Constant Velocity vs Constant Acceleration
Purpose: To compare displacement vs time and instantaneous velocity vs time graphs for two objects, one moving at a constant speed and one at accelerating.
Procedure:
1. Open the simulation above.
2. Change the settings to the following:
0.0
0.0
10.0
0.0
0.1
3. Start the simulation.
4. Describe the motions of the blue and red car.
5. Reset the simulation. This time pause and resume the simulation every 5 seconds (you will need a stopwatch for this). Record the displacement and instantaneous velocity for each time. The instantaneous velocity is givenin the top digital display on the simulation - the blue car on the left and the red car on the right.
Time (s) Blue Car Red Car
displacement (m) inst. vel. (m/s) displacement (m) inst.vel. (m/s)
0.0 _______________ _______________ _______________ _______________
5.0 _______________ _______________ _______________ _______________
10.0 _______________ _______________ _______________ _______________
15.0 _______________ _______________ _______________ _______________
20.0 _______________ _______________ _______________ _______________
25.0 _______________ _______________ _______________ _______________
30.0 _______________ _______________ _______________ _______________
35.0 _______________ _______________ _______________ _______________
40.0 _______________ _______________ _______________ _______________
45.0 _______________ _______________ _______________ _______________
6. On the same graph, graph displacement vs time for the blue car and for the red car. You may do this by hand (use a best fit curve) or use the Graphical Analysis programs.
7. On the same graph, graph instantaneous velocity for the blue car and for the red car.
8. Which car is moving at a constant velocity and which is accelerating? How do you know? Is the acceleration constant? How do you
9. What would a displacement vs time graph look like for
a) constant velocity?
b) constant acceleration?
10. What would an instantaneous velocity vs time graph look like for
a) constant velocity
b) constant acceleration?
EXTENSION: Free Fall
Aristotle thought that free-falling objects attained their speed instantaneously and that objects fell with speeds proportional to their weight. Galileo did not agree with this (remember the famous cannonball drop from the Leaning Tower of Pisa story?) He thought that objects picked up speed as they fell and that all objects picked up speed at the same rate. Objects fall fairly fast and without rather sophisticated instruments, times and displacements are difficult to measure. Galileo, therefore, rolled objects down ramps with small inclines so that times would be easier to measure. Go to the simulation below. Watch the animation and make a graph of displacement vs.time. How would the motion change as the ramp became steeper? Why did Galileo think he could use this motion to help describe free fall? Does your graph support Aristotle's or Galileo's theory? Why?