.

With reference to my results, we can see that on the marble surface, the block of wood reached the “70cm” marker, that is, with the force that was applied. While the block of wood did not exceed the ‘60cm”marker on the wooden surface. This suggests that there was a greater opposing force provided by the wooden surface than that which was provided by the Marble surface.

Closer studying to the surface enabled me to gather that the marble surface was indeed slightly smoother than the wooden surface. Scientifically, I would say this because the marble is one smooth surface, but the wood consists of fibres (I saw this using a magnifying glass), which cause the block to, slow down. I also thought of looking at the base of the block (I have been catapulting it on the same side), I found it was slightly darker than the other faces (of the cube) and that there were some splinters of wood sticking out of it which were not there when I started. This shows that there was indeed friction and that there certainly was some heat produced.

Also, the block was made of the same kind of wood as that of the surface, which could be the cause of the great friction. It’s like when we push our two hands upon each other, and try to slide one of them, it’s quite hard! You will eventually succeed, but by that time, you will have exerted a lot of energy, and anyway, you are applying more force every second by your muscles, and that’s to complete the task. But place your two hands “the same two hands!) On an icy surface; they will slide pretty easily, and you will probably find a hard time trying to stop them. This is exactly the case, the wooden block is pulled tightly towards the wooden surface by gravity, and as the two surfaces are from the same material, they will stop after a short time. This is because they are of the same material, they are pulled close together by gravity, and the force applied is not renewed. While when we placed the block of wood on the marble surface, we succeeded in making it reach a farther marker than on the wood. This is mainly because the marble surface is quite smooth, (it resembles ice in a way), and has no fragments sticking out f it (splinters), this makes a pretty slippery surface for the block of wood.

I have stated previously that gravity plays an important role in this investigation; I have stated that the pull of gravity on the surface and block, cause them to stick close to each other, which plays an important role as this increases the friction, and consequently affects the terminal velocity (speed) of the block. We also know that the mass (size/weight) of the block determines the size of the gravitational pull on the block. We also know that “acceleration = Force X Mass”. I have therefore decided to weigh the block using an automatic scale, and found that it weighed: 50grams.

I have also referred to the following Formula:

F1>F2 Then movement is present in the direction of F1.

F1=F2, Then there is no motion/movement.

In this formula, F1 indicates the force applied, “the pushing force”, while F2 indicates the “opposing force”.

The above graphs are both for the velocity of the block of wood on both of the surfaces. To find the velocity, I had to refer to a formula which linked the speed with the distance and the time; Velocity = Distance / time. With reference to this formula, I managed to calculate the velocity of the block of wood on each of the surfaces.

By observing the first graph, which is for the marble surface, we notice that the curve is slightly off-line, which indicates a problem with the investigation. But overall, it represents a curved line which starts at a low speed, and gradually the velocity increases, reaching its maximum as 78cm at the 4th marker (40). It then starts to slow down, but gradually. Unfortunately, I could not apply any greater pushing force on the cube so as to gain more results by it reaching the 100cm marker, because it would then have been an “unfair” test. We therefore notice that the graph (line) does not extend to the Zero line, which it should have done theoretically.

We then observe the second (or in this case the 4th) graph, which is for the velocity of the wooden block on the wooden surface. We notice that the line (curve) is somewhat smoother than the other. If we looked at it more closely, we notice that the left side of the curve is a straight line directly from the zero, (indicated by red dotted line). The line reaches it’s maximum at 80cm at the 4th marker (40). This means that both the surfaces do not have any dramatic effect upon the block of wood until the 4th marker. This is of course with the exception of the maximum velocity of both surfaces which depends upon the material itself.

Looking past the 4th marker, we notice that the 1st graph (3rd) starts to go off-line slightly which could be an anomaly, or could be due to one of the problems I intend to identify in my evaluation. But then, the line goes off at a straight line at an angle of approximately 195o. That is of course with reference to the theory that the line shall stay straight until it reaches the 0 line, which indicates a non-velocity state. This means that the line would probably have had to reach a 200 marker. But of course, there seems to be an anomaly as the line is not 100%straight. On the 2nd graph (4th), we notice that the line, after the 4th marker, seems to incline downwards, towards the 0 line on the X-axis, though, it is slightly steeper than the first graph, as it seems to be inclining at an angle of approx. 200o.

