Motion Lab · Mini Lab

Describing Acceleration
Using an Accelerometer

When does an object accelerate?

The Accelerometer

Solid line = the string · Dashed line = what the half-circle measures

Reading

Free walk

Standing still
The string hangs straight down.
Front / back
0°
Sideways
0°
Walking speed
0.0

Overhead View

Looking down at yourself

Walk It Yourself

Free mode

Movement of String

Run a trial, then draw the string on that diagram — click inside the half-circle, or press Stamp to copy what the sim showed.

How to use this simulation

  1. Look at the card first. The string hangs from the tape at the top, the half-circle is the scale you read it against, and the arrow at the bottom shows which way you are walking.
  2. Press a trial button — Speeding Up, Slowing Down, Steady Pace, or Left Turn. Each one walks for you and matches a step in the lab procedure.
  3. Watch which side of the card the string swings to. The + side means positive acceleration, the − side means negative acceleration, and straight down means no acceleration at all.
  4. Check the Reading box while the trial runs. Front / back is the angle the half-circle measures; Sideways is the string swinging out of the card, which only happens when you turn.
  5. Use the Overhead View for the turn. It shows your path from above and the direction the string swings compared to the way you are walking.
  6. Record what you saw in Movement of String. Click inside a diagram to draw the string yourself, or press Stamp to copy the biggest swing from that trial.
  7. Try Walk it yourself. Push the top slider forward to speed up, pull it back to slow down, and use the bottom slider to turn. Reset everything starts over.

Why the string moves

The washer at the end of the string keeps doing what it was already doing. When you speed up, the card moves ahead and the washer lags behind — so the string swings backward, to the + side. When you slow down, the washer keeps going and swings forward, to the − side. The string always leans opposite the acceleration.

The size of the lean depends on how hard you accelerate:

tan(angle) = acceleration ÷ 9.8 m/s²
+Speeding up — string swings back toward the + mark.
−Slowing down — string swings ahead toward the − mark.
0Steady pace in a straight line — string hangs straight down. No acceleration.
⊥Turning — the string swings out of the card, toward the outside of the turn. Changing direction is acceleration too, even when your speed never changes.