1 / 11

Measuring Friction between two surfaces

Measuring Friction between two surfaces. Free Body Diagram . Weight. Brick. Normal Force. Friction. Pull Force. Reaction . Surface. Coefficient of friction = Pull Force/ Normal Force (weight). Since block remains on same horizontal plane, it gains no potential energy.

dora
Download Presentation

Measuring Friction between two surfaces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measuring Friction between two surfaces Free Body Diagram Weight Brick Normal Force Friction Pull Force Reaction Surface Coefficient of friction = Pull Force/ Normal Force (weight) Since block remains on same horizontal plane, it gains no potential energy. However there is work done to overcome friction. Work = Pull Force X distance.

  2. Measuring Friction between two surfaces Weight = 20 newtons = normal force Pull force for smooth board = 5 newtons Coefficient of friction = u = 5/20 = 0.25 AMA = 20/5 = 4 IMA = 1 Work in = pull force / distance moved Work out = weight X height moved = 0 Efficiency = work out/work in = 0 Efficiency = is meaningless because we did not lift the weight

  3. Pull Force Normal Force C = Hypotenuse B = Height Friction Force a Inclined Planes for High School & College StudentsValidation requires measurements of pull force, weight & distances Reaction Force a A = Horizontal Distance a = angle Weight Free Body Diagram Showing vectors for forces Friction Force and component of weight Uphill Pull Force = u X Weight X Cos a + Weight X Sin a u = Frictional Force/Normal Force = Frictional Force/ Weight, for a = 0 A= Horizontal distance, B = Height, C= Hypotenuse a = angle IMA = C/B = 1/ Sin a; AMA = Weight/Pull Force; efficiency = AMA/IMA Pull Force / Weight = u Cos a + Sin a; Reaction = Normal Force Downhill Release Force = u X Weight X Cos a – Weight X Sin a If Downhill Release Force = 0, then u = Tan a.

  4. Lever as a Simple Machine Free Body Diagram {Vertical Distance weight moved} d a b c Weight Fulcrum Force {Vertical Distance moved by applied force} IMA = a/b; AMA = Weight/ Applied Force, efficiency = AMA/IMA From Geometry, b/a = d/c because of similar triangles. Efficiency = work out/work in = W X d/Force X c = AMA / a/b = AMA/IMA

  5. Physics Curriculum for Simple MachinesCalculating IMA, AMA and efficiency Beam Beam Beam Brick Brick Brick Two pulley system IMA = 2 (theory) AMA and IMA to be measured Single pulley system to measure friction IMA = 1 Four pulley system IMA = 4 (theory) AMA and IMA to be measured IMA & AMA is to be determined by the students and may disagree with theory because of friction of pulleys. Efficiency = AMA/IMA

  6. Physics Curriculum for Simple MachinesCalculation of Tension w/o friction T=W/2 Beam Beam Beam T=W/4 T= W/4 T=W/4 T=W/2 T= W/2 T = W/2 Weight Weight Weight Pull tension = W Pull tension =W/2 Pull tension = W/4 IMA = 2 IMA =1 IMA = 4 Presence of friction increases pull tension

  7. Catapult as a Simple Machine Free Body Diagram IMA = a/b; Pull X a = Force X b; AMA = Force/Pull; eff = work out/work in = Force X b/Pull X a = AMA/IMA Energy transferred = ½ X m V 2 (to object in cup) ;potential energy of spring = ½ k x2 Eff = ½ mv2 / ½ k x2 Cup k = spring constant (to be measured) Pull k is in lbs/ft a m = mass of object in cup in slugs v = velocity in ft/sec x = displacement of spring in feet Fulcrum b Spring Force Base

  8. Catapult as a Simple Machine a =23 inches; b = 3 inches; a/b = 7.66 = IMA; Pull = 95 NEWTONS = 21.1 lbs; Force on Spring = 7.66 X 21.1 = 161.6 lbs, Displacement of spring = 2.0 inches = 0.166 feet K = spring constant = 161.6 lbs/0.166 feet = 973.5 lbs/foot AMA = Force on Spring/Pull Force = 161.6 lbs/21.1 lbs = 7.66 IMA = 7.66; efficiency = IMA/AMA = 100% Energy imparted to spring = ½ k x2 = 0.5 x 973.5 lbs/foot X 0.166 foot X 0.166 foot = 13.41 lbs-feet Energy imparted to ball = ½ m V2 = 0.5 X (0.25 newtons/4.5 newtons/lb X V2 32.2 ft/sec2 = 0.0008626 lb sec 2/feet; 13.4 1 lbs -feet = 0.0008626 lb. sec2 /foot X V2 V = 124 ft/sec

  9. Wedge as a Simple Machine

  10. Wedge as a Simple Machine Sum of all vertical forces = 0 Sum of horizontal forces = 0 Sum of all angular forces = 0 F1 = u N1 , N1 = P F2 = u N2 , N2 = W Cos a F3 = u N3 , N3 = W • F3 • N3 F1 N1 W N2 F2 F2 N2 Angle = a

  11. Wedge as a Simple Machine Push Force, P. has to overcome the weight, W, and two friction forces. Ignore F1. u = coefficient of friction, a= angle P = W Sin a + W u + W u Cos a P = W (Sin a + u + u Cos a) W = 20 newtons, a = 4.67 deg, u = 0.25 P = 20 (0.0814 + 0.25 + 0.25 X 0.996) P = 11.6 newtons; AMA = 20/11.6 =1.72 IMA = 13.75/1.125 = 12.2 efficiency = AMA/IMA = 1.72/12.2 = 14%

More Related