Does Road Surface Affect the Speed of a Car?

Does road surface affect the speed of a car?

Introduction

Cars travel on a variety of surfaces which present a range of different textures from smooth to rough and include dry, wet, icy, gravel and worn textures. Road design is critical to ensure that they are safe, whilst allowing economic driving. These surfaces can affect how fast the car can travel due to the strength of the force between the road and the tyres, defined as friction (Highways Term Maintenance Association, 2011). The Australian Pocket Oxford Dictionary (2004) defines friction as “the action of one object rubbing against another” or the “resistance encountered in so moving” (p. 439). Therefore it can be inferred that the more textured a road is, the greater friction produced and the slower a car will travel (Friction, 2012). Thus a smooth road is critical to ensure that a car can drive economically and not exert too much force to move, which would require greater acceleration and therefore petrol. However a good road is not completely smooth as some friction is essential to ensuring road safety, enabling the car to ‘grip’ the road and stop in a timely, safe manner. Despite good road design, erosion from vehicles as well as rain and other elements can alter the texture of the road and change the amount of friction produced and the conditions for the vehicle (Kane, Tan Do, & Piau, 2010). For example ice on the road can create a smoother surface, whilst road deterioration and potholes create more friction. The purpose of this investigation is to determine the effect the texture of varying surfaces has on the speed of a moving object. This will be determined by analysing the speed of a car on a table top to simulate a smooth surface such as ice; carpet to simulate a smooth surface with bumps like the road; and gravel to simulate a rough surface such as a dirt or deteriorated road. It is hypothesised that the more textured a surface is the slower the vehicle will travel as less friction is created between the tyres of the car and the surface of the road. It is believed that the car will travel the fastest on the table top and the slowest on the gravel.

Method

In order to test the hypothesis, a simple test was designed to compare the rate of travel on varying textures. To ensure fair and accurate testing where the data could be compared, the toy car, the ramp in the form of a binder and the method of timing remained constant in all the tests. The toy car was used to simulate the real car and the ramp was used to ensure the acceleration of the car was the same. In order to determine speed, the car’s distance and time were recorded by using a metric ruler and a timer. This was measured from when the car began the descent to the back wheels of the car, to enable the timer to begin timing easily. The independent variables to test the hypothesis consisted of a table top, carpet and gravel which simulated the different textured surfaces. Each test was repeated three times to increase the sample size and ensure an average could be calculated to ensure a more effective investigation.

The materials used were:

Toy Car

Ramp (binder)

3 Different Surfaces (Table top, Carpet, Gravel)

Timer- stopwatch

Procedure

1. Placed ramp on first surface (carpet).

2. Placed car at top of ramp and held in place.

3. Removed hand from car whilst beginning timing. Allowed car to travel across surface. Stopped timing when car came to a complete stop.

4. Measured distance car travelled from top of ramp to back wheels.

5. Repeated experiment 2 more times on same surface recording information in a table.

6. Repeated experiment on other surfaces (table top, gravel).

Results

Three experiments were conducted which measured distance and time. These measurements were then used to calculate the speed of the car, which was achieved by using the velocity formula (speed= distance/time). As each experiment was repeated three times the average was found using the mean (mean=sum of outcomes/ total number of outcomes).

The car travelling across the carpet was observed to travel at a smooth constant rate which gradually decreased in speed, whilst remaining in a straight line. The table shows the distance, time and speed of the car when travelling on carpet. Each trial produced similar results with the average distance travelled being 46.5cm in 1.38 seconds, thereby travelling at an average speed of 33.7cm/s.

Surface 1 (Carpet) Distance (cm) Time (secs) Speed (cm/s)

Trial 1 46.50 1.28 36.33

Trial 2 47.50 1.45 32.76

Trial 3 45.50 1.42 32.04

Average 46.50 1.38 33.70

The car travelling across the table top was observed to travel quite quickly and not in a linear fashion, tending to veer to one side. This table shows the distance, time and speed of the car when travelling on a table top, a smooth surface. Differences between the distance travelled and the time taken were observed in the trials. The car travelled an average of 90.5cm. In the first trial the car travelled significantly further, in a faster time. The average speed was 46.17cm/s.

Surface 2 (Table Distance Time Speed top) (cm) (secs) (cm/s) Trial 1 95.50 1.74 54.89 Trial 2 88.50 2.08 42.55 Trial 3 87.50 2.06 42.48 Average 90.50 1.96 46.17

The car travelling across gravel moved quickly until it came to a complete stop when becoming caught on the gravel. The car seemed to jolt and bounce when moving along the gravel. This table shows the distance, time and speed of the car when travelling on gravel. The car travelled an average of 37.17cm at an average speed of 36.8cm/s. Differences between the distance travelled and the time taken were observed in the trials. Distance Time Speed Surface 3 (Gravel) (cm) (secs) (cm/s) Trial 1 35.00 1.12 31.25 Trial 2 39.00 0.98 39.80 Trial 3 37.50 0.93 40.32 Average 37.17 1.01 36.80

This table shows the averages from the three experiments. The car on the table travelled the furthest and fastest and this is confirmed in the speed per second. The car on the gravel, although travelling the least distance, had a faster speed than the car on the carpet and therefore was faster when speed per distance was determined. The car on the carpet was the slowest car as determined by the time taken to travel the distance.

