Year 7 Science · Unit 3 · Lesson 10
Challenge Worksheet
Learning Goals
Odd one out
Each row names a criterion. Using only that criterion, write the odd one out and your reason.
| Criterion | Items | Odd one out, and why |
|---|---|---|
| Class of lever | seesaw, crowbar, nutcracker, scissors | |
| Type of simple machine | axe head, door stop, jar lid, knapped stone flake | |
| Is the MA greater than 1? | movable pulley, fixed pulley on a flagpole, wheelbarrow, block and tackle |
Two traditional tools
Scenario: a digging stick and a stone flake
Aboriginal and Torres Strait Islander Peoples have used and refined these tools over many thousands of years. A digger pushes the tip of a digging stick under a root, then presses down on the long top end, so the stick pivots on the ground at the edge of the hole and the root lifts out. A sharp flake knapped from a stone core slices through tough bark that could not be torn by hand.
1. Which class is the digging stick? Name its pivot, where the digger pushes, and what is lifted. Explain why a small push shifts a root a hand could not.
2. Name the simple machine the stone flake is, and explain how it makes cutting easier without creating any energy.
Read the data: four mystery levers
Scenario: testing levers
Students test four mystery tools, P to S, each used as a lever, without noting where each pivot sits. For each tool they measure both forces, and how far each end moves. Friction is small enough to ignore.
| Lever | Effort (N) | Load (N) | Effort end moves (cm) | Load moves (cm) |
|---|---|---|---|---|
| P | 20 | 80 | 40 | 10 |
| Q | 30 | 10 | 5 | 15 |
| R | 50 | 50 | 20 | 20 |
| S | 25 | 100 | 20 | 8 |
Source: made-up results for this worksheet.
3. Calculate the mechanical advantage (load ÷ effort) of lever P and of lever Q.
P: MA = Q: MA =
4. Which lever could be a Class 3 lever? Which lever can only be a Class 1 lever? Explain both answers using mechanical advantage.
5. One lever’s results must contain a recording error, because they are physically impossible. Identify it, and use the force–distance trade-off to explain why.
6. A student says: “Class 3 levers are pointless, because they make you use more force, not less.” Evaluate this claim, using two examples of Class 3 levers.
Odd one out
Row 1: nutcracker, Class 2; the others are Class 1 (1). Row 2: jar lid, a screw; the others are wedges (1). Row 3: fixed pulley, MA = 1; the others have MA greater than 1 (1). [3 marks]
Two traditional tools
1. Class 1 lever (1). Fulcrum: ground at the edge of the hole; effort: hands on the long top end; load: the root at the tip (1). The effort is much further from the fulcrum than the load, so the MA is greater than 1: a small effort moved through a long arc lifts the root a short distance (1). [3 marks]
2. A wedge (1). It concentrates the user’s force onto the tiny area of its thin edge; it adds no energy (1). [2 marks]
Read the data: four mystery levers
3. P: 80 ÷ 20 = 4 (1). Q: 10 ÷ 30 = 0.33 (1). [2 marks]
4. Q could be Class 3: its MA is below 1, as every Class 3 lever’s is (1). R can only be Class 1: its MA is exactly 1 (1). Class 2 always has MA above 1 and Class 3 below 1; only Class 1 can have MA = 1 (1). [3 marks]
5. Lever S (1). Its effort is a quarter of the load, so its effort end must move at least 4 times as far as the load (32 cm), as in lever P (1). Only 20 cm for 8 cm means more out than in: it would create energy, which no machine can do (1). [3 marks]
Question 6
Marking guide: 1 position (observation right, conclusion wrong); 1 true part: the effort is between the fulcrum and the load, so MA is less than 1 and the effort is bigger than the load; 1 gain: the load end moves further and faster than the effort, giving speed and range of movement; 1 first example with its gain (a fishing rod: a small wrist movement flicks the line a long way); 1 second example with its gain (tweezers: fine control of tiny objects; or the forearm: fast, precise hand movement); 1 judgement: a machine is judged by the job it does, not only by its MA. [6 marks]
Model answer: The student is right that Class 3 levers need more force, but wrong that they are pointless. With the effort between the fulcrum and the load, the MA is below 1, but the load end moves further and faster than your hand. A fishing rod turns a small wrist flick into a long, fast cast. Tweezers let your fingers steer the tips precisely, which is ideal for picking out a splinter. Class 3 levers trade force for speed, range or control, which is often what the job needs.
Common error: treating MA less than 1 as “wasting energy”; it trades force for speed and distance.