Question

section vocabulary
displacement the change in position of an object
frame of reference a system for specifying the precise location of objects in space and time
motion an object’s change in position relative to a reference point
speed the distance traveled divided by the time interval during which the motion occurred
velocity the speed of an object in a particular direction

1. describe how is a frame of reference used to describe motion?

1. interpret label the fastest moving object and the slowest moving object in the plot below. explain your reasoning for selecting each line.

distance vs. time

1. apply concepts a runner runs a 1,500 m race on a circular track. the runner stops 100 m from the starting point. what are the distance and displacement traveled by the runner?

1. calculate scientists tracking a flock of ducks found that, on average, the ducks flew 740 km south in 12 h. what were the speed and velocity of the flock of ducks in meters per second? show your work.

Explanation:

Question 1

A frame of reference is a system for specifying the precise location of objects in space and time. Motion is the change in position relative to a reference point. So, a frame of reference provides a reference point (and coordinate system) to measure an object's position change (motion) by comparing its position at different times relative to this reference.

In a distance - time graph, the slope of the line represents speed (slope = $\frac{\text{change in distance}}{\text{change in time}}$). The steeper the slope, the higher the speed. So, the line with the steepest slope is the fastest - moving object, and the line with the least steep slope is the slowest - moving object. We identify the slopes of each line on the “Distance vs. Time” plot: the line with the greatest slope (steepest) has the highest speed (fastest), and the line with the smallest slope (least steep) has the lowest speed (slowest).

• Distance: Distance is the total length of the path traveled. The runner runs a 1500 - m race, so the distance traveled is 1500 m.
• Displacement: Displacement is the change in position of an object (straight - line distance from the starting point to the ending point, with direction). The runner stops 100 m from the starting point, so the displacement is 100 m (in the direction from the start to the stop point on the circular track).

Answer:

A frame of reference provides a reference point (and coordinate system) to measure an object’s position change (motion) by comparing its position at different times relative to this reference.

Question 2