PHY211: Uniform Motion Lab
Objective: To understand the relationship between velocity, distance and time for uniform motion.
Introduction:
Uniform motion is defined as motion with constant velocity. There are various ways to produce uniform
motion, but for this lab we’ll be using an air track. Ordinarily, an object moving on a horizontal surface is
slowed by friction so that its motion is not uniform. An air track allows the moving object to rest on a cushion
of air while moving horizontally, creating a nearly frictionless situation. As a result, the air cart will move at a
constant velocity from one end of the track to the other. This will allow us to take measurements of v, t and d
(velocity, time and distance) so that we can determine the relationship between these quantities.
Procedure:
Note: The air carts should never be on the track when the air is off. Moving the carts along the track with the
air off scratches the track and reduces its effectiveness in creating a frictionless surface.
1. Before beginning this lab, you need to make sure that nothing will cause a change in velocity of your air
cart. Begin by using a level to level the air tracks while the air is off.
2. Turn the air on and place a cart near the center of the track. Adjust the leveling of the track so that the
air cart does not move, but sits stationary in this position. This is necessary because differences in air
pressure along the track will exert a small force on the cart, changing its velocity.
3. Now use the rubber band mounted on the air track as a “launcher” to give your sled a velocity. Pull car
back so that it just touches the end of the track and release it. Pulling it back the same distance each
time you launch will allow you to have the same velocity with each launch.
4. There are two photogates with each air track. These gates need to be adjusted so that the flag on the top
of your cart passes through the photogate signal. The photogates will record two times each, the time
that the cart enters the gate and the time at which it leaves. When you’ve figured out how to launch the
cart, set up your photogates and record the distance between them. Now you are ready to collect data.
Data Collection and Recording:
1. Questions: Before you begin collecting data, answer the questions below on a separate piece of paper.
a. How can you use the data from the photogates to verify that your cart is actually moving at a
constant velocity?
b. If the cart’s velocity is not perfectly constant, how can you quantify the amount by which it is
changing? In other words, what sort of error calculation can you do here?
c. Can you calculate the actual velocity of the cart as it goes through each photogate? What data do
you need to accomplish this?
2. In order to do a statistical analysis of your data, you need to change the distance between the gates to at
least four different distances and you should do at least ten runs at each distance. Create a data table or a
set of tables that will include all of the data you need to determine the relationship between d, v and t
and also to calculate the percent error due to changing velocity. You should create your table on
separate paper. Graph paper works well for this.
3.
When you’ve created appropriate tables, go ahead and collect your data. Make sure everything is
included in the tables you will be turning in.
Data Analysis:
For this part of the lab, you need to figure out how to use your data to write an equation relating t, v and d for
uniform motion. You will want to graph your d and t data in some way that makes sense for this purpose. Be
sure to turn in your graphs as part of your lab write up. Once you’ve determined the relationship between v, t
and d, go back and verify that it makes sense with the velocity data you took using each gate separately. Show
any calculations and be sure to include labels and units on your graphs.
Analysis and Conclusions:
You will turn this lab in as a formal lab write-up which should include sections on objective, procedure, data,
data analysis and conclusion. As part of your conclusion section, answer the following questions:
1. What are possible and reasonable sources of error in this lab?
2. If more than ten runs were made, would the true average value be better ascertained? Give the rationale
for your answer.
3. Can each run be viewed as an independent event? I so, what are the implications?
4. How would the addition of more discrete distance points aid in the determination of your average
velocity?
Of course, you conclusion should also include the equation you came up with, an explanation of what it means
conceptually and your thoughts on how you might improve on the lab if you did it again or what additional
questions you might want to answer. Staple these instructions to your lab when you turn it in.