Distance Time Speed (cm) (secs) (cm/s) Surface 1 (Carpet) 46.50 1.38 33.70 Surface 2 (Table top) 90.50 1.96 46.17 Surface 3 (Gravel) 37.17 1.01 36.80

According to the graph below, the cars on the carpet and gravel surfaces travelled a similar speed. The car on the table top travelled approximately 10 seconds faster than the cars on the gravel and carpet surfaces.

Discussion The results clearly depicted a relationship between the texture of a surface and the speed an object can travel over the surface, with the car travelling faster on a smoother surface. Friction is the force acting between the tyre and the road surface to create resistance (Friction, 2012). The results show that the more textured a surface the more resistance created and the more force required to move an object. On the table top, the car was able to move freely and almost skid across the surface, whereas the car on the carpet and gravel moved a lot slower as they met with the resistance created, By making smooth roads, cars require less acceleration and therefore petrol to travel, as there is not as much friction preventing them from moving (Kane, Tan Do, & Piau, 2010). However, observations of the car on the table showed it having difficulty ‘gripping’ the surface and moving in a straight line. This was demonstrated in the discrepancy between the results in the trials. The surface was effectively too smooth to create enough friction for the car to drive safely. This is evident on icy roads which have a high accident level, with research attempting to provide ways to measure friction and change speed limit accordingly (Intelligent Vehicle Safety Systems, 2008).

The time taken to travel on the carpet and the gravel was similar. However, this was ten seconds or about twenty percent less than the speed of the car on the table top and therefore was determined to be a significant difference. On the gravel, the car moved in a jerky fashion and was unable to sustain its speed, travelling only 37cm in fast jerky movements because of the friction created which then caused it to stop. The speed and distance included the time taken to travel down the ramp and may have distorted the results. This makes the data difficult to compare with the car on the carpet which continued to move a greater distance, although both cars travelled less distance and at a lesser speed than the car on the table top because of the friction created by their textured surfaces.

Although it is difficult to compare the data relating to the cars on the carpet and the gravel, the test can still be used to demonstrate how friction operates on textured surfaces. One reason for the distortions created could be that the timing was not accurate, due to the short time period and human error; however this should have been accounted for by averaging the test. Due to human error in starting and stopping the timer accurately the test results would also have been affected. This margin for error could have been reduced by increasing the sample size of the test. The timing was begun when the car began travelling down the ramp, a different surface to the one tested, to enable the timer to be more accurate. Whilst this variable was kept the same in each of the tests, it meant that the speed over each of the surfaces was not entirely reflective of the speed over them and included the distance of the ramp. Because of the short distance travelled by the car over the gravel, this appears to have affected the accuracy of the data. Starting the timing at the end of the ramp would have made the data more reliable.

Conclusion This investigation was successful in achieving its aim to determine how the texture of a surface impacts on the speed of a car, showing the smoother the surface the faster the car will travel. The hypothesis that the more textured a surface is the slower the vehicle will travel as less friction is created between the tyres of the car and the surface of the road was partially correct as the car on the smooth surface, the table top, travelled the fastest and was significantly faster than the cars on the gravel and the carpet. The slowest speed was recorded by the car on the carpet, not the gravel.

The investigation could be extended by analysing how surface friction changes when the surface is wet to test the impact wet roads have on vehicle control. The investigation could be improved by increasing sample size to reduce human error and by expanding the range of surfaces and cars used to gather more data on how friction works.

References

Australian Pocket Oxford Dictionary. (2004). Melbourne: The Bookmaker International Ltd.

Friction. (2012). Retrieved April 1, 2012, from Skwirk: http://www.skwirk.com.au/p-c_s-4_u-308_t- 755_c-2841/friction/nsw/friction/force-and-motion/force-and-gravity

Highways Term Maintenance Association. (2011). Road Surfacing: Why Does It Matter? Retrieved April 2, 2012, from HTMA: http://www.htma.co.uk/smartweb/hot-topics/road-surfacing

Intelligent Vehicle Safety Systems. (2008). Road Friction Estimation. Retrieved April 2, 2012, from IVSS: http://www.ivss.se/upload/IVSS_2004-17750_final_report_070608.pdf

Kane, M., Tan Do, M., & Piau, J. M. (2010). On the Study of Polishing of Road Surface under Traffic Load. Journal of Transportation Engineering, 136(1), 45-51.