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Forces of Friction Lab
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| Frictional Forces Lab Lab Group Members: Ivy Armstrong, Brianna Mack and Brittany Penner November 2, 2002 Purpose: To explore the forces of friction by testing the forces needed to get a mass moving and the forces that are needed to keep the mass at a constant velocity. We will test these forces by doing several trials of dragging a wooden sleigh along a wooden ramp. Unfortunately because of the short length of the wooden plank and inaccurate measuring equipment, the results will be inaccurate and in a science land we would have better luck at accurate results. Procedure: 1. Gather all of your materials, including a board, wooden sleigh, Newton scale, metal plate/weight, meter stick and a scale. 2. Take the mass of your wooden sleigh and all of the weights you will be using. 3. Measure the length of the board and prop it up against some sort of solid object, measuring the height so you can, at a later time, find the angle from the horizontal. 4. Measure the force being applied on your wooden sleight in N, then measure the force on your wooden sleight with the various weights. 5. Attach you sleight to your scale and lay the sleigh on the board, holding it stationary and then gently pulling on the Newton scale until the sleigh begins to move. Write down the force needed to move the sleigh from the stationary position. 6. Repeat step 5 for at least one other height, and with at least one weight attached at all heights. 7. Attach your wooden sleigh to your Newton Scale and lay the sleight at the bottom of the board. Pull the sleigh with a constant velocity up the board, writing down the force applied. 8. Repeat step 7 for at least one other height, and with at least one weight attached at all heights. 9. To do the data analysis you must figure out the Fn, and Ff by doing the calculations as illustrated below. 10. These values can be used in the friction equation to find the constant values of slope. 11. These slope values are used to compare forces of friction in constant velocity and static friction situations. Data: Constant Velocity Sleigh Mass (g) / (kg) 292.8 0.2928 Extra Mass (g) / (kg) 749.3 0.7493 Sleigh Weight (N) 2.8 Calibrated Acceleration (m/s^2) 9.6 trial 1 trial 2 trial 3 trial 4 trial 5 trial 6 Fp (force of pull) 1 (N) 1.4 5.0 0.6 2.7 1.5 3.7 Fp 2 (N) 1.5 5.0 0.7 2.8 1.5 4.0 Fp 3 (N) 1.5 5.0 0.6 3.0 1.3 3.8 Fp 4 (N) 1.4 4.9 0.7 3.2 1.4 3.7 Fp 5 (N) 1.4 5.1 0.8 2.9 1.6 3.9 Length of ramp (cm) 235.6 235.6 243.6 243.6 243.6 243.6 Height of ramp (cm) 75.0 75.0 26.0 26.0 55.0 55.0 Angle of ramp (degrees) 18.6 18.6 6.1 6.1 13.0 13.0 Mass 0.2928 1.0421 0.2928 1.0421 0.2928 1.0421 STATIC Calibrated Acceleration (m/s^2) 9.6 trial 1 trial 2 trial 3 trial 4 Fp 1 (N) 1.1 5.8 0.5 3.0 Fp 2 (N) 1.2 5.5 0.6 3.0 Fp 3 (N) 1.0 5.8 0.6 3.0 Fp 4 (N) 1.1 5.2 0.6 3.1 Fp 5 (N) 1.3 5.5 0.6 3.1 5.5 0.6 3.0 5.2 3.1 5.2 5.2 5.2 Length of ramp (cm) 235.6 235.6 243.6 243.6 Height of ramp (cm) 75.0 75.0 26.0 26.0 Angle of ramp (degrees) 18.6 18.6 6.1 6.1 Mass 0.2928 1.0421 0.2928 1.0421 Questions: 1. Another variation on this experiment would be to evaluate the coefficients of frictions for materials which are not the same. This can be accomplished simply by taking two different surfaces and rubbing one on to the other at a constant velocity. Then you can calculate the coefficient of friction by using the angle of the stationary surface to the ground. This coefficient would be only accurate for the similar situation. 2. The coefficient of friction between the rubberized floor and the wood would be much less because the rubberized floor has less particlized*, bumpy surface as compared to the very particlized*, bumpy surface of the sandpaper. The more particlized* the surfaces the more friction which is formed between the two surfaces. 3. The force of friction is influenced by two main factors. First, the angle of the one surface to the ground influences the friction because the greater the angle the less the more the friction. This is because with a great angle there is less of a downward, gravitational force and more of a frictional force. The other factor that influences the force of friction greatly is how particlized* the surfaces are. The bumpier the surface on the molecular level the more force of friction that is present. 