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Physics 2.2

Physics 2.2. Speed and Velocity, Distance and Displacement:. Speed is a scalar quantity. Velocity is a vector quantity. Distance is a scalar. Displacement is a vector. Solve:. A car begins to ride at 20 m/s north and finishes at 30 m/s north. What is the average velocity?

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Physics 2.2

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  1. Physics 2.2

  2. Speed and Velocity, Distance and Displacement: • Speed is a scalar quantity. • Velocity is a vector quantity. • Distance is a scalar. • Displacement is a vector.

  3. Solve: • A car begins to ride at 20 m/s north and finishes at 30 m/s north. What is the average velocity? • Average velocity= initial + final velocity 2

  4. Graphs you should know: • Distance vs Time • Slope = ? • Velocity vs Time • Slope = ? • Area = ?

  5. Distance vs Time

  6. Velocity vs Time

  7. Velocity vs Time • We can deduct interesting information from a velocity-time graph: The slope of the line is the acceleration, but the area under the line is the displacement! • Let's see how to determine the displacement an object undergoes during a given time:

  8. Free Fall: • Use the Kinematic equations for constant acceleration. • Use 0 m/s for initial and starting velocities, and g for acceleration (-9.81 m/s). • After 1 second of free fall, what is the velocity of an object in free fall? 2 seconds?

  9. Time, Distance, and Velocity of an Object in Free Fall:

  10. Statics: • Forces which act on objects • Combined concurrent forces are called the resultant force

  11. Question? • Two concurrent forces on and object have a maximum resultant of 45 newtons and a minimum resultant of 5 newtons. What is the magnitude of each of these forces? • Solution: find the resultants in the same and opposite directions. • (20 N and 25 N).

  12. Finding the Resultant Graphically: • Parallelogram method: • Draw a mirror image of the two force vectors opposite them. • Measure the resultant. • Triangle method: • Draw the second force vector from the head of the first. • Measure the resultant.

  13. Parellelogram

  14. Triangle-method

  15. Equilibrium • Static equilibrium: • An object at rest. • Dynamic equilibrium: • An object with the net forces acting on it are equal to zero. Ex/ an object in free fall that has reached terminal velocity.

  16. Free body diagram

  17. Sir Isaac Newton’s Three Laws: • An object in motion tends to stay in motion, unless acted upon by a force. • When a force acts on an object, it will accelerate in the direction of that force • When a force acts upon and object, that object will act with and equal and opposite force.

  18. More… • Law of Inertia. • F = ma • F12 = F21

  19. ??? • Which object has the most inertia? • A 0.1 kg baseball travelling 20 meters/second. • A 10 kg sled at rest. • A 5 kg bowling ball traveling 3 meters/ second.

  20. ??? • An 8 N force is applied to a 4 kg block on a frictionless table. What is the magnitude of the block’s acceleration? • F = ma • 2 m/s²

  21. ??? • Which unit is equivalent to a newton per kg? • m/s² • W/m • j·s • kg·m/s

  22. Projectile moving Horizontally: • When an object is thrown from a height, there is both a horizontal and vertical component. • Find time in the air with: dy = vit + ½at²

  23. ??? • A baseball is thrown horizontally at 25 m/s from a cliff 45 meters above the level ground. How far from the base of the cliff does the ball hit the ground? • dx = vxt • dy = vit + ½at²

  24. A Projectile fired at an Angle: • Set up two sets of data: • Horizontal component x; • Vertical component y; • Use the kinematic equations to solve for both the horizontal and vertical components.

  25. ??? • A ball is thrown in the air at a 30˚ angle from the horizontal at a speed of 100 m/s. Find: • Time in the air • Max height • range

  26. Circular Motion • Centripetal acceleration • a = v²/r • Centripetal force • F = mv²/r

  27. ??? • A 2.0 E3 kg car travels at a constant speed of 12 m/s around a circular curve of radius 30. meters. • What is the magnitude of the centripetal acceleration of the car as it goes around the curve? • What direction is the centripetal force directed?

  28. Newton’s Universal Law of Gravity • F = Gm1m2/r² • Weight = mg

  29. Friction • Static friction: object is not moving • Fs = Us x Fn • Kinetic friction: object is moving • Fk = Uk x Fn

  30. Impulse and momentum • Impulse is the change in momentum. • J = Ft = ∆p • Momentum is mass x velocity. • p = mv

  31. A Simple pendulum: • Does mass effect the period?

  32. More pendulum stuff:

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