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Unit 6: Simple Machines

The six basic tools hiding inside a wheelbarrow, a doorknob, and a jar lid, and how each one trades force for distance.

7 topics · 25 questions

Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.

Levers

  1. How it worksHow does sliding a lever's fulcrum change how much force you need to lift the same load?
  2. Worked exampleFind how much force is needed to lift a 100 newton rock if the effort arm is 4 times longer than the load arm.
  3. Common mistakeWhy doesn't a lever create extra energy out of nowhere, even though it makes lifting feel so much easier?
  4. Going furtherWhat happens to the force needed as you move the fulcrum closer to the load?
Your turn1 of 2
Find how much force is needed to lift a 354 newton rock if the effort arm is 7 times longer than the load arm.

Pulleys

  1. How it worksHow does a fixed pulley change only the direction of your pull, while a movable pulley changes the force needed too?
  2. Worked exampleFind the force needed to lift a 60 newton bucket using a movable pulley system that cuts the needed force in half.
  3. Common mistakeWhy doesn't a pulley make the total work needed any smaller, even though it can make the force feel smaller?
Your turn1 of 2
Find the force needed to lift a 142 newton bucket using a movable pulley system that cuts the needed force in half.

Wheel and Axle

  1. How it worksHow does turning a wide wheel move a narrow connected axle with far less effort?
  2. Worked exampleFind the mechanical advantage of a wheel and axle if the wheel's radius is 20 centimeters and the axle's radius is 4 centimeters.
  3. Common mistakeWhy doesn't a bigger wheel always mean less force is needed, no matter the size of the axle?
Your turn1 of 2
Find the mechanical advantage of a wheel and axle if the wheel's radius is 45 centimeters and the axle's radius is 6 centimeters.

Inclined Planes

  1. How it worksHow does a longer, gentler ramp reduce the force needed to raise something to the same height?
  2. Worked exampleFind how the needed force changes on a 6 meter ramp compared to a 2 meter ramp lifting the same box to the same 1 meter height.
  3. Common mistakeWhy doesn't a ramp reduce the total work needed to lift an object, even though it lowers the force?
  4. Going furtherWhat happens to the effort needed as a ramp gets steeper and shorter?
Your turn1 of 2
A box needs 215 newtons of force to lift straight up. Find the force needed on a ramp 7 times longer than the height it's lifting the box to.

Wedges

  1. How it worksHow does a wedge's thin edge turn a downward force into a strong sideways splitting force?
  2. Worked exampleFind which wedge splits wood with less force, one with a narrow 10 degree angle or one with a wide 45 degree angle.
  3. Common mistakeWhy isn't a wedge just a moving version of an inclined plane doing the exact same job?
  4. Going furtherWhat happens to how easily a wedge splits wood as its angle gets thinner and sharper?
Your turn1 of 2
One wedge has a narrow 12 degree angle, and another has a wider 49 degree angle. Which wedge splits wood with LESS force?

Screws

  1. How it worksHow is a screw actually an inclined plane wrapped around a cylinder in a spiral?
  2. Worked exampleFind how many full turns a screw needs to sink 2 centimeters into wood if each turn drives it in 0.5 centimeters.
  3. Common mistakeWhy doesn't a screw's twisting motion mean it isn't secretly using ramp physics?
Your turn1 of 2
Find how many full turns a screw needs to sink 7 centimeters into wood if each turn drives it in 0.654 centimeters.

Mechanical Advantage

  1. How it worksHow does every simple machine trade a smaller force over a longer distance for a bigger force over a shorter one?
  2. Worked exampleFind the mechanical advantage of a machine that lets you lift a 200 newton load using only 50 newtons of effort.
  3. Common mistakeWhy can't any simple machine let you do less total work than lifting the object straight up?
  4. Ties togetherHow does a bicycle combine a wheel and axle with gears to multiply a rider's pedaling force?
Your turn1 of 2
Find the mechanical advantage of a machine that lets you lift a 363 newton load using only 35 newtons of effort.