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Question O’ The Day

Question O’ The Day. What is a force? Take 1 minute and 37 seconds and talk about it with the people sitting around you. Be AS SPECIFIC as possible. (Bonus points for using the words vector or scalar in your explanation). Writing Assignment O’ The Day. On your whiteboard

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Question O’ The Day

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  1. Question O’ The Day • What is a force? • Take 1 minute and 37 seconds and talk about it with the people sitting around you. Be AS SPECIFIC as possible. (Bonus points for using the words vector or scalar in your explanation).

  2. Writing Assignment O’ The Day • On your whiteboard • Write down absolutely anything you know (or think you know) about forces. • It doesn’t matter if you’re right or wrong I just want to know what you think.

  3. Force is… • A force is a push or a pull resulting from aninteraction between objects. • Since you can’t push or pull without doing so in a direction…force is a vector. • The unit for force is….ehh actually we’ll wait a couple of days for that one.

  4. Gravitational Force • The force between two objects that have mass. • ALL objects that have mass are gravitationally attracted to each other. • http://www.youtube.com/watch?v=KDp1tiUsZw8

  5. Applied Force • A push or pull by a person. • http://www.youtube.com/watch?v=1FqpDmUO0y0

  6. Normal Force • The supportive force when one thing rests on another thing. • Squishy force. • Pillow force.

  7. Frictional Force • The force that opposes motion when moving or still. • Different surfaces cause different amounts of frictional forces. • Friction causes heat.

  8. Air Resistance Force • The force that occurs when particles of air hit a moving object, making it harder to move. • http://www.youtube.com/watch?v=AYJ1YBL39lo

  9. Spring Force • The force applied to a stretched or compressed spring wanting to return to it’s regular position. • http://www.youtube.com/watch?v=zG22qQydPVQ

  10. Tension Force • A pulling force in a string, rope, chain, or other similar material. • Bridges have lots of tension forces.

  11. Word Sort • Gravitational Force • Frictional Force • Applied Force • Tension Force • Normal Force • Air Resistance Force • Spring Force

  12. Contact Forces • Applied • Air Resistance • Frictional • Normal (Pillow force) • Spring • Tension

  13. Action at a Distance Forces • Gravitational • Electric • Magnetic

  14. Research!

  15. Forces Examples

  16. Hover Disc Demos

  17. Free Body Diagrams • Free body diagrams are used to represent the forces acting on any given object. • Let’s do some (actually…a whole bunch of) practice problems. • Come on up and grab whiteboards. • On one whiteboard sketch out the system schema. • On another whiteboard sketch out the Free Body Diagram

  18. Free Body Diagrams • A book is at rest on a tabletop. Diagram the forces acting on the book.

  19. Free Body Diagrams • A person is suspended motionless from the ceiling by two ropes. Diagram the forces acting on the person.

  20. Free Body Diagrams • An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it is falling.

  21. Free Body Diagrams • A flying squirrel is falling vertically from a tree to the ground at constant velocity. Consider air resistance. Diagram the forces acting on the squirrel.

  22. Free Body Diagrams • A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book.

  23. Free Body Diagrams • A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book.

  24. Free Body Diagrams • A college student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder. Diagram the vertical forces acting on the backpack.

  25. Free Body Diagrams • A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.

  26. Free Body Diagrams • A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration. Diagram the forces acting upon the sled.

  27. Free Body Diagrams • A football is moving upwards towards its peak after having been booted by the punter. Diagram the forces acting upon the football as it rises upward towards its peak. Neglect air resistance.

  28. Free Body Diagrams • A car is coasting to the right and slowing down. Diagram the forces acting upon the car. Neglect air resistance.

  29. Elevator Activity: 1.24.14 • Elevator Activity • http://www.youtube.com/watch?v=8BODmDUdh-c • Big Ideas: • Unbalanced forces cause acceleration (speed up or slow down). • Balanced forces mean things are moving with a steady velocity.

  30. Things About Stuff • Stuff is lazy. • Stuff likes to do whatever it’s doing unless something makes it do something different.

  31. Law of Laziness • Mr. Heffernan’s Law of Laziness- • If something is not moving it will keep not moving unless something makes it move. • If something is moving it will keep moving in the same way unless something makes it change how its moving.

  32. Newton’s First Law • Newton’s 1st Law- • An object moves with a constant velocity unless a force causes it to accelerate.

  33. Inertia • Inertia- The resistance of an object to a change in it’s motion. • Inertia = Laziness • The inertia of an object is directly proportional to its mass. • Mo’ Mass, Mo’ Inertia

  34. Question

  35. Question

  36. Inertia • How would playing with the hover disc be different if it was more massive?

  37. Answer Questions

  38. Gravitational Force

  39. Mass vs. Weight • Mass – Mass never changes • How much stuff is present in something. • Weight = Gravity Force= Fgrav • How much that stuff is pulled toward another object due to gravity.

  40. Gravity Force a minute… • In our lab we saw that there is a relationship between the mass of an object and the gravitational force on that object • Weight = Gravity * Mass • Newtons = m/s2 * kg

  41. Sample Problem

  42. Stop • Answer Questions

  43. The following box is sitting on a table located on Earth. Determine the missing forces. 12kg

  44. The normal force is “smart”.

  45. Question • A 5 kg wooden box is being pushed to the right along a wooden table with a constant velocity of 4 m/s. What’s the normal force acting on the box? (Always start with a Free Body Diagram)

  46. STOP

  47. Question O’ The Day • My Goal in Life. • Friction Lab

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