Simple Machines and Work

Grade 7 · Science · Study Guide

An introduction to the six types of simple machines, how they change force or distance, and the physics definition of work.

In science, work has a specific meaning: work is done when a force causes an object to move in the direction of the force. The formula for work is W = F × d, where W is work in joules, F is force in newtons, and d is the distance the object moves in meters. If you push against a wall all day but it doesn't move, you do zero work in the scientific sense.

Simple machines are devices that make work easier by changing the size or direction of a force. There are six types: the lever, wheel and axle, pulley, inclined plane, wedge, and screw. A lever is a rigid bar that pivots around a fixed point called the fulcrum. The mechanical advantage of a machine tells you how much it multiplies your input force — a mechanical advantage of 3 means the machine produces 3 times the force you put in.

A pulley uses a rope and wheels to redirect or multiply force. A single fixed pulley just changes the direction of force; adding more pulleys increases mechanical advantage. An inclined plane (a ramp) lets you move an object to a greater height by spreading the work over a longer distance, requiring less force. A wedge is a moving inclined plane, and a screw is essentially an inclined plane wrapped in a spiral.

Simple machines do not reduce the total amount of work needed — they just make it feel easier by trading force for distance or changing direction. Two or more simple machines combined form a compound machine, like scissors (two levers and two wedges).

Key terms

Work
The product of force and distance when a force causes an object to move in the direction of the force; measured in joules.
Simple machine
A basic mechanical device that changes the magnitude or direction of a force to make work easier.
Mechanical advantage
The ratio of the output force of a machine to the input force; how much a machine multiplies force.
Fulcrum
The fixed pivot point around which a lever rotates.
Inclined plane
A flat surface tilted at an angle used to reduce the force needed to raise an object by increasing the distance over which the force is applied.
Pulley
A simple machine using a wheel and rope that can change the direction of a force or provide mechanical advantage.

Flashcards

Work formula
W = F × d (Work = Force × distance). Work is measured in joules (J), force in newtons (N), and distance in meters (m).
Joule
The unit of work and energy in the SI system; equal to one newton of force applied over one meter.
Lever
A rigid bar that rotates around a fixed fulcrum; can multiply force or change its direction depending on fulcrum placement.
Wheel and axle
A simple machine consisting of a larger wheel attached to a smaller axle; rotating the wheel turns the axle with greater force.
Wedge
A simple machine made of two inclined planes back-to-back; used to split, lift, or hold objects (e.g., an axe blade).
Screw
An inclined plane wrapped in a spiral around a cylinder; converts rotational force into linear force (e.g., a bolt).
Compound machine
Two or more simple machines combined to do work (e.g., scissors = two levers + two wedges).
Mechanical advantage
Output force divided by input force; tells you how much a machine multiplies the force you apply.

Questions

  1. According to the scientific definition, which scenario involves doing work?

    1. Pushing against a locked door that does not move
    2. Holding a heavy box steady without moving it
    3. Lifting a book from the floor to a shelf
    4. Squeezing a rubber ball without it changing position
    Show answer

    Answer: Lifting a book from the floor to a shelf

    Work requires both a force AND motion in the direction of the force. Lifting a book applies an upward force and the book moves upward — that is work. Pushing against an immovable object produces no displacement, so no work is done.

  2. A simple machine can reduce the total amount of work required to complete a task.

    Show answer

    Answer: False

    Simple machines redistribute work — they can reduce the force needed but increase the distance (or vice versa). The total work (force × distance) stays the same, assuming no friction.

  3. The fixed point around which a lever pivots is called the ______.

    Show answer

    Answer: fulcrum

    The fulcrum is the pivot point of a lever. Its position relative to the load and effort determines the mechanical advantage. Moving the fulcrum closer to the load increases mechanical advantage.

  4. A ramp that lets you push a heavy box to a higher level with less force is an example of which simple machine?

    1. Lever
    2. Pulley
    3. Inclined plane
    4. Wheel and axle
    Show answer

    Answer: Inclined plane

    An inclined plane (ramp) lets you use less force over a longer distance to reach the same height. The work done is the same, but the force required is reduced.

  5. A screw is considered a type of inclined plane wrapped in a spiral.

    Show answer

    Answer: True

    A screw is essentially an inclined plane (a ramp) that has been wrapped helically around a cylindrical shaft. Turning the screw converts rotational force into a powerful linear force.

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