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Force in a Mechanical System

UNIT 2. Force in a Mechanical System. What is Principles of Technology?. Broken into many units that each have 4 subunits based on the 4 energy systems. 4 basic energy systems. Mechanical Fluid Electrical Thermal. Principles of Technology. Push or pull How force is applied

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Force in a Mechanical System

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  1. UNIT 2 Force in a Mechanical System

  2. What is Principles of Technology? • Broken into many units that each have 4 subunits based on the 4 energy systems

  3. 4 basic energy systems • Mechanical • Fluid • Electrical • Thermal

  4. Principles of Technology • Push or pull • How force is applied • How fast or slowly something moves • Opposition to force • Force – Term 1 • Work – Term 2 • Rate – Term 3 • Resistance – Term 4

  5. Unit 2 Force Pages 9-17 • Pound • Newton • Unbalanced • Balanced • Net Force • Equilibrium • Magnitude • Direction • Vector • Scalars • Arrow length • Arrow heading • Weight • Gravity • Mass • Torque

  6. Section Review Page 20-21 #1-11

  7. What is Force? • Force is a push or pull • Lifting, walking, breathing • Arm wrestling, cranes, earth movers

  8. What can a force do? • Cause an object to start moving or to move faster • Cause a moving object to change direction • Cause an object to slow down or stop • Change the shape of an object

  9. Force is the prime mover in the mechanical system What are the others primemovers?

  10. Energy System Prime Movers • Force • Pressure • Voltage • Temperature Difference Mechanical Fluid Electrical Thermal

  11. Why do we need to know this? • Few of technicians are narrow specialists • The need for “many-skilled” technicians is on high demand and growing

  12. Balancing Forces • The English unit for force is pound (lb) • SI unit is Newton (N) • Balanced vs. Unbalanced forces • Fence/Wall vs. Lawnmower

  13. Unbalanced • Weight > Drag

  14. Balanced • Drag = Weight

  15. Net Force • If there are unbalanced forces then there is said to be a net force • This will cause a change in the objects speed, direction, and perhaps shape

  16. Equilibrium • When all forces acting on a body are equally balanced and cancel each other out • Walls of a house, bridge

  17. Describing forces • Forces are always given a magnitude and direction • This is a “vector” • Magnitude only = scalars

  18. Describing forces • Arrow length = magnitude • Arrow heading = direction

  19. Describing forces

  20. Describing forces

  21. Adding Forces • When forces are in the same direction we add them • When they are opposite we subtract them

  22. Combining Forces 50lb 50lb 50lb - 35lb 35lb 35lb 150 lb total - 105 lb Net Force = 45 lb

  23. Describing forces

  24. Describing forces

  25. When measuring angles... 90 205o 45o 0 180 25o 270

  26. Combining Forces at Angles How do we combine the forces? 30 lb Dock What do you think the net force will be? In what direction? 40 lb

  27. Dock

  28. Then use a ruler and protractor to find the vector AC

  29. Then use the Pythagorean theorem A2 +b2 = c2

  30. Use Soh Cah Toa to find the angle

  31. Dock Find the magnitude and direction of the resultant force

  32. When measuring angles... 90 104o 76o 180 0 270

  33. With the Pythagorean theorem

  34. Final Answer: 62 lbs @ 104 degrees

  35. Find the magnitude and direction of the resultant force 20 lbs 70 lbs

  36. Find the magnitude and direction of the resultant force 20 lbs 70 lbs

  37. Weight vs. Mass • Are they the same thing? NO !

  38. Mass • Total amount of matter contained in an object • Depends on the type and number of atoms contained in an object • English – pound mass (lbm) • (Or slug = 32.2lbs) • SI – kilogram (kg)

  39. Weight • Measure of the (Earths) gravitational pull • English – Pounds (lb) • SI – Newtons (N) • Weight on moon = 1/6 on Earth

  40. English & SI Units

  41. Weight & Mass Conversions • 1 pound = 16 ounces • 1 pound = 4.45 Newtons (weight) • 1 kilogram = 1000 grams • 1 pound mass (lbm) weighs 1 pound • 1 kilogram mass weighs 9.8N or 2.2 lb

  42. Weight & Mass Conversions • What is the weight of a 35000g mass in Newtons? CPS 1

  43. Weight & Mass Conversions • What is the weight of a 35000g mass in Newtons? • 35000g = 35kg • 1kg weighs 9.8N • 35kg = 343N

  44. Weight & Mass Conversions • What is the weight of a 35000g mass in Newtons? • How many pounds is that on Earth? CPS 2

  45. Weight & Mass Conversions • How many pounds is that on Earth? • 35000g = 35kg • 1kg = 2.2lbs • 35kg = 77lbs

  46. Weight & Mass Conversions • What is the weight of a 35000g mass in Newtons? • How many pounds is that on Earth? • What is its mass on the moon? CPS 3

  47. Weight & Mass Conversions • What is its mass on the moon? Mass doesn't change when you go to the moon!!!

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