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
Questions 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?
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 = = x 2 - x 1 / (t 2 - t 1 ) = x / t instantaneous velocity = average velocity over an infinitesimally short time
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?
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
Question: What is the acceleration of a car that goes from 0 to 100 km/h in 10 s?
Question What is the acceleration of a mechanical part that moves from 0 - 10 m/s in a time of 1 s?
Free Fall: How Fast Does an object dropped from your hand accelerate? What does it mean to say it accelerated 10 m/s 2 ? 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
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?
Free Fall: How Fast acceleration = change in speed / time interval instantaneous speed = acceleration x elapsed time v = gt
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!!)