How Do Levers Work? A Firefighter Mechanical Aptitude Question, Worked Step by Step

Every lever question uses the same calculation: find the pivot, measure two distances from it, and balance the turning effect on each side. Multiple-choice lever questions often build their wrong options from distances people measure by habit, such as the full length of the bar.

Below are the three lever classes, the rule that solves all of them, an original question worked step by step, and the mistake behind each wrong option.

What are the three classes of lever?

A lever is classed by which of its three points sits in the middle: the fulcrum (the pivot), the load (whatever you are moving or holding) or the effort (your push or pull). Fulcrum in the middle is first class, load in the middle is second class, and effort in the middle is third class. The class tells you, before any arithmetic, whether the lever can make the job easier.

Class	In the middle	Examples	What it does to force
First	Fulcrum	A pry bar over a block, a claw hammer pulling a nail, a seesaw	Multiplies it, reduces it or leaves it the same size, depending on where the fulcrum sits
Second	Load	A wheelbarrow, a bottle opener, a bar with its tip on the ground lifting something partway along	Always multiplies it
Third	Effort	Your forearm lifting a weight, tweezers, a shovel worked with the back hand held still	Always reduces it, in exchange for speed and reach

One more difference shows up in questions about direction. A first-class lever reverses the motion: push the handle down and the far end rises. In second-class and third-class levers the effort and the load move the same way, so to raise the load you lift.

How do you calculate the force on a lever?

Balance the moments about the fulcrum. A moment is a force multiplied by its distance from the fulcrum, and when a lever is held still, the moment turning it one way equals the moment turning it the other way: effort × effort arm = load × load arm. Rearranged, the effort is the load × load arm ÷ effort arm.

Three habits help you apply the rule correctly:

• Measure both arms from the fulcrum. Not from the end of the bar, and not from the other force. Mistakes at this step cause many wrong answers.
• Use the same units for both arms. Centimetres with centimetres, metres with metres. Only the ratio matters, so matching units cancel out.
• Know what the answer should look like. The effort arm divided by the load arm is the mechanical advantage. If it is 4, the effort is a quarter of the load and your hands travel four times as far as the load does. A lever trades force for distance, and an ideal one never reduces the work.

Strictly, each arm is the perpendicular distance from the fulcrum to the line of the force. Test drawings usually show a level bar with vertical forces, so the arms can be read straight off the bar. If a straight bar is tilted and the forces stay vertical, both arms shrink in the same proportion and the answer does not change.

Can you solve this lever question?

You can if you classify the lever before you calculate. Have a go before you look at the working. The question is ours, written for this post, and its numbers are kept round for easy arithmetic.

A firefighter slides a 2.0 m steel bar under the edge of a heavy steel plate so that the tip of the bar rests on the ground. The edge of the plate presses down on the bar 0.4 m from the tip, with a force of 1,200 N (newtons, the metric unit of force). The firefighter lifts the bar with both hands at a point 1.6 m from the tip. Ignoring the weight of the bar, what upward force must the firefighter apply to hold the plate steady?

• A. 240 N
• B. 300 N
• C. 400 N
• D. 4,800 N

How do you work out the answer?

The answer is B, 300 N. The plate sits between the grounded tip and the hands, so this is a second-class lever with a load arm of 0.4 m and an effort arm of 1.6 m, and 1,200 × 0.4 ÷ 1.6 = 300 N. Here is the reasoning in order.

Step 1: Name the three points. The tip rests on the ground and the bar turns about it, so the tip is the fulcrum. The plate is the load. The hands supply the effort.

Step 2: Classify. Read along the bar from the tip: fulcrum at 0 m, load at 0.4 m, effort at 1.6 m. The load is in the middle, so this is a second-class lever. That settles two things before any arithmetic: the firefighter lifts upward, and the effort must come out below 1,200 N.

Step 3: Measure both arms from the fulcrum.

Arm	From	To	Length
Load arm	The tip (fulcrum)	The edge of the plate	0.4 m
Effort arm	The tip (fulcrum)	The firefighter's hands	1.6 m

The bar's full length, 2.0 m, appears nowhere in this table. Nothing pushes on the last 0.4 m of the bar, so the full length is not needed. It is included to test whether you will use it.

Step 4: Balance the moments. The plate's moment about the tip is 1,200 N × 0.4 m = 480 newton-metres. The hands must match it: effort × 1.6 m = 480 newton-metres, so the effort is 480 ÷ 1.6 = 300 N.

Step 5: Check. The mechanical advantage is 1.6 ÷ 0.4 = 4, and 1,200 ÷ 4 = 300, so the two routes agree. The trade-off is distance: to raise the edge of the plate 5 cm, the hands rise 20 cm. The forces add up too. The hands take 300 N of the plate's push, so the ground under the tip takes the other 900 N.

Why are the other answers wrong?

Each wrong option puts the wrong distance into the balance: an arm that starts or ends at the wrong point, or the two arms swapped. Each of these mistakes is common enough to be worth recognizing.

