Levers and moment of force – equilibrium about a pivot
Integrated ScienceForces & MotionAges 13–14
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Forces & Motion
The lever's pivot can sit at the centre (a seesaw or balance) or at one end (a wheelbarrow). Drag the two forces along the bar to change the lever arms d₁ and d₂; the bar tilts toward the side with the larger moment, balancing when F₁·d₁ = F₂·d₂. The moment on each side, the force needed for balance, and the mechanical-advantage conclusion update continuously.
Lesson: Moment of a force; Levers and their applications
What it shows
The turning effect of a force about a pivot is its moment, M = F × d, where d is the perpendicular distance from the pivot to the line of action of the force. A lever is balanced when the clockwise and counterclockwise moments are equal, F₁·d₁ = F₂·d₂, the principle of moments. The bar can have its pivot in the middle, like a seesaw, or at one end, like a wheelbarrow, where load and effort act on the same side. When d₂ is longer than d₁, a small effort balances a large load, but the effort moves through a greater distance.
How to use
Start from the default values, 10 N at 20 cm against 5 N at 40 cm, and press Release bar to show that the bar stays level. Drag either force along the bar to change a lever arm and watch the bar tilt toward the larger moment. Press Hold level, change the forces, then press Set F₂ for balance to check your calculated effort. Repeat with the other Lever type.
Parameters you can change
- Force F₁ (load) 1–50 N
- Lever arm d₁ 5–60 cm
- Force F₂ (applied force) 1–50 N
- Lever arm d₂ 5–60 cm
- Lever type Pivot at the centre (seesaw, balance, pliers), Pivot at one end (wheelbarrow, bottle opener)
Questions to explore
- How many times longer than d₁ must d₂ be for a 10 N effort to balance a 50 N load?
- Why is a door handle placed as far as possible from the hinges?
- Where is the pivot of a wheelbarrow, and why does this make lifting the load easier?
