# Hands-On-PhysicsMECHANICS

## - Core Project Introduction -

#### Background:

Dragging heavy objects over rough ground or choppy water is an age-old drudgery. Humans have invented many ways to make this simple process easier. We have enlisted the help of stronger animals like horses, and later we created fuel burning engines to replace work animals. We invented the wheel, refined it, and used it in many clever ways. We built boats and powered them with oars, sails, and then with engines. Even more amazing is the fact that we created vehicles which fly! Vehicles which travel on land may be moved forward by pushing backward on the surface of the roadway and boats may be propelled by pushing backward on the water they float in. To fly, one of the technical problems which had to be solved was propulsion; what can you push against? The spinning "air screw" or propeller was developed to push against the obvious - air. Not only did this technical innovation allow engine powered flight, but it provided another possibility for moving terrestrial vehicles as well. One of the important drawbacks of this mode of propulsion has been its general inefficiency.

#### A Story:

In support of bio-diversity you are assembling a research team to search the globe for rare and endangered species. To make this exploration possible, you look for a vehicle which will be helpful in undeveloped wilderness. You soon discover that standard "all-terrain" vehicles are limited because they depend on solid ground to push themselves along. This earth-pushing propulsion technique is not useful for crossing wetlands, or rivers, or snow fields. It doesn't seem like a good technique for crossing from tree-top to tree-top on cables at the top of the rain forest. You recall that the problem of powering aircraft was solved by pushing on air. Perhaps this technology will meet your needs. You build a model to test some of your ideas

#### Questions:

• How does the push of air effect the motion of the aircart?
• Is this a constant push or does it depend on the speed of the aircart?
• What transportation problems could an aircart solve?
• What are its drawbacks?
• How efficient is it?
• What's its maximum speed?
• What about starting and stopping?
• Can it carry a load?

#### Performance Criteria

Before designing an aircart it is important to establish performance criteria
• The aircart must move on its own power (3 volts from two AA batteries)
• Several things should be maximized. Two essential considerations are:
• the aircart's top speed (terminal velocity)
• its ability to speed up (accelerate)
• Also important are: