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Chapter 18

Chapter 18. Motion and Momentum. Matter and Motion. All matter in the universe is in constant motion When an object moves from one location to another, it changes position Point of Reference Determines a change in position. Distance and Displacement. Distance

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Chapter 18

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  1. Chapter 18 Motion and Momentum

  2. Matter and Motion • All matter in the universe is in constant motion • When an object moves from one location to another, it changes position • Point of Reference • Determines a change in position

  3. Distance and Displacement • Distance • The length of the route traveled • Displacement • The direction and the difference in position between your starting and ending points

  4. Speed • The distance traveled divided by the time taken to travel the distance • Speed (meters/second)= distance/time • S=d/t • Calculate the speed of a swimmer who swims 100 m in 56 seconds.

  5. Average Speed vs. Instantaneous Speed • Average Speed • Found by dividing the total distance traveled by the time taken • Instantaneous Speed • The speed of an object at one instance of time

  6. Graphing Motion • Time is plotted on the horizontal axis • Distance is plotted on the vertical axis

  7. Velocity • The speed of the object and the direction of its motion • May change if the object’s speed, velocity, or both changes.

  8. Acceleration • The change in velocity divided by the time it takes for the change to occur • Has direction • Speeding Up • Direction that the object is moving • Slowing Down • Opposite to the direction that the object is moving • Angle • Turns toward direction of acceleration

  9. Acceleration Equation • Acceleration (m/s2)= • (final speed (in m/s) - initial speed (in m/s)) / time (in s) • a= (sf – si) / t • Calculate the acceleration of a bus whose speed changes from 6 m/s to 12 m/s over a period of 3 s.

  10. Positive and Negative Acceleration • Both positive and negative acceleration may be calculated with the previous equation. • If the acceleration is positive, add a + sign to the beginning of your answer. • If the acceleration is negative, add a – sign to the beginning of your answer.

  11. Graphing Acceleration • Speed or velocity is on the vertical axis • Time is on the horizontal axis

  12. Mass and Inertia • Mass • Amount of matter in an object • The more mass an object has, the harder it is to start moving, and the harder it is to slow it down. • Inertia • An object’s tendency to resist a change in its motion • The more mass an object has, the harder it is to change its motion

  13. Momentum • A measure of how hard it is to stop an object in motion • Momentum (in kg * m/s) = mass (in kg) x velocity (in m/s) p= mv • Calculate the momentum of a 14 kg bicycle traveling north at 2 m/s.

  14. Law of conservation of momentum • The total momentum of objects that collide is the same before and after the collision

  15. Chapter 19 Force and Newton’s Laws

  16. Force • A push or a pull • An object will speed up, slow down, or turn only if something is pushing or pulling it • Many different kinds of forces: • Magnetic, gravitational, Intentional

  17. Net Force • The combination of all the forces acting on an object • Determines the motion on an object • Object at rest has a net force of zero • Same direction=add together • Opposite direction=difference between two

  18. Balanced vs. Unbalanced Forces • Balanced Forces • When 2 or more forces exerted on each other are equal and cancel each other out • Do not cause a change in motion • Net force is zero • Unbalanced Forces • Forces do not cancel each other out • Net force is not zero • Motion of object changes

  19. Newton’s First Law of Motion • If the net force acting on an object is zero, the object remains at rest, or if the object is already moving, continues to move in a straight line with constant speed.

  20. Friction • The force that acts to resist sliding between two touching surfaces • The force that brings nearly everything to a stop • First proposed by Galileo • Motion of an object doesn’t change until an unbalanced force acts on it

  21. Newton’s Second Law of Motion • An object acted upon by a force will accelerate in the direction of the force • Acceleration (meters/second2) = net force (in newtons) / mass (in kilograms) • a = Fnet / m or Fnet = ma

  22. Gravity • Force that exists between an object and Earth • Always attractive and pulls objects toward each other • Responsible for pulling us downward and for Earth’s orbit the Sun, as well as Moon’s orbit around Earth

  23. Weight • The measure of gravitational pull on an object • Causes all objects to fall at an acceleration of 9.8 m/s2 • Mass never changes, but weight changes depending on location (example.. space)

  24. Newton’s Third Law of Motion • Forces always act in equal but opposite pairs • For every action, there is an equal but opposite reaction • Action/Reaction forces don’t cancel because they act on different objects.

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