Middle school · Signed numbers
Add a signed change on a number line
Start at one number, move left or right, and separate your position from the change in position.
Predict what will happen, press Play, then pause and explain what changed. Every control also works without playback.
Watch the relationship
PausedHD animation studio
From experiment to screen.
Present a crisp Canvas scene, save a full-HD image, or capture your model as a silent video.
Understand what you are seeing
The idea behind the motion.
A number line uses equal distances for equal numerical changes. Adding a positive number moves right; adding a negative number moves left. The endpoint combines the initial position with the entire change. During the journey, the marker shows only the fraction of the change already completed.
A relationship to keep
Position at progress p = start + p × change
Read the symbols alongside the explanation. A diagram shows the relationship; the assumptions tell you when it applies.
- STEP 1
Locate the start
The amber marker shows the initial value. Zero is the reference point; negative values are to its left and positive values are to its right.
- STEP 2
Follow the direction
Move the timeline. The moving dot's horizontal position follows the signed change. Its curved trail separates the journey from the number-line ticks.
- STEP 3
Read the endpoint
Finish the motion and add start plus change. For example, starting at −3 and adding +5 ends at +2, after crossing zero.
Your turn to explain
Make a prediction. Test your reasoning.
You start at 4 and add −6. Where do you finish, and which direction do you move?
Use the values specified in the question. Reset restores the initial values for this investigation.
Compare your explanation
You finish at −2 after moving 6 units left: 4 + (−6) = −2.
Work through a full lesson
Connect the animation to a worked example and practice questions.