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Physics and Car safety
Friction Lab

PURPOSE: To see and prove what type(s) of surface are best for cars to drive on.
 
MATERIALS:
- block with weight inside and rubber bottom
- force scale
- wood surface
- sandpaper surface
- cement surface
- stopwatch
- measuring tape
 
PROCEDURE:
1)Measure a distance of one metre.
2)Slide the weighted box with the rubber bottom across each surface (wood, cement and sandpaper) 5 times.
3)Time each slide.
4)Read the force required to pull the 5 kg box.
5)Find the velocity of each trial.
6)Find the acceleration of each trial.
7)Calculate the coefficent of friction for each surface using the average force.
 
Results:
Wood Surface

Trial #
Time
Velocity
Acceleration
Force (kg)
Force (Newtons)
1
5 s
0.2 m/s
0.04 m/s*
1.85
0.074
2
5 s
0.2 m/s
0.04 m/s*
1.70
0.068
3
4.5 s
0.2222 m/s
0.0494 m/s*
2.10
0.10374
4
4.7 s
0.2128 m/s
0.0453 m/s*
1.90
0.08607
5
4.6 s
0.2174 m/s
0.0473 m/s*
2.20
0.10406

Average

4.76 s

0.2105 m/s

0.0444 m/s*

1.95

0.087174

Cement Surface

Trial #
Time
Velocity
Acceleration
Force (kg)
Force (Newtons)
1
3 s
0.3333 m/s
0.1111m/s*
3.1
0.3444
2
3 s
0.3333 m/s
0.1111 m/s*
3.2
0.3555
3
4.5 s
0.2222 m/s
0.0494 m/s*
3.25
0.16055
4
3.6 s
0.2777 m/s
0.07716 m/s*
2.95
0.2276
5
3.15 s
0.3175 m/s
0.1008 m/s*
3.3
0.3326
Average
3.45 s
0.2968 m/s
0.08992 m/s*
3.16
0.2842

Sandpaper Surface

Trial #
Time
Velocity
Acceleration
Force (kg)
Force (Newtons)
1
3.46 s
0.2457 m/s
0.0710
4.2
0.2982
2
3.3 s
0.2576 m/s
0.0781 m/s*
4.57
0.3569
3
2.86 s
0.2972 m/s
0.1039 m/s*
4.55
0.4727
4
2.67 s
0.3184 m/s
0.1192 m/s*
4.70
0.5602
5
2.81 s
0.3025 m/s
0.1076 m/s*
5.45
0.5864
Average
3.02 s
0.2843 m/s
0.09596 m/s*
4.69
0.4549

CALCULATIONS:
Wood Surface:
v=d/t               a=v/t                   F=ma  Ff=Mmg
v=1m/4.76s    a=0.2105/4.76    F=Ff
v=0.2101m/s  a=0.04441m/s*   0.08717N=M5kg(9.81m/s*)
                                                  M=0.0018
 
Cement Surface:
v=0.2968 m/s
a=0.08992
0.2841N=M(5kg)(9.81 m/s*)
M=0.0058
 
Sandpaper Surface:
v=0.2843 m/s
a=0.09596 m/s*
0.4549=M(5kg)(9.81 m/s*)
M=0.0093
 
 
OBSERVATIONS:
- The coefficent of friction for the sandpaper was the largest and the coefficent of friction for the wood was the smallest.
- It was harder to pull the rubber- bottomed box across the sandpaper which is a rough surface. This resulted in a stronger force needed.
-It was hard to do this lab and get good results because the box had to be pulled at a constant velocity which is very hard to do.
 
DISCUSSION:
     The results of this lab reflect on the different surfaces that cars drive on. The sandpaper had the highest coeffient of friction which means that the friction between the rubber and the sandpaper was great causing more traction. This high coefficent of friction is good because the car is less likely to slide off the road. The cement had the next highest coefficent of friction which is expected because it has similar properties to pavement which highways are made with. The coefficent is less then the one with sandpaper but there is still enough friction to allow a car to drive safely on it. The coefficent of friction of the wood is a lot lower then the cement and sandpaper surfaces. This shows that there is not enough friction between rubber and some surfaces which would cause the tire to slip and as a result the car will go off the road. Since the coefficent of friction of the wood is so much smaller then that of the sandpaper and cement imagine how small the coefficent of friction between the rubber and ice would be! It wood be smaller then that of the wood because ice is more slippery then wood.
 
CONCLUSION: Since the coefficent of friction of the wood is so much smaller then the sandpaper and cement it shows why it is harder to drive on some surfaces then others. This lab also shows why sand is put on icy roads to increase the amount of friction between the two surfaces.
 
 
   

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