Motion Chapter 11

Observing Motion How do you determine if something is moving? Is a person sitting in a driving car moving? If the earth is orbiting the sun, ARE YOU MOVING NOW?

Observing Motion Motion: an object changes position with respect to a reference point Frame of Reference: describes the motion of an object relative to reference points An object is in motion if it changes position with respect to a reference point

Observing Motion Motion can be described in terms of distance, position, displacement, speed, velocity, acceleration, and time Scalar: Quantities that are described by a magnitude (numerical value) only Speed, distance Vector: Quantities that can be described by a magnitude (number) and direction Displacement, velocity, acceleration

Observing Motion Distance: scalar quantity that measures the path taken Displacement: vector quantity that measures object’s overall change in position, how out of place it is, always includes direction

Speed Speed: scalar, refers to how fast an object is moving – how fast it is covering distance Constant Speed: equal distances in equal amounts of time Instantaneous Speed: the speed at any given time Average speed is calculated as total distance divided by total time  v = d/t The SI unit for speed is meters per second (m/s) – smaller units = more precise! You cannot have negative speed

Velocity Velocity: vector, measures rate at which an object changes position AND in which direction (speed + direction!) Velocity can be described as north, south, east, west, as positive/negative depending on the direction of the motion Up, forward, and right are usually positive Down, backwards, and left are usually negative Zero velocity means the object is at rest

Velocity Constant Velocity: same displacement for each time interval Instantaneous Velocity: velocity at any given time Equation and units are the same as speed, however your final answer should include a direction! If you take a step forward and then back, your velocity is 0 because the motion has no change in position

Intervals Interval: space between Time (s) Total distance (m) Average speed (m/s) 1.0 4   2.0 10 3.0 18 4.0 27 5.0 37 6.0 48 7.0 59 8.0 71 9.0 83 10.0 96 10.3 100 Interval: space between Speed and acceleration can be calculated from given intervals How much time has passed between the first and second lines? How much distance was covered between these two times? Between 1 and 2 = 1 second Between 4 and 10 = 6 meters 6/1 = 6 m/s

Graphing Motion Speed is shown with a position (distance) vs. time graph (p-t) In a p-t graph, distance is a function of time – slope represents the speed

What object could have this type of motion?

What object could have this type of motion?

Acceleration Acceleration: vector, measures how much an object’s velocity is changing during a given time (usually 1 second) Change in speed, direction, or both Acceleration can be positive or negative High acceleration: Speeding up or slowing down very quickly, low acceleration: speeding up or slowing down slowly

Acceleration If an object is still, or the object’s velocity is not changing, the object is not accelerating If an object is moving at a constant speed in a circle, the speed is not changing, but direction (velocity) is, the object is accelerating High Acceleration: Speeding up or slowing down, very quickly Low Acceleration: Speeding up or slowing down, slowly

Acceleration Centripetal Acceleration: acceleration that occurs in circular motion Constant Acceleration: when an object’s velocity changes at a constant amount each second

Acceleration To calculate acceleration, subtract the initial velocity (vi) from final velocity (vf) and divide by time a = vf – vi or a = v t t  is called a delta, it means change The SI unit for acceleration is m/s2 (m/s/s)

Graphing Motion Acceleration is shown with a velocity vs. time graph (v-t) In a v-t graph, velocity is a function of time – slope represents the acceleration How to read and interpret graphs

Intervals As before, you can use a motion graph to calculate speed or acceleration during a specific interval What is the acceleration from points D to E?

What object could have this type of motion?

What object could have this type of motion?