Cree EnnaChristina Dickens Kristin ForrestLouise Jones
I NTRODUCTION The speed limits on city streets should differ depending on the weather because when it is raining the tires of a car are more likely to slide because there is less friction, possibly causing accidents if the driver does not slow down. One should drive safer on wet surfaces because the tires of a car are more likely to slide on wet surfaces than on dry surfaces, therefore making the force of kinetic friction lower.
P URPOSE People that drive in the rain are sometimes not aware of the possible outcomes. Although the speed limit sign does not change with the weather, one should be aware that their speed should change. To make people aware of hydroplaning.
C OMMON D ANGER - H YDROPLANING Hydroplaning- is when the driver losses control due to not slowing down on wet surfaces. Makes the tires lose contact with the road. Causes a loss of friction, making the driver not able to break or steer at all.
R ESULTS OF HYDROPLANING FROM A PUDDLE OF WATER.
HYDROPLANING CONT’D “Hydroplaning occurs when water on the roadway accumulates in front of your vehicle’s tires faster than the weight of your vehicle can push it out of the way.” ( http://www.engr.pitt.edu/s sc/hydroplaning.html ) Fs= smg
HYPOTHESIS If we test a rubber-wheeled car with a constant velocity on wet concrete, dry concrete, wet asphalt, and dry asphalt, then the rubber on wet asphalt will have a lower force of kinetic friction because the wetness of the surface makes the tires more slick, and the surface is smoother. Basically, it is easier for a car with locked tires to be pushed on wet surfaces.
MATERIALS Calculators for each group member 1 rubber wheeled toy car A level asphalt surface A level concrete surface Stop watch Tape measure or yard stick Chalk 2 Liters of water to wet the surfaces
PROCEDURES Gather materials. Make a chart or table on paper to keep track of the data. The chart or table should include the surface tested, distance of each trial (2 meters), the time it took for each trial on each surface, and the mass of the car. Also an empty column should be on the side to calculate the frictions. Pick your first surface. Measure 2 meters on the surface, and mark the starting line with Point A, and finishing line with Point B with the writing utensil.
PROCEDURES The person doing the timing should be prepared to start the timer as soon as the front tire passes Point A. Pull the switch on the side of the car back to start the car to moving at a constant velocity. To stop the car, push the switch to the front. Hold the car so it will not roll, and put it 4 inches behind the line, to give the time keeper enough time to prepare. Soon as the back wheels pass Point A, the time keeper must start the stop watch.
Observe the behavior of the toy cars speed and then record the test results on the data or chart. After the car has passed point B, the time keeper must stop the timer, and the recorder must record the time. Repeat steps 4-9 for all the surfaces 3 times. Gather supplies, and go to a cool place, so the team members can start to calculate/figure out the results. PROCEDURES CONT’D
Dry AsphaltWet AsphaltDry ConcreteWet Concrete Trial 12.88m/s2.63m/s2.78m/s2.77m/s Trial 22.59m/s2.60m/s2.59m/s2.80m/s Trial 32.71m/s2.75m/s2.60m/s2.68m/s Average2.73m/s2.65m/s2.66m/s2.75m/s The weight of the car is 357.9g =.3579 kg. Dry AsphaltWet AsphaltDry ConcreteWet Concrete Coefficient of Kinetic Friction.22.214.171.124
RESULTS CONT’D F k = k mg Dry Asphalt Wet Asphalt Dry Concrete Wet Concrete Force of Kinetic Friction (Newtons) 2.35 N1.86 N2.39 N2.03 N
In conclusion, the rubber on wet asphalt had a higher force of kinetic friction than the other surfaces. The hypothesis was accurate and we were able to warrant our thesis. Though it was possible for there to not be much of a difference between the four surfaces, the results showed a change in the force.
POSSIBLE ERRORS The car could have gotten off course by the distance between two points. The wind was a factor as contributing to the speed of the car. Different wind speeds depending on location of the trials.
FURTHER EXPERIMENTS Experiments could be tested with… different car different surfaces an obstacle course weights on the car weather variants