This indicates that the marble surface is a less frictional surface in comparison with the wooden surface. I have gathered this because the line of the wooden block after the 4th marker is steeper than the line for the marble surface which is after the 4th marker. This mean that if we were to observe the graphs theoretically, we would find that the line for the marble surface would cover a greater distance, approx. 200cm (2.00m), while the steepness of the line for the wooden surface indicates that it would touch the zero line (X-axis) sooner than the line for the marble surface, I believe that the line for the wooden block will cover approx. a distance of 150cm (1.5m).

With reference to the above information, I gather that the wooden block shall cover a greater distance on the marble surface than on the wooden surface, provided that the force applied is sufficient enough to enable the block of wood to cover the distance assigned. This is of course due to the high friction of the wooden surface which exceeds the frictional force of thee marble surface noticeably.

With respect to the above statements, there is one contradiction; the maximum speed covered by the block on the wooden surface exceeds the maximum speed covered by the same block on the marble surface. That is by several centimetres (the unit of measuring velocity in this assignment). I have tried to find a scientific explanation for this phenomenon which outlaws any of the conclusions I have reached, but I was unsuccessful.

We therefore conclude that the block of wood moved more smoothly on the marble surface. This proves my theory which stated that; the rougher the surface, the higher the friction, and consequently, the more time is consumed for the block to reach the markers. While the smoother the surface, the less the friction, and consequently, the less time is consumed. I therefore gathered that the “Rougher” the surface, the more the opposing force, and consequently, the more friction and heat are produced. Yet, the “smoother” the surface, the less the opposing force, and the less the friction and heat resulted. This also proves my prediction which was based on the information I had gathered previously and which stated: I predict that the marble shall prove a very good surface close to ice which will enable the block to shoot across it like a bullet fired from a gun, this is because the marble surface is quite smooth, and also quite slippery, which indicates a low level of frequency. Yet, I predict that the 7mm thick carpet and the wooden surface shall prove to have very high friction, and thus, the block shall not be able to cover the complete distance of 1.00metres on that surface, especially with the force applied. This is of course with reference to the data stated above. We also gather that friction is the property that objects have which makes them resist being moved across one another. If two objects are placed one on top of the other, the top object can be lifted without any resistance - except that of gravity. But if one object is pushed or pulled along the surface of the other, there is a resistance caused by friction.

With reference to the information I have gathered; the value of the C.F depends on

The type of surfaces moving against each other.

This relates to what I have stated previously regarding the type of surface, and for which I have provided an example using the hands. I have concluded the above after referring to detailed scientific information and also after closely analysing the results and evidence I have obtained. I therefore believe that I have done what was asked of me and that I have performed the task I was assigned and have succeeded in proving my theory, prediction and procedure to be accurate, correct, and reliable.

Also by referring to the second graph which is for the wooden surface; we notice that the straight line curves towards the end (upwards), which suggests a sudden change in the balancing of the pushing and the opposing forces. Scientifically, this suggests retardation, and the curve indicates that the block suddenly started to lose the force applied to it. It started off with uniform retardation, and then suddenly started to stop several seconds faster than when it had started. This means that the wooden surface is slightly “rougher” than the marble surface, and that it provides friction that is slightly more (higher) than that provided by the marble surface. I believe that this is what I was asked to prove.

Below is a diagram showing the forces available in this investigation:

I have performed this investigation to a good standard, and believe that the results I have obtained are good enough and are sufficient as they have enabled me to prove my theory, prediction and procedure. They have also enabled me to prove what was asked of me.

I wish to annotate the procedure I have followed because though I have performed it to a good standard, there are still some flaws in it and I still believe that it could be performed at a standard that would be better, well, no body is perfect.