• A, 240 N, uses the length of the bar as the effort arm: 1,200 × 0.4 ÷ 2.0. An arm runs to where the force is applied, which is the firefighter's hands at 1.6 m, not the end of the steel. The bar's length is the effort arm only when the hands are at the very end.
• C, 400 N, measures the effort arm from the plate to the hands, 1.6 − 0.4 = 1.2 m, and divides 480 by 1.2. That subtraction belongs to a pry bar over a block, where the fulcrum sits between the two forces, so a distance given along the bar has to be split into two arms running outward from it. Here both arms start at the tip, the load arm lies inside the effort arm, and nothing is subtracted. Classifying the lever first prevents this mistake.
• D, 4,800 N, turns the ratio upside down: 1,200 × 1.6 ÷ 0.4. The prediction from step 2 catches it at once, because a second-class lever always needs less effort than the load, and 4,800 N is four times the load. It is in fact the right answer to a different lever, the third-class arrangement below.

How does the same bar behave in each lever class?

The class determines whether the bar reduces the effort, and by how much. Keep the plate's 1,200 N push and the same distances, rearrange the three points, and the effort runs from a fifth of the load to four times the load.

Arrangement	In the middle	Class	Effort arm	Load arm	Effort needed
Tip on the ground, plate at 0.4 m, hands at 1.6 m (the question)	Load	Second	1.6 m	0.4 m	300 N, lifting
The same, with the hands at the far end of the bar	Load	Second	2.0 m	0.4 m	240 N, lifting
Plate on the tip, a block under the bar 0.4 m along, hands at the far end	Fulcrum	First	1.6 m	0.4 m	300 N, pushing down
Tip hooked under a fixed rail, hands at 0.4 m, plate at 1.6 m	Effort	Third	0.4 m	1.6 m	4,800 N, lifting

The table shows three things. Sliding the hands to the end of the bar cuts the effort from 300 N to 240 N, because it lengthens the effort arm, which is why you grip a long handle at its end. The first-class version needs the same 300 N as the question, but pushing down, so body weight can go into it, while the block underneath carries the plate's push and the firefighter's together, 1,500 N. The third-class version shows why that arrangement is a poor way to lift anything heavy: a third-class lever gives speed and reach but needs more force than the load.

Do firefighter aptitude tests ask about levers?

Not by name in any official test description we read. The National Testing Network and Edmonton Fire Rescue Services both describe a mechanical component, but neither lists levers among its topics.

As of October 2026, the National Testing Network's firefighter test page describes the FireTEAM mechanical test as a multiple-choice test shown on video, built around an animated brick-making factory. Most of its questions, NTN says, cover basic mechanical objects and principles, and the examples it gives are valves and water pressure. Candidates also answer troubleshooting questions and watch the system in operation for problems. The same page says the mechanical test in NTN's Firefighter (Express) Exam measures mechanical reasoning and aptitude and shows an image with every question.

Edmonton Fire Rescue Services' recruitment page, read in October 2026, names maps, diagrams and mechanical reasoning as skills its aptitude test measures, and says the aptitude test accounts for 40% of a candidate's overall score. It does not say which mechanical topics come up, and the same page says Edmonton is updating its recruitment process for the 2027 intake, so check it again before you plan around that weighting.

So treat lever practice as general mechanical reasoning practice. It does not predict what a particular test will ask. The moment rule also applies beyond levers. Valves are one of NTN's own examples, and a valve handle works on the same principle as a hydrant wrench: the longer the arm, the less force it takes to turn a stiff spindle or nut.

How should you handle lever questions under time pressure?

Use the same four steps every time, in this order:

1. Name the three points: fulcrum, load, effort.
2. Classify by the middle point, and predict. Second class means the effort is less than the load, third class means it is more, and first class depends on where the fulcrum sits.
3. Measure both arms from the fulcrum, and ignore any length that nothing pushes on.
4. Balance and check: effort × effort arm = load × load arm, then rule out any option that breaks your prediction from step 2.

Step 2 on its own often removes an option or two before you multiply anything. Practise the four steps on Semparo's free mechanical sample questions until you follow the order without thinking about it.

Where can you practise more lever questions?

Levers are one of seven topics in Semparo's mechanical aptitude bank, which runs to 500 original questions across pulleys, gears, hydraulics, tools, valves and pressure as well, and explains the reasoning behind every answer. Ten of them are free samples that a free account opens, and the first lesson in the bank's study guide, on levers and mechanical advantage, is free to read as well.

Once single questions are routine, practise with a time limit. Semparo's four-section FireTEAM-style mock gives the mechanical section 15 questions on its own 15-minute clock, alongside human relations, math and reading. That section timing is ours: NTN's firefighter test page gives only an approximate total test time of two hours. For the whole bank, its study lessons and the timed mocks, you need either the Aptitude section or Pro, so check which plan suits the test you are facing before you pay for anything.