Interactive Lecture Demonstration 1 — Investigating Motion with a Sonic Ranger 

In this activity, an ultrasonic motion detector ("Sonic Ranger") will be aimed at various objects. The SR can be used to determine the position, velocity and acceleration of an object, as a function of time. You will be asked to predict graphs of position, velocity and acceleration vs. time for various situations. Your graphs should be sketches; the shape of the graph (and whether the function is positive or negative) is the most important thing here. Make your graphs large so they are legible ! Scales are not needed on the axes, but labels are. All graphs for a given situation must use the SAME TIME SCALE.

Situation 1: A SR is aimed at a wall.

a. Predicted position vs. time graph

b. Predicted velocity vs. time graph

c. How is the velocity graph related to the position graph ?

d. General definition of the slope of a line:

Situation 2: a SR is aimed at a person walking slowly away from the SR; then the experiment is repeated with the person walking away quickly

a. Predicted position vs. time graph (show both walkers on same graph)

b. Predicted velocity vs. time graph

c. Calculated velocity of slow walker (show work completely):

d. Calculated velocity of fast walker (show work completely):

e. Are your calculated velocities in parts c and d average or instantaneous ? Why ?

Situation 3: a SR is aimed at a cart that moves towards a wall, collides with it and bounces back

a. Predicted position vs. time graph (annotate graph with words indicating times when the cart is moving towards and away from the wall, and when the collision occurs)

b. Predicted velocity vs. time graph (annotate as in part a)

Situation 4: a SR is aimed at a cart that rolls down a ramp

a. Predicted position vs. time graph

b. Predicted velocity vs. time graph

c. Predicted acceleration vs. time graph

d. Calculated acceleration of cart while it was rolling down the ramp (show work completely):

Situation 5: a SR is aimed at a cart that rolls up a ramp, then rolls back down

a. Predicted position vs. time graph (annotate with words to show when the cart is rolling up the ramp, when it is rolling down)

b. Predicted velocity vs. time graph (annotate as in part a)

c. Predicted acceleration vs. time graph (annotate as in part a)

d. How should the cart'xs acceleration while rolling up the ramp compare to its acceleration while rolling down ? Why ?