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Forces & Newton’s Laws

Forces & Newton’s Laws. Chapter 11 Notes. Forces. A force is a push or pull exerted on an object Forces tend to change the motion of an object A force has two components Magnitude (how much) Direction (which way). Mass vs Weight. Many confuse the difference between mass and weight

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Forces & Newton’s Laws

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  1. Forces & Newton’s Laws Chapter 11 Notes

  2. Forces • A force is a push or pull exerted on an object • Forces tend to change the motion of an object • A force has two components • Magnitude (how much) • Direction (which way)

  3. Mass vs Weight • Many confuse the difference between mass and weight • Mass = How much matter an object has • Measured typically in grams (or kg) • Weight = Gravitation pull on an object • Weight = mass * gravitational acceleration

  4. Mass vs Weight • Take an object of mass 100 kg • On earth the mass = 100 kg • On the moon the mass - 100 kg • In outer space the mass = 100 kg • Weight of same object • On Earth the weight = 980 N • On the moon the weight = 160 N • In outer space the weight = 0 N

  5. Unit of Forces • There are several units that can be used to measure force • Many of you are most familiar with the unit of pound (lb) • The metric unit for force (the one we will use) is the Newton (N)

  6. Unit of Force • What is a Newton? • It is a derived unit • It is an abbreviation for: (Kg * m ) / s2

  7. Net Force • Net forces are more important than individual forces • A net force of the sum total of all the individual forces acting on an object • Net force is written as: ∑F

  8. Net Force • If the net force is zero the forces are considered to be BALANCED • If the net force is NOT zero the forces are considered to be UNBALANCED

  9. Balanced vs Unbalanced • When forces are BALANCED the motion of an object will remain constant • When forces are UNBALANCED the motion of an object will change…….it will ACCELERATE

  10. Net Force • Example: • Find the net force if a 300 N force acts to the right and a 120 N force acts to the left

  11. Net Force • Example: • Find the net force if a 400 N force acts to the right, a 120 N force acts to the left, and a 75 N forces acts to the left

  12. Friction • Friction is a force that opposes motion • It occurs when two surfaces are in contact • It depends on: • The weight of the object • The type of surfaces • Friction always slows down an object

  13. Types of Friction • Static friction • Occurs when the surfaces in contact do NOT slide past one another • Kinetic friction • Occurs when the surfaces in contact slide past one another

  14. Kinetic Friction • Kinetic friction is often referred to as sliding friction • If a round object rolls over a flat surface it is often referred to as rolling friction

  15. Types of Friction • Static friction is always greater than kinetic/rolling friction • Rolling friction is typically less than sliding friction Static > Sliding > Rolling

  16. Drag • Any object that moves through a fluid (like air) experiences a frictional force called air resistance • Another term for air resistance is DRAG

  17. Friction • Can be harmful • Engine parts • Air resistance • Can be helpful • Warming your hands • Starting/Stopping/Turning • Brillo pads

  18. Newton’s Laws • Sir Isaac Newton (1643-1727) • Developed Laws of motion

  19. Newton’s Laws • Newton was a student on break when he started to form his thoughts on motion • He challenged the belief system in regard to motion that had been establish over 2000 years ago

  20. Newton’s Laws • He summarized his thoughts into three Laws of Motion • Law of Inertia • F = ma • Action/Reaction Pairs

  21. Newton’s 1st Law • An object at rest will stay at rest OR an object in motion will stay in motion UNLESS a NET force acts on the object

  22. Newton’s 1st Law • Often referred to as the Law of Inertia • What is Inertia? • property of matter • tendency of an object to resist changes in motion • more mass = more inertia

  23. Newton’s 2nd Law • A net force acting on an object will cause the object to change its motion - it will accelerate • The magnitude of the force and the mass of the object will both influence the acceleration

  24. Newton’s 2nd Law • Written as an equation ∑ F = m a

  25. Newton’s 3rd Law • For every force there is an EQUAL but OPPOSITE reaction force • Examples • Baseball - Bat • Bug - Windshield

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