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Motion in one dimension

Motion in one dimension. motion is “relative”, or depends on your frame of reference rate is a quantity divided by time. Speed: how fast something is moving. “/” means per, “” means change in Speed = distance / time average speed = total distance covered / time interval.

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Motion in one dimension

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  1. Motion in one dimension motion is “relative”, or depends on your frame of reference rate is a quantity divided by time

  2. Speed: how fast something is moving • “/” means per, • “” means change in • Speed = distance / time • average speed = total distance covered / time interval

  3. If the odometer reads zero at the beginning of a trip and 35 km a half hour later, what is the average speed? Would it be possible to attain this average speed and never exceed 70 km/h on the speedometer? If a cheetah can maintain a constant speed of 25 m/s, it will cover 25 meters every second. At this rate, how far will it travel in 10 seconds? In 1 minute? Questions

  4. Velocity = speed with direction • distinction between speed and velocity is direction • you can have a constant speed and have a changing velocity • average velocity = displacement / time elapsed • ¯v = = x2 - x1 / (t2 - t1) = x / t • instantaneous velocity = average velocity over an infinitesimally short time

  5. Questions: • If an airplane travels 500 km due north in 1 h, what is its velocity? • 250 km due north in 1/2 h? • 125 km north in 1/4 h? • What are three “velocity changers” on a car?

  6. Acceleration = CHANGE in velocity / change in time • it can be felt!! Whenever you’re in an automobile • it can be positive - a car accelerates from 0 - 60 mph in 60 seconds • 60 mph / 60 sec = 1 mi / hr / sec • it can be negative - a car moving at 30 mph comes to a stop in 10 seconds • -30 mph / 10 sec = -3mi / hr / sec

  7. Question: • What is the acceleration of a car that goes from 0 to 100 km/h in 10 s?

  8. Question • What is the acceleration of a mechanical part that moves from 0 - 10 m/s in a time of 1 s?

  9. Free Fall: How Fast • Does an object dropped from your hand accelerate? • What does it mean to say it accelerated 10 m/s2? • ASSUMPTION: Air resistance is negligible! • Freely falling objects are affected only by gravity, “g” • the acceleration of an object falling is about 10 meters per second squared

  10. Question: • If an object is dropped from rest from the top of a cliff, how fast will it be going at the end of 1 second? • What is the speed at the end of 2 seconds? • What is the speed at the end of 10 seconds?

  11. Free Fall: How Fast • acceleration = change in speed / time interval • instantaneous speed = acceleration x elapsed time • v = gt

  12. Question • If you threw a ball straight up with an initial velocity of 30 m/s, how long would it take for it to reach its peak height? • (HINT: Draw a picture!!)

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