Mechanical Advantage and Velocity Ratio

These revision cards explain what mechanical advantage and velocity ratio and how it affects the cranks and crank shafts involved in pedalos.

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Mechanical Advantage.

What is mechanical advantage?

Mechanical Advantage is the ratio of effort to load. The higher the mechanical advantage the easier it is to lift or rotate and weight. If the load and the effort are equal there is no mechanical advantage.

And What is the formula?

The formula for mechanical advantage is load divided by effort.

Can I have an example?

If you were rotating a tommy bar on a work bench and the distance from the centre of the circle and the end of the lever was 160mm, and the radius of the circle was 20mm, the mechanical advantage would be 8:1.

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Velocity Ratio.

What is velocity ratio?

Velocity ratio is the ratio of the distance moved by the effort divided by the distance moved by the load. The velocity ratio is the opposite of the mechanical advantage so if the mechanical advantage was 4 to 1 the velocity ratio would be 1 to 4.

And What is the formula?

The formula for velocity ratio is the distance moved divided by the effort divided by the distance moved by the load.

Can I have an example?

Imagine a bike cycling up hill, the sprocket has 30 teeth and the pedal gear has 60 teeth. If the pedal gear revolves once the sprocket would rotate twice because sixty divided by thirty is two. The velocity ratio is 2:1

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Mechanical Advantage in Pedalos.

In a pedalo the crank shaft is the part inbetween each wheel, it is a straight piece with two indentations for each foot, one going up and one going down. The throw is the distance between the straight piece and the bottom of the pedal. The deeper the throw the greater the mechanical advantage and the easier the pedalo moves.

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Levers allow people to lift or rotate things that would normally be too heavy. They do this by increasing the mechanical advantage and reducing the velocity ratio. The effort it the force used when the person pushes or pulls the lever. The fulcrum is the point at the centre of the lever, that it rotates from. The load is the thing that you are lifting or rotating. A class one lever would be a wheelbarrow. A class two lever would be a garden fork. A class three lever would be tweezers.

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