friction l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Friction PowerPoint Presentation
Download Presentation
Friction

Loading in 2 Seconds...

play fullscreen
1 / 16

Friction - PowerPoint PPT Presentation


  • 241 Views
  • Uploaded on

Friction. Friction in machines wastes energy Wastes energy and can be transferred into heat. Advantages: Starts/stops machines Wet or icy roads Sand or gravel. Three Factors Determine Friction. Primary Cause: minute irregularities in rubbing surfaces Force pressing two surfaces together.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Friction' - red


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
friction
Friction
  • Friction in machines wastes energy
  • Wastes energy and can be transferred into heat.
  • Advantages: Starts/stops machines
    • Wet or icy roads
    • Sand or gravel
three factors determine friction
Three Factors Determine Friction

Primary Cause: minute irregularities in rubbing surfaces

  • Force pressing two surfaces together.
  • Nature of substances in contact with each other- Coefficient of friction
  • Kind of motion involved
static friction
Static Friction
  • Inertia that has to be overcome to start object moving
  • Condition of surface plays big role in how much starting friction is
    • “Coefficient of Friction” has been established for various materials
    • Typically found in table form
static friction4
Static Friction
  • Equation:
  • Ex: 60# block, k=0.3 static force is parallel to friction
  • What is the static force?
static force more examples
Static Force – more examples
  • Force due to weight parallel to friction
  • Holding something in a vise
  • Static force perpendicular to wt and friction
  • Equation:
  • 12 lb block supported in vise, k=0.18
  • Force exerted on each face of block?
sliding friction
Sliding Friction
  • Force needed to keep an object moving on surface
  • Amount of sliding resistance dependent upon nature of surface and normal force (weight) between the object and surface
  • Equation:
sliding friction7
Sliding Friction
  • Put a wedge under a block
  • u=0.09, block = 100#, wedge 12 ft long and 2 ft high
  • Break it down into two parts
    • Force to put block on wedge
    • Force sliding block
rolling friction
Rolling Friction
  • Rolling friction greatly reduced because of the action of roller and bearings
  • Coefficient usually low:
    • Tire on concrete: u=0.02
    • Roller bearing: u=0.001 – 0.003
  • Equation:
rolling friction example
Rolling Friction Example
  • Wheelbarrow = 500#, tire: u = 0.02

F = 500 x 0.02 = 10#

power
Power
  • NOT ability to move large objects
  • Power is the rate of doing work
  • Digging a trench: 1 man = 60days; 2 men = 30 days, 1 backhoe = 1 day
  • Same work, different power
power example
Power example
  • Engine = 3500# hoisted vertically 7 ft in 3 mins. Calculate the power.
  • What if 1 min?
horsepower
Horsepower
  • Power is often expressed in “horsepower”
  • Equation:
  • Equation:
work equivalents btus
Work Equivalents: BTUs
  • Heat energy can be transformed to mechanical energy
  • Mechanical energy can be converted to heat energy
    • Pilot slows airplane after touchdown, applying brakes. Kinetic energy of moving aircraft changes to heat energy – hot disks & hot tires
work btu conversion
Work – BTU Conversion
  • 1 BTU = 778 ft-lbs of work
  • Example: 1500# weight lifted vertically 300 ft in 45 minutes
  • Work done lifting the weight?
  • How many BTU’s?
  • Power?
same example continued
Same example, continued
  • Horsepower?
  • Now rework with t = 45 sec.
  • 45 sec = 0.75 hr
another example
Another Example
  • What if we had a 350# aircraft engine 2.5 ft above the engine mount on a hoist, and we move the hoist horizontally 15 ft in 15 sec.
  • How much work was accomplished?
  • How much Power?
  • How much Horsepower?
  • How many BTU’s?