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Speed, Velocity, and Momentum

Learn the differences between speed and velocity, how to calculate velocity, and the concept of momentum in physics with examples and practice exercises.

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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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