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Intro to Motion

Intro to Motion. Uniform and Non-Uniform Motion Speed and Velocity. Framing Questions. What is the difference between uniform motion and non-uniform motion? What are examples of each? What is the difference between speed and velocity? What are the formulas for speed and velocity?.

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Intro to Motion

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  1. Intro to Motion Uniform and Non-Uniform Motion Speed and Velocity

  2. Framing Questions • What is the difference between uniform motion and non-uniform motion? • What are examples of each? • What is the difference between speed and velocity? • What are the formulas for speed and velocity?

  3. Uniform vs. Non-Uniform Motion • Uniform or constant motion is movement in a straight line at a constant speed • Ex: A cyclist traveling on a straight path at a speed of 10m/s. • Uniform motion rarely exists… how many times do you see something going at precisely the same speed in a precisely straight line? • This is what we will explore this week: constant velocity • Any movement not in a straight line or not at a constant speed is called non-uniform motion • Ex: A car traveling around a corner • Most enduring motions are non-uniform • This is what we will explore next week: changing velocity, or acceleration.

  4. Exercise: Uniform or Non-Uniform? • A steel ball is dropped from your raised hand to the floor • A car is traveling north at a constant speed for 2 hours • A jogger is running around a circular track at a constant speed • A car is traveling a steady 60km/h due west • A leaf flutters to the ground • A rocket is launched from the Earth towards the moon • A motorcycle rider applies the brakes in order to come to a stop • A ball at the end of a rope is whirled around a person’s head at a constant speed of 8.0m/s • The world’s fastest women compete in the 100m dash at the Olympics • A marble rolls in a straight path down the hallway Is there ever a time when a motion which is non-uniform overall, is uniform at some point?

  5. Speed, in Plain English • Speed describes how fast something is moving • It is scalar, so we indicate: • Magnitude • Not direction • The standard unit for measuring speed is m/s

  6. Physics Speak! Speed, in • Symbol: • Speed = v • Formula: • Speed = distance time • v = d t • Example: The cyclist reached a maximum speed of 12.0 m/s during the race.

  7. Velocity, in Plain English • Velocity describes the speed and direction of motion • This means it describes how fast an object’s position is changing • Velocity is a vector, so we describe: • Magnitude • Direction • The standard unit for measuring velocity is m/s

  8. Physics Speak! Velocity, in • Symbols: • Velocity = v • Formula: • Velocity = displacement time • v = d t • Example: • The aircraft was traveling at 535km/h, headed 45° north of west

  9. Practice Problem • An object traveling at a constant speed travels due west for 800m in 40s. • What is the speed of the object? • What is the velocity of the object? • v = d/t v = d/t = 800m/40s = 800m due west/40s = 20 m/s = 20 m/s due west • Note: When the object goes in a straight line, the magnitude for speed and velocity will always be the same!

  10. More Practice Problems • An object traveling at a constant speed travels 450 m in 15 s. What is the speed of the object? • 30 m/s • A shell from a rifle has an average speed of 960 m/s. How many meters does it travel in 5 s? How many km in 5 s? • 4800 m • 4.8 km

  11. More Practice Problems • A driver travels 25m/s on a level highway between two towns. It takes the driver 2h to travel between the two towns. How far apart are the towns (in kms)? • 180 km

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