7.6 Simple Machines

Last updated at September 16, 2026 by

Example — Pulling a bucket of water from a well
  • Suppose a bucket of water is to be pulled up from a well.
  • There are 2 methods
  • GIF Watch: example — Pulling a bucket of water from a well Animation for "Example — Pulling a bucket of water from a well". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Beat 1 — Suppose a bucket of water is to be pulled up from a well. Beat 2 — There are 2 methods. Beat 3 — Which method is easier?. Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
Method How How it feels
Method 1 — Directly by hand Bend over the well, hold the rope, and pull the bucket straight UP Difficult — we pull upward, against gravity, in an awkward position
Method 2 — Using a pulley Rope goes over a pulley wheel at the top. We pull the rope DOWN, the bucket comes up Easier — we pull downward, our body weight helps us
  • Which method is easier?
    • Method 2 — using the pulley.
    • The amount of water lifted is the same, the height is the same — so the work is the same.
    • But pulling down feels much easier than pulling up.
    • The pulley made the task easier by changing the direction of our force.
What is a Simple Machine?
  • The pulley in the above example is a simple machine.
  • Simple machines are devices that make a task easier by changing the magnitude or direction of the force that needs to be applied.
  • Note — the total work required for a task cannot be reduced . Machines only make the task feel easier.
    In the well example — same work, but a more comfortable direction.:
Which simple machines will we study in this chapter?
We will study 3 simple machines
GIF Watch: which simple machines will we study in this chapter Animation for "Which simple machines will we study in this chapter". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Beat 1 — We will study 3 simple machines. Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
Simple machine What it is Example use
Pulley A wheel with a groove that guides a rope Pulling water from a well, raising a flag
Inclined plane A sloping surface (ramp) Loading a heavy box onto a truck
Lever A rigid bar that rotates about a fixed point Seesaw, scissors, opening a lid with a spoon
What is Effort and Load?
GIF Watch: what is Effort and Load Animation for "What is Effort and Load". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
Term Meaning In the well example
Effort The force we apply to a machine The force with which we pull the rope down
Load The force that needs to be overcome The weight of the bucket of water
What is Mechanical Advantage?
  • To describe how a machine changes the magnitude of the applied force, we define mechanical advantage .
  • It is the ratio of the load to the effort.
  • Mechanical advantage = Load / Effort
  • Mechanical advantage has no unit — it is a ratio of two forces.
What does the value of Mechanical Advantage tell us?
Mechanical advantage Meaning
MA = 1 Effort needed = Load (machine only changes direction)
MA > 1 Effort needed is less than the load (machine multiplies our force)
Example 1 — MA = 1
  • We pull a bucket of weight 50 N from a well using a single pulley.
  • We have to apply a force of 50 N on the rope.
    • Load = 50 N
    • Effort = 50 N
    • Mechanical advantage = Load / Effort = 50 / 50 = 1
  • Effort = Load. The pulley did not reduce our force.
  • It only changed the direction — we pull down instead of up.
Example 2 — MA > 1
  • We lift a heavy box of weight 100 N using a lever.
  • Because of the lever, we only need to apply a force of 25 N.
    • Load = 100 N
    • Effort = 25 N
    • Mechanical advantage = Load / Effort = 100 / 25 = 4
  • Effort is much less than the load.
  • The machine multiplied our force 4 times — a 25 N push handled a 100 N load.
  • The higher the mechanical advantage, the easier the task feels.
Why is there no mechanical advantage in the bucket example?
GIF Watch: why is there no mechanical advantage in the bucket example Animation for "Why is there no mechanical advantage in the bucket example". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Beat 1 — The pulley only changes the direction of our force. Beat 2 — Pulling down is more convenient than pulling up, but the force is not reduced. Beat 3 — So Effort = Load, and MA = 1. Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
  • The pulley only changes the direction of our force.
  • Pulling down is more convenient than pulling up, but the force is not reduced.
  • So Effort = Load, and MA = 1.
📝 Important points — 7.6 Simple Machines
Point Detail
Simple machine Makes a task easier by changing magnitude or direction of force
Total work Cannot be reduced by any machine
Effort Force we apply
Load Force to be overcome
Mechanical advantage Load / Effort (no unit)
MA = 1 Only direction changes
MA > 1 Force is multiplied
💡 Worth remembering
  • Machines make tasks EASIER, not smaller — the work stays the same.
  • MA is just a ratio — no unit.
  • MA = 1 machines are still useful — direction convenience matters.
✅ Quick self-check
  1. We lift a 200 N load using a machine by applying only 50 N effort. Find the mechanical advantage.
    View Answer Hide Answer
    • MA = Load / Effort
    • MA = 200 / 50
    • MA = 4
  2. A machine has MA = 1. Is it useless?
    View Answer Hide Answer
    • No. It does not reduce the force, but it can change its direction .
    • Like a well pulley — pulling down is much more convenient than pulling up.
  3. Can any machine reduce the total work needed for a task?
    View Answer Hide Answer
    • No. The total work cannot be reduced .
    • Machines only change the force's magnitude or direction to make the task feel easier.

Key terms and units

Term Meaning Unit
Effort Force applied to the machine newton (N)
Load Force to be overcome newton (N)
Mechanical advantage Load / Effort No unit
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