After finishing my investigations, I found that the block was slightly darker than when I started, this indicates that the surface may well not have been clean. This indicates that there were dust particles available on the surface, and as dust particles are sharp (when observed under the microscope) and have rough edges, it is therefore believed that they would cause a big difference in my results as their rough surfaces interfere with my investigation. I believe this because as the wood block is sliding across the surface, I am investigating the effect that the surface itself has on the terminal velocity of the block. With the presence of sharp-edged dust particles in the middle (between the surface and the wooden block), more friction and heat are acquired through the dust particles, which slow down the block moderately. Therefore, if I was to perform this investigation once again, I intend to guarantee the cleanliness of the surface I am working on.

Another thing was the presence of wooden splinters small, but seen, on both the wooden surface, and the side of the block I was working on. These splinters most certainly would have interfered with my investigation and results. I believe this because the splinters would be between the surface and the block, causing more friction, and therefore slowing down the block, thus affecting the acceleration of this block, and giving me inaccurate results. The next time, I intend to ensure that the surface lack any external effects which might alter my investigation, for the worst.

Something else was that the marble was not just one straight block which would have been quite suitable for this particular investigation. In fact, it was a working bench, and it was made up of several tiles. (The tiles had a smooth surface without any drawing or grooves on). The small cracks between each tile might well have affected the velocity of the block; causing it to slow down before reaching the desired marker. This would have given me some false results and would have caused the time consumed to be several seconds more than what it actually should have been. If I was to perform this investigation another time, I would try my best to use one whole tile of marble instead of several tiles, and this should provide me with some results which are more reliable.

I was using my naked eye to stop the watch once the block passed the marker, so I could possibly have stopped the watch before the block actually passed the marker, or I could have started the watch several “tierces” (1 hundredth of a second) after letting go of the rubber band, which means that the timing was not 100% accurate. If I was to perform this investigation again; I would use one of the following: A) - Light gates, B) - Interrupt Card, C) - Or a ticker timer. Any of the above methods would provide me with some reliable results which would be more accurate than the results I have obtained.

By observing Graph A; the graph for the marble surface, the result for the 40cm marker is slightly of the line, but as I said previously this could well be due to the dust particles which were on the surface, or could also be due to the splinters available on the faces of the wooden block. It could also be due to my method of timing, either way, if I was to perform the investigation another time, by altering the errors I have identified previously, I look forward to some results which are anomaly-free, and that also contain no errors.

By observing Graph B; the graph for the wooden surface, we notice that the straight line curves towards the end, which suggests a sudden change in the balancing of the pushing and the opposing forces. Scientifically, this suggests retardation, and the curve indicates that the block suddenly started to lose the force applied to it. It started off with uniform retardation, and then suddenly started to stop several seconds faster than when it had started. This means that the wooden surface is slightly “rougher” than the marble surface, and that it provides friction that is slightly more (higher) than that provided by the marble surface. I believe that this is what I was asked to prove.

We also notice that there is a semi-anomaly; the result fir the 30cm is slightly out of line, it is slightly lower than where it should be, this could be due to one of the external factors that I have stated previously, or it could be due to some other factor that I have been unable to identify using the tools available to us.

I have tried my best to identify the factors which could have affected my investigation and consequently, my results. That is of course with the equipment provided to us. If there are any other factors which I have failed to identify, that would be because of the tools provided to us. Though, I doubt that there are any other factors that could be identified using other apparatus.

Overall, I believe that I have performed this investigation to a good standard, and that I have succeeded in proving my theory and prediction. I also believe that I have done what was asked of me, and proved that frictional forces are surface dependant. I have proved it with reference to my knowledge, to external, advanced information, and also with reference to my investigation. Though I have performed this investigation to a fairly good standard, I believe that it could be better and that by performing this investigation again after altering the errors I have stated above, I would be able to provide sufficient evidence and proof which is undoubted and accurate by 99%. I say this because no matter how hard I try, the equipment provided to us are not that advanced, and therefore, there will always be better methods with results which are more accurate than what I have obtained. I have therefore performed this investigation as best as I could, and hope that the results and information I have gathered are sufficient.

Karim Hatem Abou Ahmed

Year 10

GCSE Physics

Science Department