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 screwdriver is an example of a wedge.
Corrected: A screwdriver is an example of a wheel and axle.
A screwdriver is a wheel and axle, not a wedge, because you turn the handle (the wheel) to spin the shaft (the axle) and drive in screws.
2. Fix the sentence:
A slide on the playground is a type of lever.
Corrected: A slide on the playground is a type of inclined plane.
A slide is an inclined plane, not a lever, because it is a flat, sloped surface that lets you move from a high place to a low place using gravity.
3. Fix the sentence:
A nail is a type of screw because it holds wood together.
Corrected: A nail is a type of wedge because it holds wood together.
A nail is a wedge, not a screw, because its pointed tip pushes wood fibers apart when you hammer it in, just like any thin edge that splits things.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A screw wraps around a rod in a spiral shape to hold things together.
A screw has threads that wrap around a rod in a spiral, and those threads grip tightly to hold pieces together.
2. A longer ramp needs less force to push something to the top.
A longer ramp spreads the work over a greater distance, so you use less force with each push to reach the same height.
3. A bicycle wheel spins around a metal bar called an axle.
The axle is the metal bar that runs through the center of the wheel, and the wheel spins around it so the bicycle can roll forward.
4. A crowbar pries things open because it works as a lever.
A crowbar is a lever because you push down on one end and the bar pivots on a fulcrum to pry the other end upward with greater force.
Part C: True or False?
Read each statement. Circle True or False.
1. A wedge has two slanted sides that meet at a sharp edge.
True False
True. A wedge is shaped like a triangle with two slanted sides that come together at a thin, sharp edge used to split or cut things apart.
2. A longer screw holds tighter than a shorter screw with the same width.
True False
True. A longer screw has more threads gripping the material, so it holds tighter than a shorter screw of the same width.
3. A pulley can only push objects downward, never lift them up.
True False
False. A pulley is designed to change the direction of force, so when you pull the rope down, the load goes up -- that is exactly how pulleys help lift heavy objects.