Download Expanding Universe Lab

EARTH SCIENCE
NAME:
LAB: EXPANDING UNIVERSE
PER:
DATE:
PURPOSE: To use a two-dimensional analogy to explore the expansion of the Universe.
BACKGROUND AND THEORY
The Hubble Law tells us that our Universe is expanding. We observe galaxies, find their distances
and their velocities, and find that they are all moving away from us. The more distant the galaxy, the
faster it is moving away. From this information, we can estimate the age of our Universe. We
assume that the Universe has always been expanding at the same rate; then we know how long
distant galaxies have been traveling in order to get where they are today! When Hubble made his
plot, he found that the galaxies seemed to lie on a straight line – in other words, their velocities were
proportional to their distances! This discovery led to what is now called Hubble’s Law. This rate of
expansion is called Hubble’s constant (H0). It is written as v = H0 * d.
QUESTION: Do you think the universe is expanding? Why or why not.
PROCEDURE:
1) Blow up the balloon a little bit. DO NOT TIE IT SHUT!
2) Draw and number ten galaxies (dots) on the balloon. Mark one of these galaxies as the
reference galaxy.
3) Measure the distance between the reference galaxy and each of the numbered galaxies. The
easiest way to do this is to use a piece of string. Stretch it the shortest distance between the
two points on the balloon, then measure the string. Record these data in the table. Be sure to
indicate the units you are using.
4) Starting with the partially inflated balloon, time yourself as you blow up the balloon until
full. Record the time on the data page. You can tie the balloon shut this time if you like.
5) Measure the distance between the reference galaxy and each of the numbered galaxies.
Record these data in the table.
6) Subtract the first measurement from the second measurement, record the difference in the
data table.
7) Divide the distance traveled (the difference from step 6) by the time (from step 4) to get a
velocity.
8) Plot the velocity (y-axis) versus the second measurement (x-axis) to get the “Hubble law for
Balloons”. Don’t forget to include titles and units on your graph!
EARTH SCIENCE
NAME:
LAB: EXPANDING UNIVERSE
PER:
DATE:
DATA:
Time to inflate from the partially inflated balloon to the fully inflated balloon: __________ s
Galaxy
First
Second
Number Measurement Measurement Difference
(cm)
(cm)
(cm)
Velocity
(cm/s)
EARTH SCIENCE
NAME:
LAB: EXPANDING UNIVERSE
PER:
DATE:
ANALYSIS QUESTIONS:
1) Draw a best-fit straight line through your data points using a straight edge. The line
should go through (0,0) on your graph. Why?
2) Find the slope of your best-fit line. To find the slope, identify any two points that lie on
the line. These points do not have to be actual data points, but must lie on the line.
Calculate the slope by dividing the difference in the y-coordinates by the difference in the
x-coordinates. Show your work and include the correct units! This slope is called the
Hubble Constant.
3) Take the reciprocal of this slope to find the age of your balloon universe. To find
reciprocal divide 1 by your answer to question 2. Show your work and include units.
If you have done everything correctly, the age of your balloon universe will be measured
in seconds. If you do not get seconds, check your work in questions 2 and 3.
4) How does this age compare to the time it took to blow up the balloon from its partiallyinflated form to its fully-inflated form? Why?
5) What assumptions do you make about your balloon universe when you find its age by
this method? Are these sensible assumptions? (In other words, where is the error?)
6) How would your results change if you used a different reference “galaxy” on the balloon?
If you are not sure, try it!
7) What relationship exists between the speed of the galaxies moving apart and their initial
distance from one another? Describe the relationship and name this Law.