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Warm Up – 1/6/11

Warm Up – 1/6/11. If you are sitting still in a seat on a moving bus that is traveling on the highway, is your body at rest or in motion? Explain your answer. Newton’s Laws.

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Warm Up – 1/6/11

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  1. Warm Up – 1/6/11 • If you are sitting still in a seat on a moving bus that is traveling on the highway, is your body at rest or in motion? Explain your answer.

  2. Newton’s Laws Isaac Newton developed the three laws that describe all the states of motion - rest, constant motion, and accelerated motion. These three laws explain how forces cause all the states of motion.

  3. Newton’s First Law • An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted upon by an unbalanced force.

  4. Part 1 • An object at rest • An object at rest will not move until a push or a pull is exerted on it. • Ex. You must pull on a chair to get it to move out from under a table.

  5. Inertia • The property of an object that resists changes in its state of rest or motion. When stationary difficult to push. When moving difficult to stop.

  6. Inertia depends on mass. Which would have more inertia? A child on a swing or an adult on a swing?

  7. Part 2 • An object in motion • In order to slow, speed up or change the direction of an object an unbalanced force must act upon it.

  8. · Sudden Starts - head rests stop the head from being pushed back. (rapid positive acceleration) · Sudden Stops - seat belts help your body resist the tendency to keep moving. (rapid negative acceleration)

  9. Newton’s Second Law • The acceleration of an object depends on the mass of the object and the amount of force applied. • F = m x a

  10. Part 1 • Acceleration Depends on Mass • More force is needed to accelerate objects that have more mass. • If the same force is applied to an object with a large mass vs. a small mass the smaller object will go farther because it is easier to accelerate.

  11. Part 2 • Acceleration Depends on Force • If you put more force on the same size object it will move faster. • An objects acceleration increases as the force on the object increases. • F = m x a

  12. Newton’s Third Law • Whenever one object exerts a force on another object, the second object exerts and equal and opposite force on the first. • All forces act in pairs. • When a force is exerted and equal and opposite force occurs (sitting in a chair). • Without action/reaction forces there would be no motion. • These 2 forces act on different objects.

  13. Action-reaction force pairs make it possible for fish (or humans) to swim. • A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite to the direction of the force on the fish (forwards).

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