GED Science Practice — Variables, graphs, data tables & scientific reasoning
Read the passage
A researcher investigated the effect of fulcrum placement on the mechanical advantage of a lever, shown in the diagram below.
The researcher collected the data shown in the table below.
Mass Lifted (kg)
Length of Lever (cm)
Effort Distance (cm)
Effort Force (N)
10
200
160
24.5
10
200
120
65.3
10
200
80
147
10
200
40
392
Blue = Independent variable | Red = Dependent variable
GED question: Which graph places the independent and dependent variables on the correct axes for this investigation?
Tap a graph to select it, then press "Check my answer."
Graph A
X: Effort Distance (cm) | Y: Effort Force (N)
Graph B
X: Effort Force (N) | Y: Effort Distance (cm)
Graph C
X: Effort Distance (cm) | Y: Mass Lifted (kg)
Graph D
X: Mass Lifted (kg) | Y: Effort Force (N)
Work through each tab to understand why only one graph is correct and the others are wrong.
Interactive lever — see how effort distance affects force
As the effort distance (blue arrow) increases, the effort force needed (red arrow) decreases — and vice versa
Fulcrum
The pivot point of a lever. Moving the fulcrum closer to the load (mass) increases mechanical advantage — less force needed to lift.
Effort Distance
How far from the fulcrum the effort (push/pull) is applied. Longer effort distance = less force needed. This is the independent variable (what the researcher changed).
Effort Force
The force (in Newtons) needed to lift the mass. This is the dependent variable (what was measured as a result).
Mechanical Advantage
The ratio of load force to effort force. A longer effort distance gives greater mechanical advantage — you do the same work with less force over a greater distance.
What the data shows
Notice what changes and what stays constant across all four rows:
SAME in every row
Mass lifted = 10 kg every time Length of lever = 200 cm every time These are controlled variables — held constant so they don't affect results.
CHANGES each row
Effort Distance: 160 → 120 → 80 → 40 cm This is what the researcher deliberately changed — the independent variable.
MEASURED each row
Effort Force: 24.5 → 65.3 → 147 → 392 N This is what responded to the change — the dependent variable.
The relationship
As effort distance decreases, effort force increases. This is an inverse relationship — the curve goes down on the correct graph.
The correct graph — Effort Force vs. Effort Distance
Effort Distance (cm) on the x-axis [independent] | Effort Force (N) on the y-axis [dependent] — this is the CORRECT orientation
Independent vs. Dependent variables — the key rule
The golden rule for graph axes
X-axis (horizontal)
Independent Variable
What the researcher CHANGED
→ Effort Distance (cm)
Y-axis (vertical)
Dependent Variable
What was MEASURED
→ Effort Force (N)
How to identify each variable in this experiment
Column
What it is
Type of variable
Goes on…
Mass Lifted (kg)
Same in all rows (10 kg)
Controlled
Neither axis
Length of Lever (cm)
Same in all rows (200 cm)
Controlled
Neither axis
Effort Distance (cm)
Changes: 160 → 120 → 80 → 40
Independent ✓
X-axis
Effort Force (N)
Measured result: 24.5 → 65.3 → 147 → 392
Dependent ✓
Y-axis
Common trap: Students sometimes flip the axes, putting Effort Force on x and Effort Distance on y — this is wrong because the researcher CONTROLLED the effort distance (changed it deliberately) and MEASURED the resulting force. The cause always goes on x; the effect always goes on y.
Select the correct graph
Tap the graph that correctly places the independent variable on the x-axis and the dependent variable on the y-axis.
Graph A
X: Effort Distance (cm) Y: Effort Force (N)
Graph B
X: Effort Force (N) Y: Effort Distance (cm)
Graph C
X: Effort Distance (cm) Y: Mass Lifted (kg)
Graph D
X: Mass Lifted (kg) Y: Effort Force (N)
Breaking down all four graph choices
CORRECT
Graph A — X: Effort Distance (cm) | Y: Effort Force (N) This is the only correct graph. Effort Distance is what the researcher deliberately changed (independent variable → x-axis). Effort Force is what was measured as a result (dependent variable → y-axis). The curve falls from upper-left to lower-right, matching the data: as distance increases, force decreases.
WRONG
Graph B — X: Effort Force (N) | Y: Effort Distance (cm) This flips the axes. Effort Force (the dependent/measured variable) incorrectly goes on the x-axis, and Effort Distance (the independent variable) incorrectly goes on the y-axis. By convention, the independent variable ALWAYS goes on the x-axis.
WRONG
Graph C — X: Effort Distance (cm) | Y: Mass Lifted (kg) The x-axis is correct (effort distance), but the y-axis is wrong. Mass Lifted never changed — it was always 10 kg. Graphing a controlled variable (constant value) on the y-axis produces a flat horizontal line that shows no relationship. The researcher did not investigate the effect on mass lifted.
WRONG
Graph D — X: Mass Lifted (kg) | Y: Effort Force (N) Mass Lifted never changed in this experiment (always 10 kg), so it was never the independent variable and should NOT go on the x-axis. Graphing it there would show a single point repeated four times at x=10 — no meaningful relationship could be displayed.
GED strategy — "which graph is correct?" questions
Step 1: Find the independent variable — which column has different values in each row?
Step 2: Find the dependent variable — which column shows measurements that responded to the change?
Step 3: Find the controlled variables — which columns have the SAME value in every row? (These don't go on either axis)
