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Chapter 11: Forces

Chapter 11: Forces. Already Covered: Newton’s 1 st and 2 nd laws of motion: An object at rest remains at rest , and an object in motion remains in motion with the same velocity , unless acted upon by an unbalanced force

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Chapter 11: Forces

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  1. Chapter 11: Forces Already Covered: Newton’s 1st and 2nd laws of motion: An object at rest remains at rest, and an object in motion remains in motion with the same velocity, unless acted upon by an unbalanced force The acceleration of an object increases with increased force and decreases with increased mass F = m x a 2.3 Forces act in pairs Netwon’s 3rd Law: 3. Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object

  2. Newton’s third law relates action and reaction forces • Forces always act in pairs • Jellyfish movement: squeeze water out of the umbrella-like body: applies a force (of the water) in one direction (downward), and moves in the opposite direction (upward) • “Every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object” • (For every action there is an equal and opposite reaction.)

  3. Action and Reaction Pairs • Force exerted on an object/force the object exerts back = action/reaction force pair • Jellyfish? • Book’s ex: • Space shuttle launch • Stub your toe • Press down on a table (no motion)

  4. Action and Reaction Forces Versus Balanced Forces • Equal AND opposite, similar to balanced forces • Balanced forces act on a single object: two friends pulling on a back pack, which doesn’t move • Action and Reaction Forces act on different objects: drag the back pack across the floor • Examples?

  5. The baseball forces the bat to the left; the bat forces the ball to the right. Together, these two forces exerted upon two different objects form the action-reaction force pair. Note that in the description of the two forces, the nouns in the sentence describing the forces simply switch places. Action: Baseball pushes glove leftwards. Reaction: _________________________ Action: Bowling ball pushes pin leftwards. Reaction: _________________________ Action: Enclosed air particles push balloon wall outwards. Reaction: _________________________

  6. Newton’s three laws describe and predict motion • Can explain the motion of almost any object (animals included) • Work together (not independent of one another) • Can use the laws to make predictions about motion • Spacecraft: can predict where Mars will be at the time a spacecraft reaches it, and can control the force on the spacecraft to arrive at the right place/time

  7. Newton’s three laws of motion Acceleration is Independent of Mass Inertia Trick

  8. Inertia is Mass Three Examples of Inertia

  9. Newton's Laws of Motion Newton's First Law

  10. Newton's Second Law:  Acceleration = Force / mass Adding and Subtracting Forces

  11. Equilibrium Means "Zero Acceleration" Equilibrium

  12. Acceleration Due to Gravity

  13. Weight

  14. Terminal Speed

  15. Newton's Third Law of Motion:  Action-Reaction 

  16. More Action-Reaction Pair Examples

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