Lesson Plan
Curriculum Area: Language/Science and Technology
Subject: Oral and Visual Communication
Time: Day 11, double period
Grade, No. of Pupils: 5/24
Lesson Topic: Build a car that will go as fast as possible.
Expectations (Student Behaviours):
1) Apply understanding of friction and acceleration.
2) Modify the wheels to reduce friction.
3) Mount wheels, weights.
4) Learn procedure for lubricating car.
5) Follow instructions.
Teacher Materials:
powdered graphite/oil, sandpaper, electric drill, mitre saw, mitre box, lead (fishing weights, tire balancing weights) solder or steel ball bearings, hammer, nail set, $7.00 in new quarters, a new dime, balance scale, parent volunteers (if possible).
Student Materials:
car kits.
Presentation Steps (Teacher Behaviours)
Throughout this lesson, the teacher is modelling and explaining to the students how to mount wheels, weights and lubricate the cars.
Sequence of Steps for Learning:
Fighting friction :
1) reducing friction is complex, because there are so many points of friction to consider. Primary among these are wheel to axle, and wheel to track (rolling friction).
2) Let’s deal with wheel to axle friction first. The axles supplied with the kits (the four nails) must be used. No substitutes are allowed. There are three areas where they can be improved. (See diagram below).
a) the flare at the tip: when the points of the nail are stamped out, sharp edges are made on the sides that will scratch the inside of the wheel hub if you force it through the wheel immediately. Before inserting the axle into the wheel, file or sand these sharp edges off.
b) The surface of the nail: the surface of the nail should be sanded as smooth as possible. Use 400 grit (or finer) sand paper.
c) The burrs at the head of the nail: put the nail in an electric drill and using a small file, grind off all the extra material from the underside of the nail head. You may also wish to taper the underside a bit to reduce the area of contact with the wheel.
3) wheel to track friction is next. The wheels can be improved, but the only “modification” permitted is to smooth the casting seam on the “tread” of the wheel. This is best done by inserting one of the prepared axles in a wheel, and “chucking” the axle in the electric drill. Force the axle as far into the drill chuck as possible, tighten the chuck, then tap the axle with a nail set and a hammer to ensure the wheel is held as tightly as possible.
4) When the axle and wheel are tight as possible, run the drill at medium speed (a variable speed drill is best) and lightly sand the tread of the wheel to remove all casting marks. This will ensure the wheel will roll with no bumping or bouncing. Be very careful not to let the wheel work loose so the axle can turn inside it, or the resulting friction will quickly melt the hub of the wheel and ruin it. Also be careful not to sand too much off as al wheels must be the same size.
Mounting the Wheels:
1) The blocks of wood in the kit already has axle slots cut in it. These slots are cut to a depth of 1/8” (3.175 mm) and are not always square to the edge of the block. The slots should be deeper, and they MUST be square to the block.
2) Therefore it is a good idea to (at least) check and be sure the slots are at right angles to the block edges.
3) Recut the slots deeper, using a mitre saw and a mitre box, to a depth of ¼” (6.35 mm). This will still allow a 3/8” clearance between the bottom of the car and the track, as required.
4) Carve or rout a cavity in the underside for weight to be placed.
5) When the body is ready for the wheels, insert each axle in a wheel and force the axle into a slot, taking care to ensure that it goes in straight. Force the axle in as far as you can while allowing enough room for the wheel to still turn freely. Make sure there is no binding anywhere. You are not allowed to use washers, bearings or bushings on the axles or wheels.
6) When all wheels are mounted make sure the cat sits evenly on all four wheels. If all four wheels do not contact the ground, the car will not run straight and true.
Lubrication:
Your choice of lubrication can be important. One thing to remember is that petroleum based oils (WD-40, 4-in-1, etc.) attack many plastics, including the plastic in Kub Kar wheels. The plastic can get gummy or sticky, it can become brittle and break easily, or it may just crumble (depending on the oil) in any case, your wheels won’t last.
There are plastic compatible oils available, (LaBelle, available from hobby stores specializing in model railroad supplies). An alternative is powdered graphite, available from Canadian Tire and other hardware stores, and often used in locks.
Apply powdered graphite very carefully. It comes in a small tube and will squirt out in puffs.
1) Apply oil or graphite on axle point where it extends at edge of wheel. Spin wheel lightly.
Weighting the car:
Once the car is free-rolling, and runs ‘true’ it should go like blue blazes, and win every time, right? Wrong. To win anything the car must get some speed up, and to get that we need acceleration. The only way we can get that is to increase the weight, thereby increasing the potential energy it holds sitting at the top of the sloped track in the starting line-up. This also gives it momentum for the “coast” phase of the race as it is going through the finish line gate.
1) The total weight of the car cannot exceed 5 ounces (1441.75 grams). To be truly competitive, your car must be right up to the weight limit. How much is that? Well, it just happens that 28 new quarters ($7.00) and one new dime are very, very close to five ounces. If your car weights that much, you are really close.
2) Keep in mind the weight should be concealed, and must be firmly fixed in place. To weight the car use lead (fishing weights, tire balancing weights, etc), solder, or steel ball bearings. Normally, the weight is imbedded in a cavity cut in the underside of the car body.
For checking at home, a simple balance scale can be made using a long wooden ruler, a couple of paper plates, and the abovementioned coins. (See diagram below).
Evaluation:
Students followed instructions.
If students followed through each step accurately, they will have assembled a competitive car.