8th Grade Forces, Motion, and Energy 4-2

Explain how using a ramp makes work easier.

A ramp allows you to lift something by pushing it a longer distance using less force.

Analyzing Processes: Describe the effect that friction has on a machine's mechanical efficiency. How do lubricants increase a machine's mechanical efficiency?

Example: Lubricants decrease the fiction in a machine, there by allowing more of the input work to be converted to output work.

How does the meaning of the terms mechanical advantage and mechanical efficiency differ?

Example: Mechanical advantage is the number of times a machine multiplies force. Mechanical efficiency is the ratio of work output to work input of a machine.

Making Inferences: For a machine with a mechanical advantage of 3, how does the distance through which the output force is exerted differ from the distance through which the input force is exerted?

Example: The output force would be applied through a distance one-third that of the distance that the input force is applied.

How does the meaning of the terms work input and work output differ?

Example: Work input is the work done on a machine. Work output is the work done by a machine.

Give a specific example of a machine, and describe how its mechanical efficiency might be calculated.

Example: an elevator; Its work output could be measured by the weight and distance a load is carried upward, and its work input could be measured by the electrical energy it uses to do that work. You would then divide the output work by the input work and multiply by 100 to get a percentage: the mechanical efficiency.

Why can't a machine be 100% effected?

Machines have moving parts in which friction causes energy input to be lost as heat.

machine

a device that helps do work by either overcoming a force or changing the direction of the applied force

mechanical advantage

a number that tells how many times a machine multiplies force

Which of the following is the correct way to calculate mechanical advantage? a) input force divided by output force b) output force divided by input force c) work input divided by work output d) work output divided by work input

b) output force divided by input force

work output

the work done by a machine: the product of the output force and the distance through which the force is exerted.

work input

the work done on a machine; the product of the input force and the distance through which the force is exerted