What it shows
Levers differ by where the fulcrum, load and effort sit. A seesaw has the fulcrum in the middle, a wheelbarrow has the load in the middle, and tongs have the effort in the middle. Three working ice cream stick levers on one board show each class and how much they help.
The science
A lever is a bar that turns about a fixed point called the fulcrum. In a first-class lever the fulcrum is between the effort and the load, as in a seesaw or a pair of scissors. In a second-class lever the load sits between the fulcrum and the effort, as in a wheelbarrow or a nutcracker, and this always makes the load easier to lift. In a third-class lever the effort is between the fulcrum and the load, as in tongs, a fishing rod or your forearm; it needs more force than the load but moves the load a long way quickly. The closer the effort is to the fulcrum compared with the load, the more force it needs.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A cardboard or plywood base about 40 cm by 30 cm
- Six ice cream sticks or thin wooden strips
- Three paper fasteners or small nails as hinges
- Three bottle caps as load holders and coins as loads
- Rubber bands as force meters
- Glue, tape and labels
Safety
For this project: An adult must hammer any nails and help with the paper fasteners; keep coins away from small children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Glue a small upright post near the middle of the first stick area and pin a stick on top of it so it rocks like a seesaw; this is the first-class lever.
Pin a second stick at one end to a low post on the base so the free end lifts up; glue a bottle cap in the middle for the load; this is the second-class lever.
Pin a third stick the same way but glue the bottle cap at the far end; the effort will be applied in the middle; this is the third-class lever.
Put three coins in each bottle cap as the load.
Hook a rubber band to the effort point of each lever, pull until the load lifts and mark the stretch on a paper strip beside it.
Compare the three strips: the second-class lever needs the least stretch and the third-class the most.
On the first-class lever, move the post closer to the load and show that the effort gets smaller.
Label each lever with its class and a real example, and write the force comparison on the board.
What you should see
Three levers that lift coins when pulled. The rubber band stretches least for the second-class lever and most for the third-class lever, matching the theory, and moving the fulcrum changes the effort on the seesaw.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which class of lever always makes work easier?
The second class, where the load sits between the fulcrum and the effort.
2Why use a third-class lever if it needs more force?
It moves the load further and faster, which is useful for tongs, a cricket bat or your arm.
3Give an example of each class.
Seesaw or scissors; wheelbarrow or bottle opener; tongs or fishing rod.
4How can you reduce the effort on a first-class lever?
Move the fulcrum closer to the load so the effort arm becomes longer.
Take it further
Measure the distances from the fulcrum to the load and the effort on each lever and work out the mechanical advantage as load arm divided by effort arm.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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