Lab: Acceleration Investigation
Purpose: The purpose of this lab is to investigate the relationship between velocity and acceleration of objects that are either speeding up or slowing down.
Procedure:
Part I: upward is positive
1. Set up your lab station as shown in the figure. You should have a frictionless cart on a small incline. A motion sensor is placed on the incline to plot a velocity-time graph of the cart.
2. In this particular situation, up the ramp will be defined as the positive direction and down the ramp will be defined as the negative direction.
3. Place the motion sensor at the bottom of the ramp. Place the cart at the top of the ramp and release from rest so that it slides down the ramp. Determine the signs (+ or -) of all values listed in the table below. Use the velocity-time graph to determine the sign of the acceleration. (Remember that the slope of a v-t graph gives you your acceleration!)
4. Now place the cart at the bottom of the ramp and give it an initial shove up the ramp. Fill in the signs of the values listed in the table below.
Scenario / Speeding up or slowing down? / Sign of displacement (+ or -) / Sign of velocity (+ or -) / Sign of acceleration (+ or -)Rolling down ramp
Sliding up ramp
Part II: Downward is positive
1. Now move the motion sensor to the top of the ramp. This will switch your coordinate system so that positive is defined as down the ramp and negative is defined as up the ramp.
2. Place the cart at the top of the ramp and release from rest so that it slides down the ramp. Determine the signs (+ or -) of all values listed in the table below. Use the velocity-time graph to determine the sign of the acceleration. (Remember that the slope of a v-t graph gives you your acceleration!)
3. Now place the cart at the bottom of the ramp and give it an initial shove up the ramp. Fill in the signs of the values listed in the table below.
Scenario / Speeding up or slowing down? / Sign of displacement (+ or -) / Sign of velocity (+ or -) / Sign of acceleration (+ or -)Rolling down ramp
Sliding up ramp
Analysis Questions:
1. Does a positive acceleration always mean that an object is speeding up?
2. Does a negative acceleration always mean that an object is slowing down?
3. Is there a relationship between the sign of the velocity and the sign of the acceleration that would indicate whether the object is speeding up or slowing down?
4. Suppose a car is traveling in the negative x-direction and comes to a stop. What is the sign of that car’s acceleration? How do you know?