4. All four of the recognized forces influence the force of friction. The gravitational force creates a “towards the center of the earth” pull creating contact between materials. This contact is the reason for the force of friction. The electromagnetic forces have photons which create friction within each other. Weak nuclear force holds molecular bonds together and thus it is the reason for particlized* surfaces on the molecular level. These particlized* surfaces are the cause of friction. The strong nuclear force is needed in the friction occurrence because without the proton-neutron force the weak nuclear force would not be able to occur. Sample Calculations: Calculating the angle of the ramp. Sin = height of the ramp Length of the ramp Sin =(75.0 cm)/(235.6 cm) Angle of ramp= 18.6 degrees Finding the Fn. First you take your gravitational pull in N And split it into a triangle so that you have a side that is parallel to ramp. The angle that is formed by the floor and the ramp is equivalent to angle of the downward force and the force that is opposite of the Fn. Cos(ramp angle) = adjacent Hypotenuse Cos18.6 = x/2.8 X= 2.65 N To find the value simply look at the slope of the graph. Table of Results: The colour section are what is included on the graphs. Constant Velocity trial 1 trial 2 trial 3 trial 4 trial 5 trial 6 Force of friction Ff 1 (N) 0.51 1.83 0.30 1.64 0.87 1.45 Force of friction Ff 2 (N) 0.61 1.83 0.40 1.74 0.87 1.75 Force of friction Ff 3 (N) 0.61 1.83 0.30 1.94 0.67 1.55 Force of friction Ff 4 (N) 0.51 1.73 0.40 2.14 0.77 1.45 Force of friction Ff 5 (N) 0.51 1.93 0.50 1.84 0.97 1.65 Average force of kinetic friction Fk (N) 0.55 1.83 0.38 1.86 0.83 1.57 Normal Force Fn (N) 2.65 9.45 2.78 9.91 2.73 9.71 Coefficient of kinetic friction 0.1669 Static trial 1 trial 2 trial 3 trial 4 Force of friction Ff 1 (N) 0.21 2.63 0.20 1.94 Force of friction Ff 2 (N) 0.31 2.33 0.30 1.94 Force of friction Ff 3 (N) 0.11 2.63 0.30 1.94 Force of friction Ff 4 (N) 0.21 2.03 0.30 2.04 Force of friction Ff 5 (N) 0.41 2.33 0.30 2.04 Force of friction Ff 6 (N) 2.33 0.30 1.94 Force of friction Ff 7 (N) 2.03 2.04 Force of friction Ff 8 (N) 2.03 Force of friction Ff 9 (N) 2.03 Force of friction Ff 10 (N) 2.03 Average force of static friction fs (N) 0.25 2.24 0.28 1.98 Normal Force Fn (N) 2.65 9.45 2.78 9.91 Sources of Error: 1. The Newton scale started at a location other than 0. There also was a spot where the needle tended to stick. Although, we still achieved consistence answers and our graphs where basically straight lines. The problem can be solved by calibrating the scales correctly or purchasing higher quality equipment. 2. The balance scale was not properly calibrated therefore gravity by its standards was 9.6 m/s2 [down]. Although, again our data was consistent, we did have to use 9.6 m/s2 [down] as our gravitational pull for our calculations. The problem can be solved by calibrating the scales correctly or purchasing higher quality equipment. 3. Splitters and particles that fall off the sleigh and ramp during the duration of our experiment cause the equipment to be ever changing and thus giving us a variance in the results. It is not a huge problem because these microscopic changes would not be apparent on the inaccurate measuring devices. This problem is not easily solved because this happens for all types of materials except our fun frictionless equipment in physics land. Conclusion: In conclusion, we found that the coefficient of friction for a constant velocity is 0.1669 And, the coefficient for static friction is 0.2629 We found that the coefficient values for static friction are greater than for the equivalent situation in constant velocity friction. The variance of the points on our graph is due to the sources of error outlined above. The direct proportional relationship between the Ff and the Fn was proven in our lab. We know that this relationship exists because our graphs proved it. This lab was moderately accurate and could only be improved by using more scientifically accurate measuring devices. Further, it would be nice to explore the forces of friction in occurrences when the materials are not the same. *Particlized: is an abudance of particles along the surface of a material |