Galileo’s Inclined Plane
AP Physics Laboratory
DISCUSSION:
This experiment was devised by Galileo and refuted the Aristotelian thought of motion and at the same
time demonstrated Galileo’s scientific method. Because of his difficulty calculating the time of a freefalling body, Galileo chose to use an inclined plane. The force of gravity on the inclined plane would be
reduced, allowing more accurate calculations of time intervals. Upon his experimentation, he discovered
that the distance traveled by the ball was directly proportional to the square of the time times the
acceleration due to gravity when it was released from rest.
d  vi t 
1 2
at
2
As he tried his approach with inclined planes of different angles, he discovered that the acceleration
changed. He asserted that as the angle of the inclined plane approached 90°, the acceleration approached
our current value of g. Thus, he related acceleration due to gravity with the sin of the angle of the plane.
a = g sin θ
More importantly, he found that all bodies, regardless of weight, fall with the same uniform acceleration.
THE EXPERIMENT:
1. Create an incline plane with the track provided and physics books. Measure the lengths of the sides
and perform trigonometry to determine the angle. Begin with a small angle and be prepared to
increase the angle in future trials. Note the first angle in your lab report.
2. Measure a point on the incline where the marble will be released from on each trial. Note this
distance in your lab report.
3. Steady the track to provide a stable running surface.
4. Practice starting the marble and the stopwatch simultaneously a few times until you are comfortable
calculating the time it takes for the marble to roll down the incline. You may want to use a pencil to
hold the marble in place before releasing it to avoid accidentally giving it an initial velocity.
5. Place the marble on the inclined track at the distance specified on your data sheet. Start the timer
simultaneously with the release of the ball. Stop the timer when the ball reaches the stopping block.
6. Repeat your timing measurements for this distance two more times, recording each in your data table.
Create a column for average time and average time squared in the data table.
7. Repeat the experiment for 4 other track inclines. Record all your data.
ANALYSIS:
In addition to any necessary measurements or calculations from the experiment itself, include the
following in your lab report.
8. Calculate the acceleration for each angle using the first equation in the discussion section. Record all
accelerations in your lab report.
9. Make graphs of acceleration vs. sin θ for the marble on graph paper. The origin (a = 0, sin θ = 0) will
be a data point since the marble will not accelerate when resting on a surface with a zero angle (a flat
surface). Be sure your graph is neatly done and use a good scale.
10. Plot the data in your calculator and write the equation of the line of best fit (y = mx). Draw an
accurate approximation of the line on your graph.
11. From your data, determine the magnitude of the Earth’s gravitational field. Explain how you arrived
at the value of g. (Hint: consider the 2nd equation from the discussion section).
12. Compare your value of g with the correct value (9.81m/s2). What is your percent error? If your
percentage error was greater than 10%, please redo the experiment.
13. What caused your error? How could you have improved the experiment? (Human interference is not
a sufficient cause for error. If you damaged your data significantly, redo the experiment)