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Understanding Motion: Speed, Velocity & Acceleration in Physics

Dive into the world of motion with this comprehensive guide covering concepts like speed, velocity, acceleration, momentum, and more. Learn how to calculate speed, differentiate between speed and velocity, grasp the significance of frames of reference, and explore the principles of momentum in physics.

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Understanding Motion: Speed, Velocity & Acceleration in Physics

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  1. Chapter 12What is Motion? Describing Motion Frame of Reference Motion Speed & Velocity Acceleration Momentum

  2. Motion • Problem: • Is your desk moving? • We need a frame (point) of reference... • a nonmoving point from which motion is measured

  3. Reference point Motion Motion • Motion • Change in position in relation to a point of reference.

  4. Motion Problem: • You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. • You have mistakenly set yourself as the reference point.

  5. d s t Speed • Speed • rate at which an object moves • distance traveled per unit time

  6. Speed • Instantaneous Speed • speed at a given instant • ex - the car is going 35 mph right now • Average Speed • The average speed of the entire journey

  7. Velocity • Problem: • A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried? • It depends on the storm’s direction!

  8. Velocity • Velocity • speed in a given direction • Velocity can change even when the speed is constant!

  9. d t v Calculations of Speed & Velocity • Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster? GIVEN: d = 100 m t = 20 s s = ? WORK: s = d ÷ t s = (100 m) ÷ (20 s) s = 5 m/s You skate faster!

  10. d t v Calculations of Speed & Velocity • Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it? GIVEN: v = 330 m/s d = 1km = 1000m t = ? WORK: t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s

  11. Distance-Time Graph A B Graphing Speed & Velocity • distance vs. time graph • the slope is = to • speed • steeper slope means • faster speed • straight line means • constant speed • flat line means • no motion

  12. Distance-Time Graph A B Graphing Speed & Velocity • Who started out faster? • A (steeper slope) • Who had a constant speed? • A • Describe B from 10-20 min. • B stopped moving • Find their average speeds. • A = (2400m) ÷ (30min) A = 80 m/min • B = (1200m) ÷ (30min) B = 40 m/min

  13. Distance-Time Graph Graphing Speed & Velocity • Acceleration is indicated by a curve on a Distance-Time graph. • Changing slope = changing velocity

  14. vf - vi t a Acceleration • Acceleration • the rate of change of velocity • change in speed or direction a: acceleration vf: final velocity vi: initial velocity t: time

  15. Acceleration • Positive acceleration • “speeding up” • Negative acceleration • “slowing down”

  16. vf - vi t a Acceleration Calculations • A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? GIVEN: vi = 10 m/s t = 3 s vf = 32 m/s a = ? WORK: a = (vf- vi) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a= 7.3 m/s2

  17. vf - vi t a Acceleration Calculations • How long will it take a car traveling 30 m/s to come to a stop if its acceleration is - 3 m/s2? GIVEN: t = ? vi = 30 m/s vf = 0 m/s a = -3 m/s2 WORK: t = (vf- vi) ÷ a t = (0m/s-30m/s)÷(-3m/s2) t = -30 m/s ÷ -3m/s2 t = 10 s

  18. Speed-Time Graph Graphing Acceleration • slope = • straight line = • flat line = acceleration • +vel = speeds up • -vel = slows down constant accel. no accel.(constant velocity)

  19. Speed-Time Graph Graphing Acceleration Specify the time period when the object was... • slowing down • 5 to 10 seconds • speeding up • 0 to 3 seconds • moving at a constant speed • 3 to 5 seconds • not moving • 0 & 10 seconds

  20. momentum = mass • velocity Momentum • All moving objects have momentum • Momentum depends on the mass of the object and the velocity with which it is traveling p • Formula for calculating momentum v m

  21. Conservation of Momentum • The total momentum of any group of objects remains the same unless outside forces act on the objects. • Ex. 2 billiard balls hit into one another. • The total momentum of the 2 balls before they collide is the same as the total momentum of the two balls after they collide.

  22. Momentum Calculations • What is the momentum of a 0.3 kg bluejay flying at 17 m/sec? GIVEN: p = ? v = 17 m/s m = 0.3 kg WORK: p = m • v p = 0.3 kg •17 m/s p = 5.1 kg•m/sec p v m

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