A primary school teacher needs a teaching aid that demonstrates the three classes of lever to young children. Fig 1 shows a simple first-class lever. Design...

(a) Four additional functional points [4 marks]

The brief specifies a teaching aid for three classes of lever, interchangeable parts, clear labelling for children aged 7-11. Each additional point earns 1 mark:

1. Desk stability - the device must be stable on a classroom desk or table so it does not tip during demonstrations, even when weights are applied to one side of a beam. A wide, heavy base achieves this. [1]
2. Adjustable fulcrum - the fulcrum position must be movable so the teacher can reconfigure the beam to show all three lever classes (fulcrum between load and effort, load between fulcrum and effort, effort between fulcrum and load). [1]
3. Colour-coded labels - the effort and load positions should be clearly colour-coded (e.g., red for effort, blue for load, green for fulcrum) so young children can distinguish them. Text labels should use large, clear lettering. [1]
4. Safety - no sharp edges, no pinch points, and no small detachable parts that could injure primary-age children. All corners should be rounded and all weights should be too large to swallow. [1]

(b) Two types of lever arrangement [4 marks]

Each arrangement earns 2 marks for a clear sketch with annotation explaining the mechanical principle.

1. First-class lever - the fulcrum is positioned between the effort and the load (e.g., a seesaw). The effort is applied downward at one end and the load is lifted at the other. When the effort arm is longer than the load arm, the mechanical advantage is greater than 1, meaning less effort is needed to lift the load. This is the most common lever class to demonstrate. [2]
2. Second-class lever - the load is positioned between the fulcrum and the effort (e.g., a wheelbarrow). The fulcrum is at one end, the effort at the far end, and the load sits in between. This arrangement always gives a mechanical advantage greater than 1 because the effort arm is always longer than the load arm. [2]

Third-class lever (effort between fulcrum and load, e.g., tweezers) is also a valid example, giving a mechanical advantage less than 1 but increasing speed and range of movement.

(c) Three design ideas [12 marks]

1. Idea 1: Baseboard with sliding fulcrum - a single 400 mm acrylic beam rests on a triangular fulcrum block that slides along a central rail on a baseboard. Colour-coded hooks at regular intervals allow hanging weights at different positions. The teacher reconfigures the fulcrum position for each class. Simple but may confuse younger children since the same beam represents all three classes. [4]
2. Idea 2: Vertical demonstration board with three fixed levers - a 500 mm x 400 mm plywood board with three separate lever beams mounted horizontally at different heights, each permanently set up as one class. Spring balances at the effort points show force, and standard masses hang from load points. A carrying handle and fold-out stand at the back allow portability between classrooms. [4]
3. Idea 3: Modular construction kit - interlocking plastic beams, pivot connectors, and weight hangers stored in a compartmented tray. Children build each lever class themselves following instruction cards. Highly interactive but small parts could be lost or broken, and assembly time reduces teaching time. [4]

(d) Evaluation and justification [8 marks]

Idea 2 (vertical demonstration board) is the strongest choice. It shows all three lever classes simultaneously on one board, allowing the teacher to compare them side by side without stopping to reconfigure. The permanent setup eliminates preparation time and the risk of lost parts. The spring balances add a quantitative element (children can read the effort force and compare it to the load). The carrying handle and fold-out stand make it portable. [2 marks for justified selection]

Idea 1 may confuse younger children because the same beam is reused for all three classes, making the distinctions less clear. Idea 3's small parts are a management challenge in a primary classroom and assembly time cuts into the lesson. The board's larger size is its only disadvantage, but the educational benefit of side-by-side comparison outweighs this. [up to 6 marks]

(e) Detailed final drawing [12 marks]

• Board: 500 mm wide x 400 mm tall x 12 mm birch plywood
• Three acrylic lever beams: each 350 mm long, 30 mm wide, 5 mm thick cast acrylic (each a different colour for identification)
• Beams spaced 100 mm apart vertically on the board
• Each beam pivots on a 6 mm diameter steel pin pressed into a 30 mm x 30 mm x 25 mm plywood support block, which is glued and screwed to the board
• Class 1 lever: pivot block at beam centre (175 mm from each end), load hook at left, effort hook at right
• Class 2 lever: pivot block at left end, load hook at 120 mm from left, effort hook at right end
• Class 3 lever: pivot block at left end, effort hook at 120 mm from left, load hook at right end
• Each hook: bent 3 mm diameter steel wire epoxied into a 3 mm hole drilled in the beam
• Fold-out MDF stand: 200 mm x 300 mm, hinged at the bottom rear with 50 mm brass butt hinges, held at 60 degrees by a cord limiter
• Carrying handle: 150 mm length of 25 mm diameter hardwood dowel, screwed through two angle brackets at the top centre

(f) Materials and reasons [4 marks]

1. 12 mm birch plywood for the backboard - strong, lightweight, smooth surface suitable for printing or sticking labels, and resists warping. Birch gives a clean, classroom-appropriate appearance. [1+1]
2. 5 mm clear cast acrylic for the lever beams - rigid enough to act as levers under load, available in colours for coding each lever class (red, blue, green), and transparent so children can see through the beam to any scale markings on the board behind. [1+1]

(g) Manufacturing the backboard [6 marks]

1. Mark out a 500 mm x 400 mm rectangle on 12 mm birch plywood using a steel rule and try square. [1]
2. Cut to size using a panel saw or circular saw with a fine-tooth blade, cutting on the waste side of the line. Smooth all edges with 120-grit sandpaper wrapped around a sanding block. [1]
3. Mark and drill three 6 mm diameter pivot-pin holes using a pillar drill with a brad-point bit. Clamp the board to the drill table with a backing board beneath to prevent breakout on the underside. [1]
4. Mark positions for the stand hinges and handle brackets. Drill 3 mm pilot holes for the screws at each marked position. [1]
5. Seal and label - apply a coat of clear acrylic varnish or white primer to seal the surface. When dry, apply printed adhesive labels identifying each lever class ("Class 1", "Class 2", "Class 3") with colour-coded backgrounds. [1]
6. Assemble hardware - attach the stand hinges, handle brackets, and pivot support blocks using PVA glue and countersunk wood screws. Thread the cord limiter between the stand and the board back. [1]