Choose a situation at the bottom: Push / pull, Ramp, Lift or Stack.
Set the values with the sliders, or type a value in the box next to a slider and press Enter. A value outside the allowed range is set to the nearest allowed value.
Change the sliders and watch the scale reading, the free-body diagram and the Graph tab.
Press ● Record to save a reading. The Data & analysis tab plots your readings; switch on the
best-fit line to check your own graph.
In the Lift, press ▲ Up or ▼ Down to ride, or ✂ Fall. Press ⏸ to freeze the ride and record.
Work through the Tasks tab. Write explanations on your worksheet.
The physics
A scale measures the normal force FN it exerts. It shows FN/g as "kg".
Push down / pull up with F: FN = mg + F (push) or FN = mg − F (pull)
On a slope: FN = mg cos θ (friction from the non-slip mat holds the box along the slope)
In a lift (Newton's 2nd law, Blocks 3–4): FN − mg = ma ⇒ FN = m(g + a), a positive upward
Stack: each block pushes on the one below with a force equal to the weight of everything above the contact.
The two contact forces at a surface are a Newton's 3rd-law pair.