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Speed, Velocity, and Momentum

Speed, Velocity, and Momentum. What is Speed?. Speed describes how fast an object moves. Speed equals the distance traveled divided by the time it takes to travel that distance. S = d/t. Units. The SI unit for speed is meters/second or m/s.

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Speed, Velocity, and Momentum

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  1. Speed, Velocity, and Momentum

  2. What is Speed? • Speed describes how fast an object moves. • Speed equals the distance traveled divided by the time it takes to travel that distance. • S = d/t

  3. Units • The SI unit for speed is meters/second or m/s. • If S = d/t, then meters measures the distance and seconds measures the time. • Speed is sometimes measured in km/h.

  4. Is Velocity different from Speed? • Speed only determines how fast an object is moving. • Velocity determines how fast an object is moving, but also determines in which direction the object is moving. • Speed = 45 m/s • Velocity = 45 m/s north • Velocity is also measured in m/s.

  5. Practice • 1. Find the velocity in meters per second of a swimmer who swims exactly 110m toward the shore in 72 s. • 2. Find the velocity in meters per second of a baseball thrown 38 m from third base to first base in 1.7 s. • 3. Calculate the distance in meters a cyclist would travel in 5.00 hours at an average velocity of 12.0 km/h to the southwest. • 4. Calculate the time in seconds an Olympic skier would take to finish a 2.6 km race at an average velocity of 28 m/s downhill.

  6. Change in Velocity • Can a car maintain a constant speed but still be changing in velocity? Why or why not? • Because velocity determines speed and direction, the velocity can change even if the speed doesn’t. • A car traveling at a constant speed in a circle is continuously changing velocity because it is constantly changing directions.

  7. Momentum • What would be harder to stop- a train or a car, if they were both moving at the same speed? Why? • The momentum of an object depends upon its mass and its velocity.

  8. Equation • Momentum = mass x velocity • p = mv • The unit for momentum is kg * m/s. • This is because mass is found in kg and velocity is found m/s.

  9. Practice • 1. Calculate the momentum of the following objects: • A. a 75 kg speed skater moving forward at 16 m/s. • B. a 135 kg ostrich running north at 16.2 m/s. • C. a 5.0 kg baby on a train moving eastward at 72 m/s. • D. a 0.8 kg kitten running to the left at 6.5 m/s. • E. a 48.5 kg passenger on a train stopped on the tracks.

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