Measuring g in a Free Fall Lab: Method, Data and Error Analysis

You can measure g in a free fall lab by recording how far an object falls and how long it takes, then calculating its acceleration from those measurements. A useful experiment also examines how timing, distance measurements, and air resistance affect the result. Here’s a method, a worked example, and a way to explain your findings.

What do you do in a physics lab experiment?

In a free fall experiment, you release an object from rest and measure its downward displacement and elapsed time. A compact, relatively dense object helps reduce the effect of air resistance, though it does not eliminate it.

1. Choose a vertical drop distance and measure from the object’s release position to the position where timing stops.
2. Set up a timer or sensor that starts at release and stops at the endpoint. Follow the equipment instructions.
3. Release the object without pushing it, and record the distance h in meters and time t in seconds.
4. Repeat the trial and collect measurements at several distances if the equipment allows. Keep the same measurement method throughout.
5. Calculate g for each trial or use a graph to estimate it from the full data set.

For a drop from rest, h = ½gt², so g = 2h/t². This model assumes approximately constant gravitational acceleration and negligible air resistance. If the object has an initial downward velocity, the equation also needs a term for that velocity.

See classic physics experiments explained for context on how experiments test physical ideas.

How do you analyze a physics lab gravity experiment?

The following are illustrative measurements, not results from an actual experiment. Distances are downward displacements from rest, and times are measured from release.

Using the last row alone, g = 2(1.220 m)/(0.50 s)² = 9.76 m/s². This is a sample calculation, not a substitute for analyzing all your measurements.

To use the whole data set, plot h on the vertical axis against t² on the horizontal axis. Under the model h = ½gt², the best-fit line’s slope is g/2, so multiply the slope by two. Check the intercept: an unexpected nonzero value can point to an offset or a mismatch between the model and measurement setup. Do not force the line through zero without explaining why.

How hard is a physics lab?

The calculation is manageable, but measuring a short fall accurately can be challenging. A small timing error matters because time is squared in the formula for g.

Percent error: Compare the measured value with a reference using |measured value − reference value| ÷ reference value × 100%. For 9.76 m/s² and a reference of 9.81 m/s², the percent error is |9.76 − 9.81| ÷ 9.81 × 100% ≈ 0.51%. Local gravitational acceleration varies slightly, so use the reference specified by your instructor when one is provided.

• Timing: Human reaction time can affect both the start and stop of a stopwatch. Repeated trials can reveal variation, but they do not necessarily remove a consistent delay.
• Distance: Measuring from inconsistent points on the object or apparatus can introduce an offset.
• Release: A push gives the object an initial velocity, violating the from-rest assumption.
• Air resistance: Drag generally reduces downward acceleration below the ideal free fall value.

Percent error is not the same as measurement uncertainty. Report the uncertainty indicated by your instruments or analysis, explain how it affects the result, and compare the reference value with the range supported by your measurement.

How do you write a physics lab report?

State the question and method, show the data with units, and explain how you calculated g. Include a labeled graph if you used one, along with its fitted slope and the resulting acceleration.

In the conclusion, give your result and uncertainty, compare it with the chosen reference value, and discuss specific sources of error and their likely effects. Avoid saying that human error caused a discrepancy without explaining what happened and how it could influence the measurement.

For a fuller structure, see how to write a physics lab report.

How does an online physics lab work?

An online lab can use a simulation to let students operate virtual instruments, collect data, and analyze results in a browser. The details depend on the lab: follow its instructions for the measurements, calculations, and report.

The UPI Study Physics Lab course includes a free fall activity using position data, velocities, and a graph and slope. The table summarizes the course details.

For a broader explanation of this format, read how an online physics lab works.

Which colleges list Physics Lab on an equivalency chart?

These colleges show Physics Lab (PHYS 200L) on their equivalency charts with UPI Study. Open a college for its full chart.

See the rest of the equivalency on the Physics Lab course page, or open a college above for its full chart. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.

Frequently Asked Questions about Physics Lab

Final Thoughts on Physics Lab

Start by checking exactly where your timer begins and ends, then record several careful measurements. Use the worked example as a guide, but calculate and explain your own result from your own data.