seegongsik
Grade 2 (age 7-8)

grade 2 How Machines Work

Tools that help us lift or move heavy things with less force are called simple machines. A lever is a bar resting on a fulcrum; put the fulcrum close to the load and a small push on the far end can lift something heavy. Gears turn together because their teeth mesh, passing the force along, and gears with different numbers of teeth turn at different speeds. In the first picture, move the fulcrum to compare the force needed; in the second, count how many turns each gear makes.

Levers: what the fulcrum changes

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💡 The secret of the lever
①A lever is a bar that tips around a fulcrum to lift a load
②In the picture the load weighs 10; with the fulcrum 1 unit from the load and 5 units from where you push, a push of 2 lifts it
③The closer the fulcrum moves to where you push, the more force you need: 10 in the middle (3 and 3) and 50 at 5 and 1
④At every position, load × units on the load side = push × units on the push side, as in 10 × 1 = 2 × 5
⑤Seesaws, bottle openers and scissors all use levers

Gears: turning together

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⚙️ The secret of gears
①Because the teeth mesh, when one gear turns, the other turns too
②Two meshing gears turn in opposite directions
③When the big gear with 12 teeth turns once, the small gear with 8 teeth turns 12 ÷ 8 = 1.5 times; you can count with the red dots in the picture
④The small gear turns faster, but with less turning force
⑤Clocks, bicycles and blenders have gears inside

Simple machines around us

🛞 Wheels: rolling makes it easy
①Pushing a heavy box along the floor is hard because the box rubs against the floor
②With wheels it rolls, so it can be moved with much less force
③Cars, bicycles, suitcases and carts have wheels
🔧 Ramps: an easy way up
①Pushing something up a slope (a ramp) takes less force than lifting it straight up
②In return, it has to travel a longer distance
③A screw is a ramp wrapped around a rod

Summary

🎯 Simple machines in short
①Lever: with the fulcrum near the load, a small force lifts something heavy
②Wheel: rolling moves things with little force
③Gear: passes force along, and the number of teeth sets how fast it turns
④Ramp: pushing things up a slope takes less force
⑤A bicycle has wheels, gears and levers in its brake handles

Examples and Unit Test

Example 1
Lifting a load of 10 with a lever, the fulcrum is 1 unit from the load and 5 units from where you push. How much force is needed?
1
Load × units on the load side = push × units on the push side, so 10 × 1 = push × 5.
2
10 = push × 5, so the push is 10 ÷ 5 = 2.
▸ 2 (one fifth of the load)
Set the fulcrum 1 unit from the load in the picture and you see a push of 2 and 10 × 1 = 2 × 5.
Example 2
What tools around us use the lever principle?
1
Scissors, bottle openers and nail clippers are all tools that use levers.
2
With the fulcrum in the right place, they let us cut, open or press with little force.
▸ Scissors · bottle openers · nail clippers (all use levers)
Simple machines help us work with less force.
Unit Test
What must a lever have?
①A fulcrum
②A wheel
③Teeth
④A spring
⑤Electricity
▸ ① A fulcrum
1
A lever is a bar that tips around a fulcrum to lift a load.
2
Wheels roll, gears pass force along, and ramps help raise things up high.
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