Simple Machines — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Scissors are an example of a wheel and axle.
Corrected: Scissors are an example of two levers.
Each blade of a pair of scissors is a stiff bar that pivots on the screw in the middle, so scissors are really two levers joined together. A wheel and axle uses a round wheel turning on a rod, which scissors do not.
2. Fix the sentence:
An axe is a type of pulley used to split wood.
Corrected: An axe is a type of wedge used to split wood.
An axe has a thin sharp edge that pushes wood apart as it is driven down, and that splitting shape is what defines a wedge. A pulley uses a rope and wheel, which an axe does not.
3. Fix the sentence:
A flagpole uses a lever to raise the flag.
Corrected: A flagpole uses a pulley to raise the flag.
A flagpole has a rope that runs up over a small wheel at the top, so pulling the rope down raises the flag up. That rope-and-wheel system is a pulley, not a lever.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A plane is a flat surface that is higher on one end, like a ramp.
An inclined plane is a flat surface tilted higher on one end, like a ramp leaning against a step. The word that completes the name inclined ___ is plane.
2. A wheel and axle work together to make turning easier.
A wheel and axle work as a pair: the wheel is the round outer part and the axle is the rod it spins on. Together they make turning easier.
3. A wedge has a thin edge that is used to push things apart.
A wedge has a thin sharp edge that drives between things and pushes them apart as you press it in. So the missing word is push.
4. Simple machines help people do work using less effort.
Simple machines let you spread a job over more distance so each push or pull feels easier. The word that fits is effort, the muscle work you put in.
Part C: True or False?
Read each statement. Circle True or False.
1. A wheel and axle help reduce friction when moving objects.
True False
True. The wheel rolls on its axle instead of dragging across the ground, so there is much less friction slowing the load down.
2. A wedge is thick on both ends and thin in the middle.
True False
False. A wedge is the opposite shape: thick on one end and thin on the other, so the thin edge can slip in and split things apart.
3. A pulley changes the direction of the force you apply.
True False
True. When you pull down on the rope of a single fixed pulley, the load on the other end goes up, so the pulley flips the direction of your force.