Simple Machines — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
A seesaw is an example of a pulley.
Corrected: A seesaw is an example of a lever.
A seesaw is a stiff bar that pivots on a fixed point in the middle, which is exactly how a lever works. A pulley uses a rope and a grooved wheel, so it does not match a seesaw.
2. Fix the sentence:
A ramp is a type of wedge that helps move heavy objects up.
Corrected: A ramp is a type of inclined plane that helps move heavy objects up.
A ramp is a flat sloping surface, and that is the definition of an inclined plane. A wedge has a thin edge that splits things apart, which is a different job.
3. Fix the sentence:
A doorknob is an example of a screw.
Corrected: A doorknob is an example of a wheel and axle.
A doorknob turns a small rod (the axle) when you grip the larger round knob (the wheel), so the two pieces work together as a wheel and axle. A screw uses spiral grooves to hold things, which a doorknob does not do.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A simple machine makes work easier by changing the amount of force needed.
Simple machines do not change the total work, but they let you push or pull with less force to get the same job done. So the missing word is force.
2. There are six types of simple machines.
There are six classic simple machines: lever, pulley, wheel and axle, inclined plane, wedge, and screw. Counting them gives the number six.
3. A lever is a bar that turns on a fixed point called a fulcrum.
Every lever needs a fixed turning point so the bar can swing up and down, and that turning point is called the fulcrum. Without a fulcrum the bar could not lift a load.
4. A pulley is a simple machine that uses a rope and a wheel to lift heavy loads.
A pulley has a rope that runs over a grooved wheel so you can pull down to lift a load up. That description matches the missing word pulley exactly.
Part C: True or False?
Read each statement. Circle True or False.
1. A lever helps lift heavy objects by using a fulcrum.
True False
True. The fulcrum gives the lever a turning point, so a small push on one end can lift a heavy object on the other end.
2. An inclined plane makes it harder to move objects to a higher place.
True False
False. An inclined plane makes lifting easier, not harder, because you trade a short steep climb for a longer, gentler push up the slope.
3. A screw is a type of inclined plane wrapped around a rod.
True False
True. If you imagine unrolling the spiral threads of a screw, you get a long ramp, which is why a screw is really an inclined plane wrapped around a rod.